// IWYU pragma: begin_exports
// #include "config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "config/macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif

// #include "config/version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif

// #include "container/dense_map.hpp"
#ifndef ENTT_CONTAINER_DENSE_MAP_HPP
#define ENTT_CONTAINER_DENSE_MAP_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CONTAINER_FWD_HPP
#define ENTT_CONTAINER_FWD_HPP

#include <functional>
#include <memory>

namespace entt {

template<
    typename Key,
    typename Type,
    typename = std::hash<Key>,
    typename = std::equal_to<Key>,
    typename = std::allocator<std::pair<const Key, Type>>>
class dense_map;

template<
    typename Type,
    typename = std::hash<Type>,
    typename = std::equal_to<Type>,
    typename = std::allocator<Type>>
class dense_set;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Key, typename Type>
struct dense_map_node final {
    using value_type = std::pair<Key, Type>;

    template<typename... Args>
    dense_map_node(const std::size_t pos, Args &&...args)
        : next{pos},
          element{std::forward<Args>(args)...} {}

    template<typename Allocator, typename... Args>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const std::size_t pos, Args &&...args)
        : next{pos},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::forward<Args>(args)...)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const dense_map_node &other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, other.element)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, dense_map_node &&other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::move(other.element))} {}

    std::size_t next;
    value_type element;
};

template<typename It>
class dense_map_iterator final {
    template<typename>
    friend class dense_map_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_iterator() noexcept
        : it{} {}

    constexpr dense_map_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_iterator(const dense_map_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_map_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_map_iterator operator++(int) noexcept {
        dense_map_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_map_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_map_iterator operator--(int) noexcept {
        dense_map_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_map_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_map_iterator operator+(const difference_type value) const noexcept {
        dense_map_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_map_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_map_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].element.first, it[value].element.second};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->element.first, it->element.second};
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_map_local_iterator final {
    template<typename>
    friend class dense_map_local_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_map_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_local_iterator(const dense_map_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_map_local_iterator &operator++() noexcept {
        return offset = it[offset].next, *this;
    }

    constexpr dense_map_local_iterator operator++(int) noexcept {
        dense_map_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it[offset].element.first, it[offset].element.second};
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for key-value pairs with unique keys.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on the hash of its key. Keys with the same hash
 * code appear in the same bucket.
 *
 * @tparam Key Key type of the associative container.
 * @tparam Type Mapped type of the associative container.
 * @tparam Hash Type of function to use to hash the keys.
 * @tparam KeyEqual Type of function to use to compare the keys for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Key, typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_map {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = internal::dense_map_node<Key, Type>;
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::pair<const Key, Type>>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t key_to_bucket(const Other &key) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(key)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other, typename... Args>
    [[nodiscard]] auto insert_or_do_nothing(Other &&key, Args &&...args) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::piecewise_construct, std::forward_as_tuple(std::forward<Other>(key)), std::forward_as_tuple(std::forward<Args>(args)...));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    template<typename Other, typename Arg>
    [[nodiscard]] auto insert_or_overwrite(Other &&key, Arg &&value) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            it->second = std::forward<Arg>(value);
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(key), std::forward<Arg>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + key_to_bucket(packed.first().back().element.first);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].next) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Key;
    /*! @brief Mapped type of the container. */
    using mapped_type = Type;
    /*! @brief Key-value type of the container. */
    using value_type = std::pair<const Key, Type>;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the keys. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the keys for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Input iterator type. */
    using iterator = internal::dense_map_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_iterator = internal::dense_map_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Input iterator type. */
    using local_iterator = internal::dense_map_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_local_iterator = internal::dense_map_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_map()
        : dense_map{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const allocator_type &allocator)
        : dense_map{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const allocator_type &allocator)
        : dense_map{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_map{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_map(const dense_map &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_map(const dense_map &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_map(dense_map &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_map(dense_map &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_map &operator=(const dense_map &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_map &operator=(dense_map &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if the key does not exist.
     * @param value A key-value pair eventually convertible to the value type.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value.first, value.second);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value.first), std::move(value.second));
    }

    /**
     * @copydoc insert
     * @tparam Arg Type of the key-value pair to insert into the container.
     */
    template<typename Arg>
    std::enable_if_t<std::is_constructible_v<value_type, Arg &&>, std::pair<iterator, bool>>
    insert(Arg &&value) {
        return insert_or_do_nothing(std::forward<Arg>(value).first, std::forward<Arg>(value).second);
    }

    /**
     * @brief Inserts elements into the container, if their keys do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Inserts an element into the container or assigns to the current
     * element if the key already exists.
     * @tparam Arg Type of the value to insert or assign.
     * @param key A key used both to look up and to insert if not found.
     * @param value A value to insert or assign.
     * @return A pair consisting of an iterator to the element and a bool
     * denoting whether the insertion took place.
     */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(const key_type &key, Arg &&value) {
        return insert_or_overwrite(key, std::forward<Arg>(value));
    }

    /*! @copydoc insert_or_assign */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(key_type &&key, Arg &&value) {
        return insert_or_overwrite(std::move(key), std::forward<Arg>(value));
    }

    /**
     * @brief Constructs an element in-place, if the key does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace([[maybe_unused]] Args &&...args) {
        if constexpr(sizeof...(Args) == 0u) {
            return insert_or_do_nothing(key_type{});
        } else if constexpr(sizeof...(Args) == 1u) {
            return insert_or_do_nothing(std::forward<Args>(args).first..., std::forward<Args>(args).second...);
        } else if constexpr(sizeof...(Args) == 2u) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(packed.first().size(), std::forward<Args>(args)...);
            const auto index = key_to_bucket(node.element.first);

            if(auto it = constrained_find(node.element.first, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.next, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Inserts in-place if the key does not exist, does nothing if the
     * key exists.
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param key A key used both to look up and to insert if not found.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(const key_type &key, Args &&...args) {
        return insert_or_do_nothing(key, std::forward<Args>(args)...);
    }

    /*! @copydoc try_emplace */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(key_type &&key, Args &&...args) {
        return insert_or_do_nothing(std::move(key), std::forward<Args>(args)...);
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(pos->first);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].element.first);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given key.
     * @param key A key value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const key_type &key) {
        for(size_type *curr = sparse.first().data() + key_to_bucket(key); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].next) {
            if(packed.second()(packed.first()[*curr].element.first, key)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].next;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_map &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Accesses a given element with bounds checking.
     * @param key A key of an element to find.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &at(const key_type &key) {
        auto it = find(key);
        ENTT_ASSERT(it != end(), "Invalid key");
        return it->second;
    }

    /*! @copydoc at */
    [[nodiscard]] const mapped_type &at(const key_type &key) const {
        auto it = find(key);
        ENTT_ASSERT(it != cend(), "Invalid key");
        return it->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](const key_type &key) {
        return insert_or_do_nothing(key).first->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](key_type &&key) {
        return insert_or_do_nothing(std::move(key)).first->second;
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const key_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given key.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const key_type &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const key_type &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Finds an element with a key that compares _equivalent_ to a given
     * key.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Returns a range containing all elements with a given key.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const key_type &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const key_type &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given key.
     * @tparam Other Type of an element to search for.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given key.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const key_type &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Checks if the container contains an element with a key that
     * compares _equivalent_ to a given value.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given key.
     * @param key The value of the key to examine.
     * @return The bucket for the given key.
     */
    [[nodiscard]] size_type bucket(const key_type &key) const {
        return key_to_bucket(key);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = key_to_bucket(packed.first()[pos].element.first);
                packed.first()[pos].next = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the keys.
     * @return The function used to hash the keys.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare keys for equality.
     * @return The function used to compare keys for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace std {

template<typename Key, typename Value, typename Allocator>
struct uses_allocator<entt::internal::dense_map_node<Key, Value>, Allocator>
    : std::true_type {};

} // namespace std

/**
 * Internal details not to be documented.
 * @endcond
 */

#endif

// #include "container/dense_set.hpp"
#ifndef ENTT_CONTAINER_DENSE_SET_HPP
#define ENTT_CONTAINER_DENSE_SET_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/compressed_pair.hpp"

// #include "../core/memory.hpp"

// #include "../core/type_traits.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class dense_set_iterator final {
    template<typename>
    friend class dense_set_iterator;

public:
    using value_type = typename It::value_type::second_type;
    using pointer = const value_type *;
    using reference = const value_type &;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::random_access_iterator_tag;

    constexpr dense_set_iterator() noexcept
        : it{} {}

    constexpr dense_set_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_set_iterator(const dense_set_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_set_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_set_iterator operator++(int) noexcept {
        dense_set_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_set_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_set_iterator operator--(int) noexcept {
        dense_set_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_set_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_set_iterator operator+(const difference_type value) const noexcept {
        dense_set_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_set_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_set_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return it[value].second;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::addressof(it->second);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_set_local_iterator final {
    template<typename>
    friend class dense_set_local_iterator;

public:
    using value_type = typename It::value_type::second_type;
    using pointer = const value_type *;
    using reference = const value_type &;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::forward_iterator_tag;

    constexpr dense_set_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_set_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_set_local_iterator(const dense_set_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_set_local_iterator &operator++() noexcept {
        return offset = it[offset].first, *this;
    }

    constexpr dense_set_local_iterator operator++(int) noexcept {
        dense_set_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::addressof(it[offset].second);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_set_local_iterator<ILhs> &lhs, const dense_set_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_set_local_iterator<ILhs> &lhs, const dense_set_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for unique objects of a given type.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on its hash. Elements with the same hash code
 * appear in the same bucket.
 *
 * @tparam Type Value type of the associative container.
 * @tparam Hash Type of function to use to hash the values.
 * @tparam KeyEqual Type of function to use to compare the values for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_set {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = std::pair<std::size_t, Type>;
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t value_to_bucket(const Other &value) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(value)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &value, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(*it, value)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &value, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(*it, value)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other>
    [[nodiscard]] auto insert_or_do_nothing(Other &&value) {
        const auto index = value_to_bucket(value);

        if(auto it = constrained_find(value, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + value_to_bucket(packed.first().back().second);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].first) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Type;
    /*! @brief Value type of the container. */
    using value_type = Type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the elements. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the elements for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Random access iterator type. */
    using iterator = internal::dense_set_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant random access iterator type. */
    using const_iterator = internal::dense_set_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Forward iterator type. */
    using local_iterator = internal::dense_set_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant forward iterator type. */
    using const_local_iterator = internal::dense_set_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_set()
        : dense_set{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_set(const allocator_type &allocator)
        : dense_set{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_set(const size_type cnt, const allocator_type &allocator)
        : dense_set{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_set(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_set{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_set(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_set(const dense_set &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_set(const dense_set &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_set(dense_set &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_set(dense_set &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_set &operator=(const dense_set &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_set &operator=(dense_set &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if it does not exist.
     * @param value An element to insert into the container.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value));
    }

    /**
     * @brief Inserts elements into the container, if they do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Constructs an element in-place, if it does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace(Args &&...args) {
        if constexpr(((sizeof...(Args) == 1u) && ... && std::is_same_v<std::decay_t<Args>, value_type>)) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(std::piecewise_construct, std::make_tuple(packed.first().size()), std::forward_as_tuple(std::forward<Args>(args)...));
            const auto index = value_to_bucket(node.second);

            if(auto it = constrained_find(node.second, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.first, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(*pos);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].second);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given value.
     * @param value Value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const value_type &value) {
        for(size_type *curr = sparse.first().data() + value_to_bucket(value); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].first) {
            if(packed.second()(packed.first()[*curr].second, value)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].first;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_set &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Returns the number of elements matching a value (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const value_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given value.
     * @param value Value of an element to search for.
     * @return An iterator to an element with the given value. If no such
     * element is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const value_type &value) {
        return constrained_find(value, value_to_bucket(value));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const value_type &value) const {
        return constrained_find(value, value_to_bucket(value));
    }

    /**
     * @brief Finds an element that compares _equivalent_ to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return An iterator to an element with the given value. If no such
     * element is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &value) {
        return constrained_find(value, value_to_bucket(value));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &value) const {
        return constrained_find(value, value_to_bucket(value));
    }

    /**
     * @brief Returns a range containing all elements with a given value.
     * @param value Value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const value_type &value) {
        const auto it = find(value);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const value_type &value) const {
        const auto it = find(value);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &value) {
        const auto it = find(value);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &value) const {
        const auto it = find(value);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given value.
     * @param value Value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const value_type &value) const {
        return (find(value) != cend());
    }

    /**
     * @brief Checks if the container contains an element that compares
     * _equivalent_ to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &value) const {
        return (find(value) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given element.
     * @param value The value of the element to examine.
     * @return The bucket for the given element.
     */
    [[nodiscard]] size_type bucket(const value_type &value) const {
        return value_to_bucket(value);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = value_to_bucket(packed.first()[pos].second);
                packed.first()[pos].first = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the elements.
     * @return The function used to hash the elements.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare elements for equality.
     * @return The function used to compare elements for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

#endif

// #include "core/algorithm.hpp"
#ifndef ENTT_CORE_ALGORITHM_HPP
#define ENTT_CORE_ALGORITHM_HPP

#include <algorithm>
#include <functional>
#include <iterator>
#include <utility>
#include <vector>
// #include "utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif


namespace entt {

/**
 * @brief Function object to wrap `std::sort` in a class type.
 *
 * Unfortunately, `std::sort` cannot be passed as template argument to a class
 * template or a function template.<br/>
 * This class fills the gap by wrapping some flavors of `std::sort` in a
 * function object.
 */
struct std_sort {
    /**
     * @brief Sorts the elements in a range.
     *
     * Sorts the elements in a range using the given binary comparison function.
     *
     * @tparam It Type of random access iterator.
     * @tparam Compare Type of comparison function object.
     * @tparam Args Types of arguments to forward to the sort function.
     * @param first An iterator to the first element of the range to sort.
     * @param last An iterator past the last element of the range to sort.
     * @param compare A valid comparison function object.
     * @param args Arguments to forward to the sort function, if any.
     */
    template<typename It, typename Compare = std::less<>, typename... Args>
    void operator()(It first, It last, Compare compare = Compare{}, Args &&...args) const {
        std::sort(std::forward<Args>(args)..., std::move(first), std::move(last), std::move(compare));
    }
};

/*! @brief Function object for performing insertion sort. */
struct insertion_sort {
    /**
     * @brief Sorts the elements in a range.
     *
     * Sorts the elements in a range using the given binary comparison function.
     *
     * @tparam It Type of random access iterator.
     * @tparam Compare Type of comparison function object.
     * @param first An iterator to the first element of the range to sort.
     * @param last An iterator past the last element of the range to sort.
     * @param compare A valid comparison function object.
     */
    template<typename It, typename Compare = std::less<>>
    void operator()(It first, It last, Compare compare = Compare{}) const {
        if(first < last) {
            for(auto it = first + 1; it < last; ++it) {
                auto value = std::move(*it);
                auto pre = it;

                for(; pre > first && compare(value, *(pre - 1)); --pre) {
                    *pre = std::move(*(pre - 1));
                }

                *pre = std::move(value);
            }
        }
    }
};

/**
 * @brief Function object for performing LSD radix sort.
 * @tparam Bit Number of bits processed per pass.
 * @tparam N Maximum number of bits to sort.
 */
template<std::size_t Bit, std::size_t N>
struct radix_sort {
    static_assert((N % Bit) == 0, "The maximum number of bits to sort must be a multiple of the number of bits processed per pass");

    /**
     * @brief Sorts the elements in a range.
     *
     * Sorts the elements in a range using the given _getter_ to access the
     * actual data to be sorted.
     *
     * This implementation is inspired by the online book
     * [Physically Based Rendering](http://www.pbr-book.org/3ed-2018/Primitives_and_Intersection_Acceleration/Bounding_Volume_Hierarchies.html#RadixSort).
     *
     * @tparam It Type of random access iterator.
     * @tparam Getter Type of _getter_ function object.
     * @param first An iterator to the first element of the range to sort.
     * @param last An iterator past the last element of the range to sort.
     * @param getter A valid _getter_ function object.
     */
    template<typename It, typename Getter = identity>
    void operator()(It first, It last, Getter getter = Getter{}) const {
        if(first < last) {
            static constexpr auto mask = (1 << Bit) - 1;
            static constexpr auto buckets = 1 << Bit;
            static constexpr auto passes = N / Bit;

            using value_type = typename std::iterator_traits<It>::value_type;
            std::vector<value_type> aux(std::distance(first, last));

            auto part = [getter = std::move(getter)](auto from, auto to, auto out, auto start) {
                std::size_t index[buckets]{};
                std::size_t count[buckets]{};

                for(auto it = from; it != to; ++it) {
                    ++count[(getter(*it) >> start) & mask];
                }

                for(std::size_t pos{}, end = buckets - 1u; pos < end; ++pos) {
                    index[pos + 1u] = index[pos] + count[pos];
                }

                for(auto it = from; it != to; ++it) {
                    out[index[(getter(*it) >> start) & mask]++] = std::move(*it);
                }
            };

            for(std::size_t pass = 0; pass < (passes & ~1); pass += 2) {
                part(first, last, aux.begin(), pass * Bit);
                part(aux.begin(), aux.end(), first, (pass + 1) * Bit);
            }

            if constexpr(passes & 1) {
                part(first, last, aux.begin(), (passes - 1) * Bit);
                std::move(aux.begin(), aux.end(), first);
            }
        }
    }
};

} // namespace entt

#endif

// #include "core/any.hpp"
#ifndef ENTT_CORE_ANY_HPP
#define ENTT_CORE_ANY_HPP

#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif

// #include "type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"
#ifndef ENTT_CORE_ATTRIBUTE_H
#define ENTT_CORE_ATTRIBUTE_H

#ifndef ENTT_EXPORT
#    if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
#        define ENTT_EXPORT __declspec(dllexport)
#        define ENTT_IMPORT __declspec(dllimport)
#        define ENTT_HIDDEN
#    elif defined __GNUC__ && __GNUC__ >= 4
#        define ENTT_EXPORT __attribute__((visibility("default")))
#        define ENTT_IMPORT __attribute__((visibility("default")))
#        define ENTT_HIDDEN __attribute__((visibility("hidden")))
#    else /* Unsupported compiler */
#        define ENTT_EXPORT
#        define ENTT_IMPORT
#        define ENTT_HIDDEN
#    endif
#endif

#ifndef ENTT_API
#    if defined ENTT_API_EXPORT
#        define ENTT_API ENTT_EXPORT
#    elif defined ENTT_API_IMPORT
#        define ENTT_API ENTT_IMPORT
#    else /* No API */
#        define ENTT_API
#    endif
#endif

#endif

// #include "fwd.hpp"

// #include "hashed_string.hpp"
#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP

#include <cstddef>
#include <cstdint>
// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename>
struct fnv1a_traits;

template<>
struct fnv1a_traits<std::uint32_t> {
    using type = std::uint32_t;
    static constexpr std::uint32_t offset = 2166136261;
    static constexpr std::uint32_t prime = 16777619;
};

template<>
struct fnv1a_traits<std::uint64_t> {
    using type = std::uint64_t;
    static constexpr std::uint64_t offset = 14695981039346656037ull;
    static constexpr std::uint64_t prime = 1099511628211ull;
};

template<typename Char>
struct basic_hashed_string {
    using value_type = Char;
    using size_type = std::size_t;
    using hash_type = id_type;

    const value_type *repr;
    size_type length;
    hash_type hash;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Zero overhead unique identifier.
 *
 * A hashed string is a compile-time tool that allows users to use
 * human-readable identifiers in the codebase while using their numeric
 * counterparts at runtime.<br/>
 * Because of that, a hashed string can also be used in constant expressions if
 * required.
 *
 * @warning
 * This class doesn't take ownership of user-supplied strings nor does it make a
 * copy of them.
 *
 * @tparam Char Character type.
 */
template<typename Char>
class basic_hashed_string: internal::basic_hashed_string<Char> {
    using base_type = internal::basic_hashed_string<Char>;
    using hs_traits = internal::fnv1a_traits<id_type>;

    struct const_wrapper {
        // non-explicit constructor on purpose
        constexpr const_wrapper(const Char *str) noexcept
            : repr{str} {}

        const Char *repr;
    };

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str) noexcept {
        base_type base{str, 0u, hs_traits::offset};

        for(; str[base.length]; ++base.length) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[base.length])) * hs_traits::prime;
        }

        return base;
    }

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str, const std::size_t len) noexcept {
        base_type base{str, len, hs_traits::offset};

        for(size_type pos{}; pos < len; ++pos) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[pos])) * hs_traits::prime;
        }

        return base;
    }

public:
    /*! @brief Character type. */
    using value_type = typename base_type::value_type;
    /*! @brief Unsigned integer type. */
    using size_type = typename base_type::size_type;
    /*! @brief Unsigned integer type. */
    using hash_type = typename base_type::hash_type;

    /**
     * @brief Returns directly the numeric representation of a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const value_type *str, const size_type len) noexcept {
        return basic_hashed_string{str, len};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     * @return The numeric representation of the string.
     */
    template<std::size_t N>
    [[nodiscard]] static constexpr hash_type value(const value_type (&str)[N]) noexcept {
        return basic_hashed_string{str};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @param wrapper Helps achieving the purpose by relying on overloading.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const_wrapper wrapper) noexcept {
        return basic_hashed_string{wrapper};
    }

    /*! @brief Constructs an empty hashed string. */
    constexpr basic_hashed_string() noexcept
        : base_type{} {}

    /**
     * @brief Constructs a hashed string from a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     */
    constexpr basic_hashed_string(const value_type *str, const size_type len) noexcept
        : base_type{helper(str, len)} {}

    /**
     * @brief Constructs a hashed string from an array of const characters.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     */
    template<std::size_t N>
    constexpr basic_hashed_string(const value_type (&str)[N]) noexcept
        : base_type{helper(str)} {}

    /**
     * @brief Explicit constructor on purpose to avoid constructing a hashed
     * string directly from a `const value_type *`.
     *
     * @warning
     * The lifetime of the string is not extended nor is it copied.
     *
     * @param wrapper Helps achieving the purpose by relying on overloading.
     */
    explicit constexpr basic_hashed_string(const_wrapper wrapper) noexcept
        : base_type{helper(wrapper.repr)} {}

    /**
     * @brief Returns the size a hashed string.
     * @return The size of the hashed string.
     */
    [[nodiscard]] constexpr size_type size() const noexcept {
        return base_type::length;
    }

    /**
     * @brief Returns the human-readable representation of a hashed string.
     * @return The string used to initialize the hashed string.
     */
    [[nodiscard]] constexpr const value_type *data() const noexcept {
        return base_type::repr;
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr hash_type value() const noexcept {
        return base_type::hash;
    }

    /*! @copydoc data */
    [[nodiscard]] constexpr operator const value_type *() const noexcept {
        return data();
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr operator hash_type() const noexcept {
        return value();
    }
};

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @param str Human-readable identifier.
 * @param len Length of the string to hash.
 */
template<typename Char>
basic_hashed_string(const Char *str, const std::size_t len) -> basic_hashed_string<Char>;

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @tparam N Number of characters of the identifier.
 * @param str Human-readable identifier.
 */
template<typename Char, std::size_t N>
basic_hashed_string(const Char (&str)[N]) -> basic_hashed_string<Char>;

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings are identical, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator==(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() == rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings differ, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than the second, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() < rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs < rhs);
}

/*! @brief Aliases for common character types. */
using hashed_string = basic_hashed_string<char>;

/*! @brief Aliases for common character types. */
using hashed_wstring = basic_hashed_string<wchar_t>;

inline namespace literals {

/**
 * @brief User defined literal for hashed strings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed string.
 */
[[nodiscard]] constexpr hashed_string operator"" _hs(const char *str, std::size_t) noexcept {
    return hashed_string{str};
}

/**
 * @brief User defined literal for hashed wstrings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed wstring.
 */
[[nodiscard]] constexpr hashed_wstring operator"" _hws(const wchar_t *str, std::size_t) noexcept {
    return hashed_wstring{str};
}

} // namespace literals

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

enum class any_operation : std::uint8_t {
    copy,
    move,
    transfer,
    assign,
    destroy,
    compare,
    get
};

enum class any_policy : std::uint8_t {
    owner,
    ref,
    cref
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A SBO friendly, type-safe container for single values of any type.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 */
template<std::size_t Len, std::size_t Align>
class basic_any {
    using operation = internal::any_operation;
    using policy = internal::any_policy;
    using vtable_type = const void *(const operation, const basic_any &, const void *);

    struct storage_type {
        alignas(Align) std::byte data[Len + !Len];
    };

    template<typename Type>
    static constexpr bool in_situ = Len && alignof(Type) <= Align && sizeof(Type) <= Len &&std::is_nothrow_move_constructible_v<Type>;

    template<typename Type>
    static const void *basic_vtable(const operation op, const basic_any &value, const void *other) {
        static_assert(!std::is_same_v<Type, void> && std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, Type>, "Invalid type");
        const Type *element = nullptr;

        if constexpr(in_situ<Type>) {
            element = value.owner() ? reinterpret_cast<const Type *>(&value.storage) : static_cast<const Type *>(value.instance);
        } else {
            element = static_cast<const Type *>(value.instance);
        }

        switch(op) {
        case operation::copy:
            if constexpr(std::is_copy_constructible_v<Type>) {
                static_cast<basic_any *>(const_cast<void *>(other))->initialize<Type>(*element);
            }
            break;
        case operation::move:
            if constexpr(in_situ<Type>) {
                if(value.owner()) {
                    return new(&static_cast<basic_any *>(const_cast<void *>(other))->storage) Type{std::move(*const_cast<Type *>(element))};
                }
            }

            return (static_cast<basic_any *>(const_cast<void *>(other))->instance = std::exchange(const_cast<basic_any &>(value).instance, nullptr));
        case operation::transfer:
            if constexpr(std::is_move_assignable_v<Type>) {
                *const_cast<Type *>(element) = std::move(*static_cast<Type *>(const_cast<void *>(other)));
                return other;
            }
            [[fallthrough]];
        case operation::assign:
            if constexpr(std::is_copy_assignable_v<Type>) {
                *const_cast<Type *>(element) = *static_cast<const Type *>(other);
                return other;
            }
            break;
        case operation::destroy:
            if constexpr(in_situ<Type>) {
                element->~Type();
            } else if constexpr(std::is_array_v<Type>) {
                delete[] element;
            } else {
                delete element;
            }
            break;
        case operation::compare:
            if constexpr(!std::is_function_v<Type> && !std::is_array_v<Type> && is_equality_comparable_v<Type>) {
                return *element == *static_cast<const Type *>(other) ? other : nullptr;
            } else {
                return (element == other) ? other : nullptr;
            }
        case operation::get:
            return element;
        }

        return nullptr;
    }

    template<typename Type, typename... Args>
    void initialize([[maybe_unused]] Args &&...args) {
        info = &type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();

        if constexpr(!std::is_void_v<Type>) {
            vtable = basic_vtable<std::remove_cv_t<std::remove_reference_t<Type>>>;

            if constexpr(std::is_lvalue_reference_v<Type>) {
                static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
                mode = std::is_const_v<std::remove_reference_t<Type>> ? policy::cref : policy::ref;
                instance = (std::addressof(args), ...);
            } else if constexpr(in_situ<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                if constexpr(sizeof...(Args) != 0u && std::is_aggregate_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                    new(&storage) std::remove_cv_t<std::remove_reference_t<Type>>{std::forward<Args>(args)...};
                } else {
                    new(&storage) std::remove_cv_t<std::remove_reference_t<Type>>(std::forward<Args>(args)...);
                }
            } else {
                if constexpr(sizeof...(Args) != 0u && std::is_aggregate_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                    instance = new std::remove_cv_t<std::remove_reference_t<Type>>{std::forward<Args>(args)...};
                } else {
                    instance = new std::remove_cv_t<std::remove_reference_t<Type>>(std::forward<Args>(args)...);
                }
            }
        }
    }

    basic_any(const basic_any &other, const policy pol) noexcept
        : instance{other.data()},
          info{other.info},
          vtable{other.vtable},
          mode{pol} {}

public:
    /*! @brief Size of the internal storage. */
    static constexpr auto length = Len;
    /*! @brief Alignment requirement. */
    static constexpr auto alignment = Align;

    /*! @brief Default constructor. */
    constexpr basic_any() noexcept
        : basic_any{std::in_place_type<void>} {}

    /**
     * @brief Constructs a wrapper by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit basic_any(std::in_place_type_t<Type>, Args &&...args)
        : instance{},
          info{},
          vtable{},
          mode{policy::owner} {
        initialize<Type>(std::forward<Args>(args)...);
    }

    /**
     * @brief Constructs a wrapper from a given value.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
    basic_any(Type &&value)
        : basic_any{std::in_place_type<std::decay_t<Type>>, std::forward<Type>(value)} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    basic_any(const basic_any &other)
        : basic_any{} {
        if(other.vtable) {
            other.vtable(operation::copy, other, this);
        }
    }

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_any(basic_any &&other) noexcept
        : instance{},
          info{other.info},
          vtable{other.vtable},
          mode{other.mode} {
        if(other.vtable) {
            other.vtable(operation::move, other, this);
        }
    }

    /*! @brief Frees the internal storage, whatever it means. */
    ~basic_any() {
        if(vtable && owner()) {
            vtable(operation::destroy, *this, nullptr);
        }
    }

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This any object.
     */
    basic_any &operator=(const basic_any &other) {
        reset();

        if(other.vtable) {
            other.vtable(operation::copy, other, this);
        }

        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This any object.
     */
    basic_any &operator=(basic_any &&other) noexcept {
        reset();

        if(other.vtable) {
            other.vtable(operation::move, other, this);
            info = other.info;
            vtable = other.vtable;
            mode = other.mode;
        }

        return *this;
    }

    /**
     * @brief Value assignment operator.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     * @return This any object.
     */
    template<typename Type>
    std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any &>
    operator=(Type &&value) {
        emplace<std::decay_t<Type>>(std::forward<Type>(value));
        return *this;
    }

    /**
     * @brief Returns the object type if any, `type_id<void>()` otherwise.
     * @return The object type if any, `type_id<void>()` otherwise.
     */
    [[nodiscard]] const type_info &type() const noexcept {
        return *info;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data() const noexcept {
        return vtable ? vtable(operation::get, *this, nullptr) : nullptr;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @param req Expected type.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data(const type_info &req) const noexcept {
        return *info == req ? data() : nullptr;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] void *data() noexcept {
        return mode == policy::cref ? nullptr : const_cast<void *>(std::as_const(*this).data());
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @param req Expected type.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] void *data(const type_info &req) noexcept {
        return mode == policy::cref ? nullptr : const_cast<void *>(std::as_const(*this).data(req));
    }

    /**
     * @brief Replaces the contained object by creating a new instance directly.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    void emplace(Args &&...args) {
        reset();
        initialize<Type>(std::forward<Args>(args)...);
    }

    /**
     * @brief Assigns a value to the contained object without replacing it.
     * @param other The value to assign to the contained object.
     * @return True in case of success, false otherwise.
     */
    bool assign(const basic_any &other) {
        if(vtable && mode != policy::cref && *info == *other.info) {
            return (vtable(operation::assign, *this, other.data()) != nullptr);
        }

        return false;
    }

    /*! @copydoc assign */
    bool assign(basic_any &&other) {
        if(vtable && mode != policy::cref && *info == *other.info) {
            if(auto *val = other.data(); val) {
                return (vtable(operation::transfer, *this, val) != nullptr);
            } else {
                return (vtable(operation::assign, *this, std::as_const(other).data()) != nullptr);
            }
        }

        return false;
    }

    /*! @brief Destroys contained object */
    void reset() {
        if(vtable && owner()) {
            vtable(operation::destroy, *this, nullptr);
        }

        // unnecessary but it helps to detect nasty bugs
        ENTT_ASSERT((instance = nullptr) == nullptr, "");
        info = &type_id<void>();
        vtable = nullptr;
        mode = policy::owner;
    }

    /**
     * @brief Returns false if a wrapper is empty, true otherwise.
     * @return False if the wrapper is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return vtable != nullptr;
    }

    /**
     * @brief Checks if two wrappers differ in their content.
     * @param other Wrapper with which to compare.
     * @return False if the two objects differ in their content, true otherwise.
     */
    [[nodiscard]] bool operator==(const basic_any &other) const noexcept {
        if(vtable && *info == *other.info) {
            return (vtable(operation::compare, *this, other.data()) != nullptr);
        }

        return (!vtable && !other.vtable);
    }

    /**
     * @brief Checks if two wrappers differ in their content.
     * @param other Wrapper with which to compare.
     * @return True if the two objects differ in their content, false otherwise.
     */
    [[nodiscard]] bool operator!=(const basic_any &other) const noexcept {
        return !(*this == other);
    }

    /**
     * @brief Aliasing constructor.
     * @return A wrapper that shares a reference to an unmanaged object.
     */
    [[nodiscard]] basic_any as_ref() noexcept {
        return basic_any{*this, (mode == policy::cref ? policy::cref : policy::ref)};
    }

    /*! @copydoc as_ref */
    [[nodiscard]] basic_any as_ref() const noexcept {
        return basic_any{*this, policy::cref};
    }

    /**
     * @brief Returns true if a wrapper owns its object, false otherwise.
     * @return True if the wrapper owns its object, false otherwise.
     */
    [[nodiscard]] bool owner() const noexcept {
        return (mode == policy::owner);
    }

private:
    union {
        const void *instance;
        storage_type storage;
    };
    const type_info *info;
    vtable_type *vtable;
    policy mode;
};

/**
 * @brief Performs type-safe access to the contained object.
 * @tparam Type Type to which conversion is required.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Alignment requirement.
 * @param data Target any object.
 * @return The element converted to the requested type.
 */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(const basic_any<Len, Align> &data) noexcept {
    const auto *const instance = any_cast<std::remove_reference_t<Type>>(&data);
    ENTT_ASSERT(instance, "Invalid instance");
    return static_cast<Type>(*instance);
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(basic_any<Len, Align> &data) noexcept {
    // forces const on non-reference types to make them work also with wrappers for const references
    auto *const instance = any_cast<std::remove_reference_t<const Type>>(&data);
    ENTT_ASSERT(instance, "Invalid instance");
    return static_cast<Type>(*instance);
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(basic_any<Len, Align> &&data) noexcept {
    if constexpr(std::is_copy_constructible_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
        if(auto *const instance = any_cast<std::remove_reference_t<Type>>(&data); instance) {
            return static_cast<Type>(std::move(*instance));
        } else {
            return any_cast<Type>(data);
        }
    } else {
        auto *const instance = any_cast<std::remove_reference_t<Type>>(&data);
        ENTT_ASSERT(instance, "Invalid instance");
        return static_cast<Type>(std::move(*instance));
    }
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
const Type *any_cast(const basic_any<Len, Align> *data) noexcept {
    const auto &info = type_id<std::remove_cv_t<Type>>();
    return static_cast<const Type *>(data->data(info));
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type *any_cast(basic_any<Len, Align> *data) noexcept {
    if constexpr(std::is_const_v<Type>) {
        // last attempt to make wrappers for const references return their values
        return any_cast<Type>(&std::as_const(*data));
    } else {
        const auto &info = type_id<std::remove_cv_t<Type>>();
        return static_cast<Type *>(data->data(info));
    }
}

/**
 * @brief Constructs a wrapper from a given type, passing it all arguments.
 * @tparam Type Type of object to use to initialize the wrapper.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 * @tparam Args Types of arguments to use to construct the new instance.
 * @param args Parameters to use to construct the instance.
 * @return A properly initialized wrapper for an object of the given type.
 */
template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
basic_any<Len, Align> make_any(Args &&...args) {
    return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
}

/**
 * @brief Forwards its argument and avoids copies for lvalue references.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 * @tparam Type Type of argument to use to construct the new instance.
 * @param value Parameter to use to construct the instance.
 * @return A properly initialized and not necessarily owning wrapper.
 */
template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
basic_any<Len, Align> forward_as_any(Type &&value) {
    return basic_any<Len, Align>{std::in_place_type<Type &&>, std::forward<Type>(value)};
}

} // namespace entt

#endif

// #include "core/attribute.h"
#ifndef ENTT_CORE_ATTRIBUTE_H
#define ENTT_CORE_ATTRIBUTE_H

#ifndef ENTT_EXPORT
#    if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
#        define ENTT_EXPORT __declspec(dllexport)
#        define ENTT_IMPORT __declspec(dllimport)
#        define ENTT_HIDDEN
#    elif defined __GNUC__ && __GNUC__ >= 4
#        define ENTT_EXPORT __attribute__((visibility("default")))
#        define ENTT_IMPORT __attribute__((visibility("default")))
#        define ENTT_HIDDEN __attribute__((visibility("hidden")))
#    else /* Unsupported compiler */
#        define ENTT_EXPORT
#        define ENTT_IMPORT
#        define ENTT_HIDDEN
#    endif
#endif

#ifndef ENTT_API
#    if defined ENTT_API_EXPORT
#        define ENTT_API ENTT_EXPORT
#    elif defined ENTT_API_IMPORT
#        define ENTT_API ENTT_IMPORT
#    else /* No API */
#        define ENTT_API
#    endif
#endif

#endif

// #include "core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "core/enum.hpp"
#ifndef ENTT_CORE_ENUM_HPP
#define ENTT_CORE_ENUM_HPP

#include <type_traits>

namespace entt {

/**
 * @brief Enable bitmask support for enum classes.
 * @tparam Type The enum type for which to enable bitmask support.
 */
template<typename Type, typename = void>
struct enum_as_bitmask: std::false_type {};

/*! @copydoc enum_as_bitmask */
template<typename Type>
struct enum_as_bitmask<Type, std::void_t<decltype(Type::_entt_enum_as_bitmask)>>: std::is_enum<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The enum class type for which to enable bitmask support.
 */
template<typename Type>
inline constexpr bool enum_as_bitmask_v = enum_as_bitmask<Type>::value;

} // namespace entt

/**
 * @brief Operator available for enums for which bitmask support is enabled.
 * @tparam Type Enum class type.
 * @param lhs The first value to use.
 * @param rhs The second value to use.
 * @return The result of invoking the operator on the underlying types of the
 * two values provided.
 */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type>
operator|(const Type lhs, const Type rhs) noexcept {
    return static_cast<Type>(static_cast<std::underlying_type_t<Type>>(lhs) | static_cast<std::underlying_type_t<Type>>(rhs));
}

/*! @copydoc operator| */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type>
operator&(const Type lhs, const Type rhs) noexcept {
    return static_cast<Type>(static_cast<std::underlying_type_t<Type>>(lhs) & static_cast<std::underlying_type_t<Type>>(rhs));
}

/*! @copydoc operator| */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type>
operator^(const Type lhs, const Type rhs) noexcept {
    return static_cast<Type>(static_cast<std::underlying_type_t<Type>>(lhs) ^ static_cast<std::underlying_type_t<Type>>(rhs));
}

/**
 * @brief Operator available for enums for which bitmask support is enabled.
 * @tparam Type Enum class type.
 * @param value The value to use.
 * @return The result of invoking the operator on the underlying types of the
 * value provided.
 */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type>
operator~(const Type value) noexcept {
    return static_cast<Type>(~static_cast<std::underlying_type_t<Type>>(value));
}

/*! @copydoc operator~ */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, bool>
operator!(const Type value) noexcept {
    return !static_cast<std::underlying_type_t<Type>>(value);
}

/*! @copydoc operator| */
template<typename Type>
constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type &>
operator|=(Type &lhs, const Type rhs) noexcept {
    return (lhs = (lhs | rhs));
}

/*! @copydoc operator| */
template<typename Type>
constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type &>
operator&=(Type &lhs, const Type rhs) noexcept {
    return (lhs = (lhs & rhs));
}

/*! @copydoc operator| */
template<typename Type>
constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type &>
operator^=(Type &lhs, const Type rhs) noexcept {
    return (lhs = (lhs ^ rhs));
}

#endif

// #include "core/family.hpp"
#ifndef ENTT_CORE_FAMILY_HPP
#define ENTT_CORE_FAMILY_HPP

// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Dynamic identifier generator.
 *
 * Utility class template that can be used to assign unique identifiers to types
 * at runtime. Use different specializations to create separate sets of
 * identifiers.
 */
template<typename...>
class family {
    inline static ENTT_MAYBE_ATOMIC(id_type) identifier{};

public:
    /*! @brief Unsigned integer type. */
    using value_type = id_type;

    /*! @brief Statically generated unique identifier for the given type. */
    template<typename... Type>
    // at the time I'm writing, clang crashes during compilation if auto is used instead of family_type
    inline static const value_type value = identifier++;
};

} // namespace entt

#endif

// #include "core/hashed_string.hpp"
#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP

#include <cstddef>
#include <cstdint>
// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename>
struct fnv1a_traits;

template<>
struct fnv1a_traits<std::uint32_t> {
    using type = std::uint32_t;
    static constexpr std::uint32_t offset = 2166136261;
    static constexpr std::uint32_t prime = 16777619;
};

template<>
struct fnv1a_traits<std::uint64_t> {
    using type = std::uint64_t;
    static constexpr std::uint64_t offset = 14695981039346656037ull;
    static constexpr std::uint64_t prime = 1099511628211ull;
};

template<typename Char>
struct basic_hashed_string {
    using value_type = Char;
    using size_type = std::size_t;
    using hash_type = id_type;

    const value_type *repr;
    size_type length;
    hash_type hash;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Zero overhead unique identifier.
 *
 * A hashed string is a compile-time tool that allows users to use
 * human-readable identifiers in the codebase while using their numeric
 * counterparts at runtime.<br/>
 * Because of that, a hashed string can also be used in constant expressions if
 * required.
 *
 * @warning
 * This class doesn't take ownership of user-supplied strings nor does it make a
 * copy of them.
 *
 * @tparam Char Character type.
 */
template<typename Char>
class basic_hashed_string: internal::basic_hashed_string<Char> {
    using base_type = internal::basic_hashed_string<Char>;
    using hs_traits = internal::fnv1a_traits<id_type>;

    struct const_wrapper {
        // non-explicit constructor on purpose
        constexpr const_wrapper(const Char *str) noexcept
            : repr{str} {}

        const Char *repr;
    };

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str) noexcept {
        base_type base{str, 0u, hs_traits::offset};

        for(; str[base.length]; ++base.length) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[base.length])) * hs_traits::prime;
        }

        return base;
    }

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str, const std::size_t len) noexcept {
        base_type base{str, len, hs_traits::offset};

        for(size_type pos{}; pos < len; ++pos) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[pos])) * hs_traits::prime;
        }

        return base;
    }

public:
    /*! @brief Character type. */
    using value_type = typename base_type::value_type;
    /*! @brief Unsigned integer type. */
    using size_type = typename base_type::size_type;
    /*! @brief Unsigned integer type. */
    using hash_type = typename base_type::hash_type;

    /**
     * @brief Returns directly the numeric representation of a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const value_type *str, const size_type len) noexcept {
        return basic_hashed_string{str, len};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     * @return The numeric representation of the string.
     */
    template<std::size_t N>
    [[nodiscard]] static constexpr hash_type value(const value_type (&str)[N]) noexcept {
        return basic_hashed_string{str};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @param wrapper Helps achieving the purpose by relying on overloading.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const_wrapper wrapper) noexcept {
        return basic_hashed_string{wrapper};
    }

    /*! @brief Constructs an empty hashed string. */
    constexpr basic_hashed_string() noexcept
        : base_type{} {}

    /**
     * @brief Constructs a hashed string from a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     */
    constexpr basic_hashed_string(const value_type *str, const size_type len) noexcept
        : base_type{helper(str, len)} {}

    /**
     * @brief Constructs a hashed string from an array of const characters.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     */
    template<std::size_t N>
    constexpr basic_hashed_string(const value_type (&str)[N]) noexcept
        : base_type{helper(str)} {}

    /**
     * @brief Explicit constructor on purpose to avoid constructing a hashed
     * string directly from a `const value_type *`.
     *
     * @warning
     * The lifetime of the string is not extended nor is it copied.
     *
     * @param wrapper Helps achieving the purpose by relying on overloading.
     */
    explicit constexpr basic_hashed_string(const_wrapper wrapper) noexcept
        : base_type{helper(wrapper.repr)} {}

    /**
     * @brief Returns the size a hashed string.
     * @return The size of the hashed string.
     */
    [[nodiscard]] constexpr size_type size() const noexcept {
        return base_type::length;
    }

    /**
     * @brief Returns the human-readable representation of a hashed string.
     * @return The string used to initialize the hashed string.
     */
    [[nodiscard]] constexpr const value_type *data() const noexcept {
        return base_type::repr;
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr hash_type value() const noexcept {
        return base_type::hash;
    }

    /*! @copydoc data */
    [[nodiscard]] constexpr operator const value_type *() const noexcept {
        return data();
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr operator hash_type() const noexcept {
        return value();
    }
};

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @param str Human-readable identifier.
 * @param len Length of the string to hash.
 */
template<typename Char>
basic_hashed_string(const Char *str, const std::size_t len) -> basic_hashed_string<Char>;

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @tparam N Number of characters of the identifier.
 * @param str Human-readable identifier.
 */
template<typename Char, std::size_t N>
basic_hashed_string(const Char (&str)[N]) -> basic_hashed_string<Char>;

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings are identical, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator==(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() == rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings differ, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than the second, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() < rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs < rhs);
}

/*! @brief Aliases for common character types. */
using hashed_string = basic_hashed_string<char>;

/*! @brief Aliases for common character types. */
using hashed_wstring = basic_hashed_string<wchar_t>;

inline namespace literals {

/**
 * @brief User defined literal for hashed strings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed string.
 */
[[nodiscard]] constexpr hashed_string operator"" _hs(const char *str, std::size_t) noexcept {
    return hashed_string{str};
}

/**
 * @brief User defined literal for hashed wstrings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed wstring.
 */
[[nodiscard]] constexpr hashed_wstring operator"" _hws(const wchar_t *str, std::size_t) noexcept {
    return hashed_wstring{str};
}

} // namespace literals

} // namespace entt

#endif

// #include "core/ident.hpp"
#ifndef ENTT_CORE_IDENT_HPP
#define ENTT_CORE_IDENT_HPP

#include <cstddef>
#include <type_traits>
#include <utility>
// #include "fwd.hpp"

// #include "type_traits.hpp"


namespace entt {

/**
 * @brief Type integral identifiers.
 * @tparam Type List of types for which to generate identifiers.
 */
template<typename... Type>
class ident {
    template<typename Curr, std::size_t... Index>
    [[nodiscard]] static constexpr id_type get(std::index_sequence<Index...>) noexcept {
        static_assert((std::is_same_v<Curr, Type> || ...), "Invalid type");
        return (0 + ... + (std::is_same_v<Curr, type_list_element_t<Index, type_list<std::decay_t<Type>...>>> ? id_type{Index} : id_type{}));
    }

public:
    /*! @brief Unsigned integer type. */
    using value_type = id_type;

    /*! @brief Statically generated unique identifier for the given type. */
    template<typename Curr>
    static constexpr value_type value = get<std::decay_t<Curr>>(std::index_sequence_for<Type...>{});
};

} // namespace entt

#endif

// #include "core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "core/monostate.hpp"
#ifndef ENTT_CORE_MONOSTATE_HPP
#define ENTT_CORE_MONOSTATE_HPP

// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Minimal implementation of the monostate pattern.
 *
 * A minimal, yet complete configuration system built on top of the monostate
 * pattern. Thread safe by design, it works only with basic types like `int`s or
 * `bool`s.<br/>
 * Multiple types and therefore more than one value can be associated with a
 * single key. Because of this, users must pay attention to use the same type
 * both during an assignment and when they try to read back their data.
 * Otherwise, they can incur in unexpected results.
 */
template<id_type>
struct monostate {
    /**
     * @brief Assigns a value of a specific type to a given key.
     * @tparam Type Type of the value to assign.
     * @param val User data to assign to the given key.
     */
    template<typename Type>
    void operator=(Type val) const noexcept {
        value<Type> = val;
    }

    /**
     * @brief Gets a value of a specific type for a given key.
     * @tparam Type Type of the value to get.
     * @return Stored value, if any.
     */
    template<typename Type>
    operator Type() const noexcept {
        return value<Type>;
    }

private:
    template<typename Type>
    inline static ENTT_MAYBE_ATOMIC(Type) value{};
};

/**
 * @brief Helper variable template.
 * @tparam Value Value used to differentiate between different variables.
 */
template<id_type Value>
inline monostate<Value> monostate_v = {};

} // namespace entt

#endif

// #include "core/tuple.hpp"
#ifndef ENTT_CORE_TUPLE_HPP
#define ENTT_CORE_TUPLE_HPP

#include <tuple>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename>
struct is_tuple_impl: std::false_type {};

template<typename... Args>
struct is_tuple_impl<std::tuple<Args...>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Provides the member constant `value` to true if a given type is a
 * tuple, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type>
struct is_tuple: internal::is_tuple_impl<std::remove_cv_t<Type>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_tuple_v = is_tuple<Type>::value;

/**
 * @brief Utility function to unwrap tuples of a single element.
 * @tparam Type Tuple type of any sizes.
 * @param value A tuple object of the given type.
 * @return The tuple itself if it contains more than one element, the first
 * element otherwise.
 */
template<typename Type>
constexpr decltype(auto) unwrap_tuple(Type &&value) noexcept {
    if constexpr(std::tuple_size_v<std::remove_reference_t<Type>> == 1u) {
        return std::get<0>(std::forward<Type>(value));
    } else {
        return std::forward<Type>(value);
    }
}

/**
 * @brief Utility class to forward-and-apply tuple objects.
 * @tparam Func Type of underlying invocable object.
 */
template<typename Func>
struct forward_apply: private Func {
    /**
     * @brief Constructs a forward-and-apply object.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<class... Args>
    constexpr forward_apply(Args &&...args) noexcept(std::is_nothrow_constructible_v<Func, Args...>)
        : Func{std::forward<Args>(args)...} {}

    /**
     * @brief Forwards and applies the arguments with the underlying function.
     * @tparam Type Tuple-like type to forward to the underlying function.
     * @param args Parameters to forward to the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class Type>
    constexpr decltype(auto) operator()(Type &&args) noexcept(noexcept(std::apply(std::declval<Func &>(), args))) {
        return std::apply(static_cast<Func &>(*this), std::forward<Type>(args));
    }

    /*! @copydoc operator()() */
    template<class Type>
    constexpr decltype(auto) operator()(Type &&args) const noexcept(noexcept(std::apply(std::declval<const Func &>(), args))) {
        return std::apply(static_cast<const Func &>(*this), std::forward<Type>(args));
    }
};

/**
 * @brief Deduction guide.
 * @tparam Func Type of underlying invocable object.
 */
template<typename Func>
forward_apply(Func) -> forward_apply<std::remove_reference_t<std::remove_cv_t<Func>>>;

} // namespace entt

#endif

// #include "core/type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"

// #include "fwd.hpp"

// #include "hashed_string.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "entity/component.hpp"
#ifndef ENTT_ENTITY_COMPONENT_HPP
#define ENTT_ENTITY_COMPONENT_HPP

#include <cstddef>
#include <type_traits>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, typename = void>
struct in_place_delete: std::bool_constant<!(std::is_move_constructible_v<Type> && std::is_move_assignable_v<Type>)> {};

template<typename Type>
struct in_place_delete<Type, std::enable_if_t<Type::in_place_delete>>
    : std::true_type {};

template<typename Type, typename = void>
struct page_size: std::integral_constant<std::size_t, !std::is_empty_v<ENTT_ETO_TYPE(Type)> * ENTT_PACKED_PAGE> {};

template<typename Type>
struct page_size<Type, std::enable_if_t<std::is_convertible_v<decltype(Type::page_size), std::size_t>>>
    : std::integral_constant<std::size_t, Type::page_size> {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Common way to access various properties of components.
 * @tparam Type Type of component.
 */
template<typename Type, typename = void>
struct component_traits {
    static_assert(std::is_same_v<std::decay_t<Type>, Type>, "Unsupported type");

    /*! @brief Component type. */
    using type = Type;

    /*! @brief Pointer stability, default is `false`. */
    static constexpr bool in_place_delete = internal::in_place_delete<Type>::value;
    /*! @brief Page size, default is `ENTT_PACKED_PAGE` for non-empty types. */
    static constexpr std::size_t page_size = internal::page_size<Type>::value;
};

/**
 * @brief Helper variable template.
 * @tparam Type Type of component.
 */
template<class Type>
inline constexpr bool ignore_as_empty_v = (std::is_void_v<Type> || component_traits<Type>::page_size == 0u);

} // namespace entt

#endif

// #include "entity/entity.hpp"
#ifndef ENTT_ENTITY_ENTITY_HPP
#define ENTT_ENTITY_ENTITY_HPP

#include <cstddef>
#include <cstdint>
#include <type_traits>
// #include "../config/config.h"

// #include "fwd.hpp"
#ifndef ENTT_ENTITY_FWD_HPP
#define ENTT_ENTITY_FWD_HPP

#include <memory>
#include <type_traits>
// #include "../core/fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/*! @brief Default entity identifier. */
enum class entity : id_type {};

template<typename Entity = entity, typename = std::allocator<Entity>>
class basic_sparse_set;

template<typename Type, typename = entity, typename = std::allocator<Type>, typename = void>
class basic_storage;

template<typename Type>
class sigh_storage_mixin;

/**
 * @brief Provides a common way to define storage types.
 * @tparam Type Storage value type.
 * @tparam Entity A valid entity type (see entt_traits for more details).
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Entity = entity, typename Allocator = std::allocator<Type>, typename = void>
struct storage_type {
    /*! @brief Type-to-storage conversion result. */
    using type = sigh_storage_mixin<basic_storage<Type, Entity, Allocator>>;
};

/**
 * @brief Helper type.
 * @tparam Args Arguments to forward.
 */
template<typename... Args>
using storage_type_t = typename storage_type<Args...>::type;

/**
 * Type-to-storage conversion utility that preserves constness.
 * @tparam Type Storage value type, eventually const.
 * @tparam Entity A valid entity type (see entt_traits for more details).
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Entity = entity, typename Allocator = std::allocator<std::remove_const_t<Type>>>
struct storage_for {
    /*! @brief Type-to-storage conversion result. */
    using type = constness_as_t<storage_type_t<std::remove_const_t<Type>, Entity, Allocator>, Type>;
};

/**
 * @brief Helper type.
 * @tparam Args Arguments to forward.
 */
template<typename... Args>
using storage_for_t = typename storage_for<Args...>::type;

template<typename Entity = entity, typename = std::allocator<Entity>>
class basic_registry;

template<typename, typename, typename = void>
class basic_view;

template<typename Type, typename = std::allocator<Type *>>
class basic_runtime_view;

template<typename, typename, typename>
class basic_group;

template<typename>
class basic_observer;

template<typename>
class basic_organizer;

template<typename, typename...>
struct basic_handle;

template<typename>
class basic_snapshot;

template<typename>
class basic_snapshot_loader;

template<typename>
class basic_continuous_loader;

/**
 * @brief Alias for exclusion lists.
 * @tparam Type List of types.
 */
template<typename... Type>
using exclude_t = type_list<Type...>;

/**
 * @brief Variable template for exclusion lists.
 * @tparam Type List of types.
 */
template<typename... Type>
inline constexpr exclude_t<Type...> exclude{};

/**
 * @brief Alias for lists of observed components.
 * @tparam Type List of types.
 */
template<typename... Type>
using get_t = type_list<Type...>;

/**
 * @brief Variable template for lists of observed components.
 * @tparam Type List of types.
 */
template<typename... Type>
inline constexpr get_t<Type...> get{};

/**
 * @brief Alias for lists of owned components.
 * @tparam Type List of types.
 */
template<typename... Type>
using owned_t = type_list<Type...>;

/**
 * @brief Variable template for lists of owned components.
 * @tparam Type List of types.
 */
template<typename... Type>
inline constexpr owned_t<Type...> owned{};

/*! @brief Alias declaration for the most common use case. */
using sparse_set = basic_sparse_set<>;

/**
 * @brief Alias declaration for the most common use case.
 * @tparam Type Type of objects assigned to the entities.
 */
template<typename Type>
using storage = basic_storage<Type>;

/*! @brief Alias declaration for the most common use case. */
using registry = basic_registry<>;

/*! @brief Alias declaration for the most common use case. */
using observer = basic_observer<registry>;

/*! @brief Alias declaration for the most common use case. */
using organizer = basic_organizer<registry>;

/*! @brief Alias declaration for the most common use case. */
using handle = basic_handle<registry>;

/*! @brief Alias declaration for the most common use case. */
using const_handle = basic_handle<const registry>;

/**
 * @brief Alias declaration for the most common use case.
 * @tparam Args Other template parameters.
 */
template<typename... Args>
using handle_view = basic_handle<registry, Args...>;

/**
 * @brief Alias declaration for the most common use case.
 * @tparam Args Other template parameters.
 */
template<typename... Args>
using const_handle_view = basic_handle<const registry, Args...>;

/*! @brief Alias declaration for the most common use case. */
using snapshot = basic_snapshot<registry>;

/*! @brief Alias declaration for the most common use case. */
using snapshot_loader = basic_snapshot_loader<registry>;

/*! @brief Alias declaration for the most common use case. */
using continuous_loader = basic_continuous_loader<registry>;

/**
 * @brief Alias declaration for the most common use case.
 * @tparam Get Types of storage iterated by the view.
 * @tparam Exclude Types of storage used to filter the view.
 */
template<typename Get, typename Exclude = exclude_t<>>
using view = basic_view<type_list_transform_t<Get, storage_for>, type_list_transform_t<Exclude, storage_for>>;

/*! @brief Alias declaration for the most common use case. */
using runtime_view = basic_runtime_view<sparse_set>;

/*! @brief Alias declaration for the most common use case. */
using const_runtime_view = basic_runtime_view<const sparse_set>;

/**
 * @brief Alias declaration for the most common use case.
 * @tparam Owned Types of storage _owned_ by the group.
 * @tparam Get Types of storage _observed_ by the group.
 * @tparam Exclude Types of storage used to filter the group.
 */
template<typename Owned, typename Get, typename Exclude>
using group = basic_group<type_list_transform_t<Owned, storage_for>, type_list_transform_t<Get, storage_for>, type_list_transform_t<Exclude, storage_for>>;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct entt_traits;

template<typename Type>
struct entt_traits<Type, std::enable_if_t<std::is_enum_v<Type>>>
    : entt_traits<std::underlying_type_t<Type>> {};

template<typename Type>
struct entt_traits<Type, std::enable_if_t<std::is_class_v<Type>>>
    : entt_traits<typename Type::entity_type> {};

template<>
struct entt_traits<std::uint32_t> {
    using entity_type = std::uint32_t;
    using version_type = std::uint16_t;

    static constexpr entity_type entity_mask = 0xFFFFF;
    static constexpr entity_type version_mask = 0xFFF;
    static constexpr std::size_t entity_shift = 20u;
};

template<>
struct entt_traits<std::uint64_t> {
    using entity_type = std::uint64_t;
    using version_type = std::uint32_t;

    static constexpr entity_type entity_mask = 0xFFFFFFFF;
    static constexpr entity_type version_mask = 0xFFFFFFFF;
    static constexpr std::size_t entity_shift = 32u;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Entity traits.
 * @tparam Type Type of identifier.
 */
template<typename Type>
class entt_traits: internal::entt_traits<Type> {
    using base_type = internal::entt_traits<Type>;

public:
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Underlying entity type. */
    using entity_type = typename base_type::entity_type;
    /*! @brief Underlying version type. */
    using version_type = typename base_type::version_type;
    /*! @brief Reserved identifier. */
    static constexpr entity_type reserved = base_type::entity_mask | (base_type::version_mask << base_type::entity_shift);
    /*! @brief Page size, default is `ENTT_SPARSE_PAGE`. */
    static constexpr auto page_size = ENTT_SPARSE_PAGE;

    /**
     * @brief Converts an entity to its underlying type.
     * @param value The value to convert.
     * @return The integral representation of the given value.
     */
    [[nodiscard]] static constexpr entity_type to_integral(const value_type value) noexcept {
        return static_cast<entity_type>(value);
    }

    /**
     * @brief Returns the entity part once converted to the underlying type.
     * @param value The value to convert.
     * @return The integral representation of the entity part.
     */
    [[nodiscard]] static constexpr entity_type to_entity(const value_type value) noexcept {
        return (to_integral(value) & base_type::entity_mask);
    }

    /**
     * @brief Returns the version part once converted to the underlying type.
     * @param value The value to convert.
     * @return The integral representation of the version part.
     */
    [[nodiscard]] static constexpr version_type to_version(const value_type value) noexcept {
        return (to_integral(value) >> base_type::entity_shift);
    }

    /**
     * @brief Constructs an identifier from its parts.
     *
     * If the version part is not provided, a tombstone is returned.<br/>
     * If the entity part is not provided, a null identifier is returned.
     *
     * @param entity The entity part of the identifier.
     * @param version The version part of the identifier.
     * @return A properly constructed identifier.
     */
    [[nodiscard]] static constexpr value_type construct(const entity_type entity, const version_type version) noexcept {
        return value_type{(entity & base_type::entity_mask) | (static_cast<entity_type>(version) << base_type::entity_shift)};
    }

    /**
     * @brief Combines two identifiers in a single one.
     *
     * The returned identifier is a copy of the first element except for its
     * version, which is taken from the second element.
     *
     * @param lhs The identifier from which to take the entity part.
     * @param rhs The identifier from which to take the version part.
     * @return A properly constructed identifier.
     */
    [[nodiscard]] static constexpr value_type combine(const entity_type lhs, const entity_type rhs) noexcept {
        constexpr auto mask = (base_type::version_mask << base_type::entity_shift);
        return value_type{(lhs & base_type::entity_mask) | (rhs & mask)};
    }
};

/**
 * @copydoc entt_traits<Entity>::to_integral
 * @tparam Entity The value type.
 */
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::entity_type to_integral(const Entity value) noexcept {
    return entt_traits<Entity>::to_integral(value);
}

/**
 * @copydoc entt_traits<Entity>::to_entity
 * @tparam Entity The value type.
 */
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::entity_type to_entity(const Entity value) noexcept {
    return entt_traits<Entity>::to_entity(value);
}

/**
 * @copydoc entt_traits<Entity>::to_version
 * @tparam Entity The value type.
 */
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::version_type to_version(const Entity value) noexcept {
    return entt_traits<Entity>::to_version(value);
}

/*! @brief Null object for all identifiers.  */
struct null_t {
    /**
     * @brief Converts the null object to identifiers of any type.
     * @tparam Entity Type of identifier.
     * @return The null representation for the given type.
     */
    template<typename Entity>
    [[nodiscard]] constexpr operator Entity() const noexcept {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::combine(entity_traits::reserved, entity_traits::reserved);
    }

    /**
     * @brief Compares two null objects.
     * @param other A null object.
     * @return True in all cases.
     */
    [[nodiscard]] constexpr bool operator==([[maybe_unused]] const null_t other) const noexcept {
        return true;
    }

    /**
     * @brief Compares two null objects.
     * @param other A null object.
     * @return False in all cases.
     */
    [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const null_t other) const noexcept {
        return false;
    }

    /**
     * @brief Compares a null object and an identifier of any type.
     * @tparam Entity Type of identifier.
     * @param entity Identifier with which to compare.
     * @return False if the two elements differ, true otherwise.
     */
    template<typename Entity>
    [[nodiscard]] constexpr bool operator==(const Entity entity) const noexcept {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::to_entity(entity) == entity_traits::to_entity(*this);
    }

    /**
     * @brief Compares a null object and an identifier of any type.
     * @tparam Entity Type of identifier.
     * @param entity Identifier with which to compare.
     * @return True if the two elements differ, false otherwise.
     */
    template<typename Entity>
    [[nodiscard]] constexpr bool operator!=(const Entity entity) const noexcept {
        return !(entity == *this);
    }
};

/**
 * @brief Compares a null object and an identifier of any type.
 * @tparam Entity Type of identifier.
 * @param entity Identifier with which to compare.
 * @param other A null object yet to be converted.
 * @return False if the two elements differ, true otherwise.
 */
template<typename Entity>
[[nodiscard]] constexpr bool operator==(const Entity entity, const null_t other) noexcept {
    return other.operator==(entity);
}

/**
 * @brief Compares a null object and an identifier of any type.
 * @tparam Entity Type of identifier.
 * @param entity Identifier with which to compare.
 * @param other A null object yet to be converted.
 * @return True if the two elements differ, false otherwise.
 */
template<typename Entity>
[[nodiscard]] constexpr bool operator!=(const Entity entity, const null_t other) noexcept {
    return !(other == entity);
}

/*! @brief Tombstone object for all identifiers.  */
struct tombstone_t {
    /**
     * @brief Converts the tombstone object to identifiers of any type.
     * @tparam Entity Type of identifier.
     * @return The tombstone representation for the given type.
     */
    template<typename Entity>
    [[nodiscard]] constexpr operator Entity() const noexcept {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::combine(entity_traits::reserved, entity_traits::reserved);
    }

    /**
     * @brief Compares two tombstone objects.
     * @param other A tombstone object.
     * @return True in all cases.
     */
    [[nodiscard]] constexpr bool operator==([[maybe_unused]] const tombstone_t other) const noexcept {
        return true;
    }

    /**
     * @brief Compares two tombstone objects.
     * @param other A tombstone object.
     * @return False in all cases.
     */
    [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const tombstone_t other) const noexcept {
        return false;
    }

    /**
     * @brief Compares a tombstone object and an identifier of any type.
     * @tparam Entity Type of identifier.
     * @param entity Identifier with which to compare.
     * @return False if the two elements differ, true otherwise.
     */
    template<typename Entity>
    [[nodiscard]] constexpr bool operator==(const Entity entity) const noexcept {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::to_version(entity) == entity_traits::to_version(*this);
    }

    /**
     * @brief Compares a tombstone object and an identifier of any type.
     * @tparam Entity Type of identifier.
     * @param entity Identifier with which to compare.
     * @return True if the two elements differ, false otherwise.
     */
    template<typename Entity>
    [[nodiscard]] constexpr bool operator!=(const Entity entity) const noexcept {
        return !(entity == *this);
    }
};

/**
 * @brief Compares a tombstone object and an identifier of any type.
 * @tparam Entity Type of identifier.
 * @param entity Identifier with which to compare.
 * @param other A tombstone object yet to be converted.
 * @return False if the two elements differ, true otherwise.
 */
template<typename Entity>
[[nodiscard]] constexpr bool operator==(const Entity entity, const tombstone_t other) noexcept {
    return other.operator==(entity);
}

/**
 * @brief Compares a tombstone object and an identifier of any type.
 * @tparam Entity Type of identifier.
 * @param entity Identifier with which to compare.
 * @param other A tombstone object yet to be converted.
 * @return True if the two elements differ, false otherwise.
 */
template<typename Entity>
[[nodiscard]] constexpr bool operator!=(const Entity entity, const tombstone_t other) noexcept {
    return !(other == entity);
}

/**
 * @brief Compile-time constant for null entities.
 *
 * There exist implicit conversions from this variable to identifiers of any
 * allowed type. Similarly, there exist comparison operators between the null
 * entity and any other identifier.
 */
inline constexpr null_t null{};

/**
 * @brief Compile-time constant for tombstone entities.
 *
 * There exist implicit conversions from this variable to identifiers of any
 * allowed type. Similarly, there exist comparison operators between the
 * tombstone entity and any other identifier.
 */
inline constexpr tombstone_t tombstone{};

} // namespace entt

#endif

// #include "entity/group.hpp"
#ifndef ENTT_ENTITY_GROUP_HPP
#define ENTT_ENTITY_GROUP_HPP

#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/type_traits.hpp"

// #include "component.hpp"
#ifndef ENTT_ENTITY_COMPONENT_HPP
#define ENTT_ENTITY_COMPONENT_HPP

#include <cstddef>
#include <type_traits>
// #include "../config/config.h"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, typename = void>
struct in_place_delete: std::bool_constant<!(std::is_move_constructible_v<Type> && std::is_move_assignable_v<Type>)> {};

template<typename Type>
struct in_place_delete<Type, std::enable_if_t<Type::in_place_delete>>
    : std::true_type {};

template<typename Type, typename = void>
struct page_size: std::integral_constant<std::size_t, !std::is_empty_v<ENTT_ETO_TYPE(Type)> * ENTT_PACKED_PAGE> {};

template<typename Type>
struct page_size<Type, std::enable_if_t<std::is_convertible_v<decltype(Type::page_size), std::size_t>>>
    : std::integral_constant<std::size_t, Type::page_size> {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Common way to access various properties of components.
 * @tparam Type Type of component.
 */
template<typename Type, typename = void>
struct component_traits {
    static_assert(std::is_same_v<std::decay_t<Type>, Type>, "Unsupported type");

    /*! @brief Component type. */
    using type = Type;

    /*! @brief Pointer stability, default is `false`. */
    static constexpr bool in_place_delete = internal::in_place_delete<Type>::value;
    /*! @brief Page size, default is `ENTT_PACKED_PAGE` for non-empty types. */
    static constexpr std::size_t page_size = internal::page_size<Type>::value;
};

/**
 * @brief Helper variable template.
 * @tparam Type Type of component.
 */
template<class Type>
inline constexpr bool ignore_as_empty_v = (std::is_void_v<Type> || component_traits<Type>::page_size == 0u);

} // namespace entt

#endif

// #include "entity.hpp"
#ifndef ENTT_ENTITY_ENTITY_HPP
#define ENTT_ENTITY_ENTITY_HPP

#include <cstddef>
#include <cstdint>
#include <type_traits>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct entt_traits;

template<typename Type>
struct entt_traits<Type, std::enable_if_t<std::is_enum_v<Type>>>
    : entt_traits<std::underlying_type_t<Type>> {};

template<typename Type>
struct entt_traits<Type, std::enable_if_t<std::is_class_v<Type>>>
    : entt_traits<typename Type::entity_type> {};

template<>
struct entt_traits<std::uint32_t> {
    using entity_type = std::uint32_t;
    using version_type = std::uint16_t;

    static constexpr entity_type entity_mask = 0xFFFFF;
    static constexpr entity_type version_mask = 0xFFF;
    static constexpr std::size_t entity_shift = 20u;
};

template<>
struct entt_traits<std::uint64_t> {
    using entity_type = std::uint64_t;
    using version_type = std::uint32_t;

    static constexpr entity_type entity_mask = 0xFFFFFFFF;
    static constexpr entity_type version_mask = 0xFFFFFFFF;
    static constexpr std::size_t entity_shift = 32u;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Entity traits.
 * @tparam Type Type of identifier.
 */
template<typename Type>
class entt_traits: internal::entt_traits<Type> {
    using base_type = internal::entt_traits<Type>;

public:
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Underlying entity type. */
    using entity_type = typename base_type::entity_type;
    /*! @brief Underlying version type. */
    using version_type = typename base_type::version_type;
    /*! @brief Reserved identifier. */
    static constexpr entity_type reserved = base_type::entity_mask | (base_type::version_mask << base_type::entity_shift);
    /*! @brief Page size, default is `ENTT_SPARSE_PAGE`. */
    static constexpr auto page_size = ENTT_SPARSE_PAGE;

    /**
     * @brief Converts an entity to its underlying type.
     * @param value The value to convert.
     * @return The integral representation of the given value.
     */
    [[nodiscard]] static constexpr entity_type to_integral(const value_type value) noexcept {
        return static_cast<entity_type>(value);
    }

    /**
     * @brief Returns the entity part once converted to the underlying type.
     * @param value The value to convert.
     * @return The integral representation of the entity part.
     */
    [[nodiscard]] static constexpr entity_type to_entity(const value_type value) noexcept {
        return (to_integral(value) & base_type::entity_mask);
    }

    /**
     * @brief Returns the version part once converted to the underlying type.
     * @param value The value to convert.
     * @return The integral representation of the version part.
     */
    [[nodiscard]] static constexpr version_type to_version(const value_type value) noexcept {
        return (to_integral(value) >> base_type::entity_shift);
    }

    /**
     * @brief Constructs an identifier from its parts.
     *
     * If the version part is not provided, a tombstone is returned.<br/>
     * If the entity part is not provided, a null identifier is returned.
     *
     * @param entity The entity part of the identifier.
     * @param version The version part of the identifier.
     * @return A properly constructed identifier.
     */
    [[nodiscard]] static constexpr value_type construct(const entity_type entity, const version_type version) noexcept {
        return value_type{(entity & base_type::entity_mask) | (static_cast<entity_type>(version) << base_type::entity_shift)};
    }

    /**
     * @brief Combines two identifiers in a single one.
     *
     * The returned identifier is a copy of the first element except for its
     * version, which is taken from the second element.
     *
     * @param lhs The identifier from which to take the entity part.
     * @param rhs The identifier from which to take the version part.
     * @return A properly constructed identifier.
     */
    [[nodiscard]] static constexpr value_type combine(const entity_type lhs, const entity_type rhs) noexcept {
        constexpr auto mask = (base_type::version_mask << base_type::entity_shift);
        return value_type{(lhs & base_type::entity_mask) | (rhs & mask)};
    }
};

/**
 * @copydoc entt_traits<Entity>::to_integral
 * @tparam Entity The value type.
 */
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::entity_type to_integral(const Entity value) noexcept {
    return entt_traits<Entity>::to_integral(value);
}

/**
 * @copydoc entt_traits<Entity>::to_entity
 * @tparam Entity The value type.
 */
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::entity_type to_entity(const Entity value) noexcept {
    return entt_traits<Entity>::to_entity(value);
}

/**
 * @copydoc entt_traits<Entity>::to_version
 * @tparam Entity The value type.
 */
template<typename Entity>
[[nodiscard]] constexpr typename entt_traits<Entity>::version_type to_version(const Entity value) noexcept {
    return entt_traits<Entity>::to_version(value);
}

/*! @brief Null object for all identifiers.  */
struct null_t {
    /**
     * @brief Converts the null object to identifiers of any type.
     * @tparam Entity Type of identifier.
     * @return The null representation for the given type.
     */
    template<typename Entity>
    [[nodiscard]] constexpr operator Entity() const noexcept {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::combine(entity_traits::reserved, entity_traits::reserved);
    }

    /**
     * @brief Compares two null objects.
     * @param other A null object.
     * @return True in all cases.
     */
    [[nodiscard]] constexpr bool operator==([[maybe_unused]] const null_t other) const noexcept {
        return true;
    }

    /**
     * @brief Compares two null objects.
     * @param other A null object.
     * @return False in all cases.
     */
    [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const null_t other) const noexcept {
        return false;
    }

    /**
     * @brief Compares a null object and an identifier of any type.
     * @tparam Entity Type of identifier.
     * @param entity Identifier with which to compare.
     * @return False if the two elements differ, true otherwise.
     */
    template<typename Entity>
    [[nodiscard]] constexpr bool operator==(const Entity entity) const noexcept {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::to_entity(entity) == entity_traits::to_entity(*this);
    }

    /**
     * @brief Compares a null object and an identifier of any type.
     * @tparam Entity Type of identifier.
     * @param entity Identifier with which to compare.
     * @return True if the two elements differ, false otherwise.
     */
    template<typename Entity>
    [[nodiscard]] constexpr bool operator!=(const Entity entity) const noexcept {
        return !(entity == *this);
    }
};

/**
 * @brief Compares a null object and an identifier of any type.
 * @tparam Entity Type of identifier.
 * @param entity Identifier with which to compare.
 * @param other A null object yet to be converted.
 * @return False if the two elements differ, true otherwise.
 */
template<typename Entity>
[[nodiscard]] constexpr bool operator==(const Entity entity, const null_t other) noexcept {
    return other.operator==(entity);
}

/**
 * @brief Compares a null object and an identifier of any type.
 * @tparam Entity Type of identifier.
 * @param entity Identifier with which to compare.
 * @param other A null object yet to be converted.
 * @return True if the two elements differ, false otherwise.
 */
template<typename Entity>
[[nodiscard]] constexpr bool operator!=(const Entity entity, const null_t other) noexcept {
    return !(other == entity);
}

/*! @brief Tombstone object for all identifiers.  */
struct tombstone_t {
    /**
     * @brief Converts the tombstone object to identifiers of any type.
     * @tparam Entity Type of identifier.
     * @return The tombstone representation for the given type.
     */
    template<typename Entity>
    [[nodiscard]] constexpr operator Entity() const noexcept {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::combine(entity_traits::reserved, entity_traits::reserved);
    }

    /**
     * @brief Compares two tombstone objects.
     * @param other A tombstone object.
     * @return True in all cases.
     */
    [[nodiscard]] constexpr bool operator==([[maybe_unused]] const tombstone_t other) const noexcept {
        return true;
    }

    /**
     * @brief Compares two tombstone objects.
     * @param other A tombstone object.
     * @return False in all cases.
     */
    [[nodiscard]] constexpr bool operator!=([[maybe_unused]] const tombstone_t other) const noexcept {
        return false;
    }

    /**
     * @brief Compares a tombstone object and an identifier of any type.
     * @tparam Entity Type of identifier.
     * @param entity Identifier with which to compare.
     * @return False if the two elements differ, true otherwise.
     */
    template<typename Entity>
    [[nodiscard]] constexpr bool operator==(const Entity entity) const noexcept {
        using entity_traits = entt_traits<Entity>;
        return entity_traits::to_version(entity) == entity_traits::to_version(*this);
    }

    /**
     * @brief Compares a tombstone object and an identifier of any type.
     * @tparam Entity Type of identifier.
     * @param entity Identifier with which to compare.
     * @return True if the two elements differ, false otherwise.
     */
    template<typename Entity>
    [[nodiscard]] constexpr bool operator!=(const Entity entity) const noexcept {
        return !(entity == *this);
    }
};

/**
 * @brief Compares a tombstone object and an identifier of any type.
 * @tparam Entity Type of identifier.
 * @param entity Identifier with which to compare.
 * @param other A tombstone object yet to be converted.
 * @return False if the two elements differ, true otherwise.
 */
template<typename Entity>
[[nodiscard]] constexpr bool operator==(const Entity entity, const tombstone_t other) noexcept {
    return other.operator==(entity);
}

/**
 * @brief Compares a tombstone object and an identifier of any type.
 * @tparam Entity Type of identifier.
 * @param entity Identifier with which to compare.
 * @param other A tombstone object yet to be converted.
 * @return True if the two elements differ, false otherwise.
 */
template<typename Entity>
[[nodiscard]] constexpr bool operator!=(const Entity entity, const tombstone_t other) noexcept {
    return !(other == entity);
}

/**
 * @brief Compile-time constant for null entities.
 *
 * There exist implicit conversions from this variable to identifiers of any
 * allowed type. Similarly, there exist comparison operators between the null
 * entity and any other identifier.
 */
inline constexpr null_t null{};

/**
 * @brief Compile-time constant for tombstone entities.
 *
 * There exist implicit conversions from this variable to identifiers of any
 * allowed type. Similarly, there exist comparison operators between the
 * tombstone entity and any other identifier.
 */
inline constexpr tombstone_t tombstone{};

} // namespace entt

#endif

// #include "fwd.hpp"

// #include "sparse_set.hpp"
#ifndef ENTT_ENTITY_SPARSE_SET_HPP
#define ENTT_ENTITY_SPARSE_SET_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/algorithm.hpp"
#ifndef ENTT_CORE_ALGORITHM_HPP
#define ENTT_CORE_ALGORITHM_HPP

#include <algorithm>
#include <functional>
#include <iterator>
#include <utility>
#include <vector>
// #include "utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif


namespace entt {

/**
 * @brief Function object to wrap `std::sort` in a class type.
 *
 * Unfortunately, `std::sort` cannot be passed as template argument to a class
 * template or a function template.<br/>
 * This class fills the gap by wrapping some flavors of `std::sort` in a
 * function object.
 */
struct std_sort {
    /**
     * @brief Sorts the elements in a range.
     *
     * Sorts the elements in a range using the given binary comparison function.
     *
     * @tparam It Type of random access iterator.
     * @tparam Compare Type of comparison function object.
     * @tparam Args Types of arguments to forward to the sort function.
     * @param first An iterator to the first element of the range to sort.
     * @param last An iterator past the last element of the range to sort.
     * @param compare A valid comparison function object.
     * @param args Arguments to forward to the sort function, if any.
     */
    template<typename It, typename Compare = std::less<>, typename... Args>
    void operator()(It first, It last, Compare compare = Compare{}, Args &&...args) const {
        std::sort(std::forward<Args>(args)..., std::move(first), std::move(last), std::move(compare));
    }
};

/*! @brief Function object for performing insertion sort. */
struct insertion_sort {
    /**
     * @brief Sorts the elements in a range.
     *
     * Sorts the elements in a range using the given binary comparison function.
     *
     * @tparam It Type of random access iterator.
     * @tparam Compare Type of comparison function object.
     * @param first An iterator to the first element of the range to sort.
     * @param last An iterator past the last element of the range to sort.
     * @param compare A valid comparison function object.
     */
    template<typename It, typename Compare = std::less<>>
    void operator()(It first, It last, Compare compare = Compare{}) const {
        if(first < last) {
            for(auto it = first + 1; it < last; ++it) {
                auto value = std::move(*it);
                auto pre = it;

                for(; pre > first && compare(value, *(pre - 1)); --pre) {
                    *pre = std::move(*(pre - 1));
                }

                *pre = std::move(value);
            }
        }
    }
};

/**
 * @brief Function object for performing LSD radix sort.
 * @tparam Bit Number of bits processed per pass.
 * @tparam N Maximum number of bits to sort.
 */
template<std::size_t Bit, std::size_t N>
struct radix_sort {
    static_assert((N % Bit) == 0, "The maximum number of bits to sort must be a multiple of the number of bits processed per pass");

    /**
     * @brief Sorts the elements in a range.
     *
     * Sorts the elements in a range using the given _getter_ to access the
     * actual data to be sorted.
     *
     * This implementation is inspired by the online book
     * [Physically Based Rendering](http://www.pbr-book.org/3ed-2018/Primitives_and_Intersection_Acceleration/Bounding_Volume_Hierarchies.html#RadixSort).
     *
     * @tparam It Type of random access iterator.
     * @tparam Getter Type of _getter_ function object.
     * @param first An iterator to the first element of the range to sort.
     * @param last An iterator past the last element of the range to sort.
     * @param getter A valid _getter_ function object.
     */
    template<typename It, typename Getter = identity>
    void operator()(It first, It last, Getter getter = Getter{}) const {
        if(first < last) {
            static constexpr auto mask = (1 << Bit) - 1;
            static constexpr auto buckets = 1 << Bit;
            static constexpr auto passes = N / Bit;

            using value_type = typename std::iterator_traits<It>::value_type;
            std::vector<value_type> aux(std::distance(first, last));

            auto part = [getter = std::move(getter)](auto from, auto to, auto out, auto start) {
                std::size_t index[buckets]{};
                std::size_t count[buckets]{};

                for(auto it = from; it != to; ++it) {
                    ++count[(getter(*it) >> start) & mask];
                }

                for(std::size_t pos{}, end = buckets - 1u; pos < end; ++pos) {
                    index[pos + 1u] = index[pos] + count[pos];
                }

                for(auto it = from; it != to; ++it) {
                    out[index[(getter(*it) >> start) & mask]++] = std::move(*it);
                }
            };

            for(std::size_t pass = 0; pass < (passes & ~1); pass += 2) {
                part(first, last, aux.begin(), pass * Bit);
                part(aux.begin(), aux.end(), first, (pass + 1) * Bit);
            }

            if constexpr(passes & 1) {
                part(first, last, aux.begin(), (passes - 1) * Bit);
                std::move(aux.begin(), aux.end(), first);
            }
        }
    }
};

} // namespace entt

#endif

// #include "../core/any.hpp"
#ifndef ENTT_CORE_ANY_HPP
#define ENTT_CORE_ANY_HPP

#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "fwd.hpp"

// #include "type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"
#ifndef ENTT_CORE_ATTRIBUTE_H
#define ENTT_CORE_ATTRIBUTE_H

#ifndef ENTT_EXPORT
#    if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
#        define ENTT_EXPORT __declspec(dllexport)
#        define ENTT_IMPORT __declspec(dllimport)
#        define ENTT_HIDDEN
#    elif defined __GNUC__ && __GNUC__ >= 4
#        define ENTT_EXPORT __attribute__((visibility("default")))
#        define ENTT_IMPORT __attribute__((visibility("default")))
#        define ENTT_HIDDEN __attribute__((visibility("hidden")))
#    else /* Unsupported compiler */
#        define ENTT_EXPORT
#        define ENTT_IMPORT
#        define ENTT_HIDDEN
#    endif
#endif

#ifndef ENTT_API
#    if defined ENTT_API_EXPORT
#        define ENTT_API ENTT_EXPORT
#    elif defined ENTT_API_IMPORT
#        define ENTT_API ENTT_IMPORT
#    else /* No API */
#        define ENTT_API
#    endif
#endif

#endif

// #include "fwd.hpp"

// #include "hashed_string.hpp"
#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP

#include <cstddef>
#include <cstdint>
// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename>
struct fnv1a_traits;

template<>
struct fnv1a_traits<std::uint32_t> {
    using type = std::uint32_t;
    static constexpr std::uint32_t offset = 2166136261;
    static constexpr std::uint32_t prime = 16777619;
};

template<>
struct fnv1a_traits<std::uint64_t> {
    using type = std::uint64_t;
    static constexpr std::uint64_t offset = 14695981039346656037ull;
    static constexpr std::uint64_t prime = 1099511628211ull;
};

template<typename Char>
struct basic_hashed_string {
    using value_type = Char;
    using size_type = std::size_t;
    using hash_type = id_type;

    const value_type *repr;
    size_type length;
    hash_type hash;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Zero overhead unique identifier.
 *
 * A hashed string is a compile-time tool that allows users to use
 * human-readable identifiers in the codebase while using their numeric
 * counterparts at runtime.<br/>
 * Because of that, a hashed string can also be used in constant expressions if
 * required.
 *
 * @warning
 * This class doesn't take ownership of user-supplied strings nor does it make a
 * copy of them.
 *
 * @tparam Char Character type.
 */
template<typename Char>
class basic_hashed_string: internal::basic_hashed_string<Char> {
    using base_type = internal::basic_hashed_string<Char>;
    using hs_traits = internal::fnv1a_traits<id_type>;

    struct const_wrapper {
        // non-explicit constructor on purpose
        constexpr const_wrapper(const Char *str) noexcept
            : repr{str} {}

        const Char *repr;
    };

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str) noexcept {
        base_type base{str, 0u, hs_traits::offset};

        for(; str[base.length]; ++base.length) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[base.length])) * hs_traits::prime;
        }

        return base;
    }

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str, const std::size_t len) noexcept {
        base_type base{str, len, hs_traits::offset};

        for(size_type pos{}; pos < len; ++pos) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[pos])) * hs_traits::prime;
        }

        return base;
    }

public:
    /*! @brief Character type. */
    using value_type = typename base_type::value_type;
    /*! @brief Unsigned integer type. */
    using size_type = typename base_type::size_type;
    /*! @brief Unsigned integer type. */
    using hash_type = typename base_type::hash_type;

    /**
     * @brief Returns directly the numeric representation of a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const value_type *str, const size_type len) noexcept {
        return basic_hashed_string{str, len};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     * @return The numeric representation of the string.
     */
    template<std::size_t N>
    [[nodiscard]] static constexpr hash_type value(const value_type (&str)[N]) noexcept {
        return basic_hashed_string{str};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @param wrapper Helps achieving the purpose by relying on overloading.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const_wrapper wrapper) noexcept {
        return basic_hashed_string{wrapper};
    }

    /*! @brief Constructs an empty hashed string. */
    constexpr basic_hashed_string() noexcept
        : base_type{} {}

    /**
     * @brief Constructs a hashed string from a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     */
    constexpr basic_hashed_string(const value_type *str, const size_type len) noexcept
        : base_type{helper(str, len)} {}

    /**
     * @brief Constructs a hashed string from an array of const characters.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     */
    template<std::size_t N>
    constexpr basic_hashed_string(const value_type (&str)[N]) noexcept
        : base_type{helper(str)} {}

    /**
     * @brief Explicit constructor on purpose to avoid constructing a hashed
     * string directly from a `const value_type *`.
     *
     * @warning
     * The lifetime of the string is not extended nor is it copied.
     *
     * @param wrapper Helps achieving the purpose by relying on overloading.
     */
    explicit constexpr basic_hashed_string(const_wrapper wrapper) noexcept
        : base_type{helper(wrapper.repr)} {}

    /**
     * @brief Returns the size a hashed string.
     * @return The size of the hashed string.
     */
    [[nodiscard]] constexpr size_type size() const noexcept {
        return base_type::length;
    }

    /**
     * @brief Returns the human-readable representation of a hashed string.
     * @return The string used to initialize the hashed string.
     */
    [[nodiscard]] constexpr const value_type *data() const noexcept {
        return base_type::repr;
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr hash_type value() const noexcept {
        return base_type::hash;
    }

    /*! @copydoc data */
    [[nodiscard]] constexpr operator const value_type *() const noexcept {
        return data();
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr operator hash_type() const noexcept {
        return value();
    }
};

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @param str Human-readable identifier.
 * @param len Length of the string to hash.
 */
template<typename Char>
basic_hashed_string(const Char *str, const std::size_t len) -> basic_hashed_string<Char>;

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @tparam N Number of characters of the identifier.
 * @param str Human-readable identifier.
 */
template<typename Char, std::size_t N>
basic_hashed_string(const Char (&str)[N]) -> basic_hashed_string<Char>;

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings are identical, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator==(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() == rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings differ, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than the second, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() < rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs < rhs);
}

/*! @brief Aliases for common character types. */
using hashed_string = basic_hashed_string<char>;

/*! @brief Aliases for common character types. */
using hashed_wstring = basic_hashed_string<wchar_t>;

inline namespace literals {

/**
 * @brief User defined literal for hashed strings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed string.
 */
[[nodiscard]] constexpr hashed_string operator"" _hs(const char *str, std::size_t) noexcept {
    return hashed_string{str};
}

/**
 * @brief User defined literal for hashed wstrings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed wstring.
 */
[[nodiscard]] constexpr hashed_wstring operator"" _hws(const wchar_t *str, std::size_t) noexcept {
    return hashed_wstring{str};
}

} // namespace literals

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

enum class any_operation : std::uint8_t {
    copy,
    move,
    transfer,
    assign,
    destroy,
    compare,
    get
};

enum class any_policy : std::uint8_t {
    owner,
    ref,
    cref
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A SBO friendly, type-safe container for single values of any type.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 */
template<std::size_t Len, std::size_t Align>
class basic_any {
    using operation = internal::any_operation;
    using policy = internal::any_policy;
    using vtable_type = const void *(const operation, const basic_any &, const void *);

    struct storage_type {
        alignas(Align) std::byte data[Len + !Len];
    };

    template<typename Type>
    static constexpr bool in_situ = Len && alignof(Type) <= Align && sizeof(Type) <= Len &&std::is_nothrow_move_constructible_v<Type>;

    template<typename Type>
    static const void *basic_vtable(const operation op, const basic_any &value, const void *other) {
        static_assert(!std::is_same_v<Type, void> && std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, Type>, "Invalid type");
        const Type *element = nullptr;

        if constexpr(in_situ<Type>) {
            element = value.owner() ? reinterpret_cast<const Type *>(&value.storage) : static_cast<const Type *>(value.instance);
        } else {
            element = static_cast<const Type *>(value.instance);
        }

        switch(op) {
        case operation::copy:
            if constexpr(std::is_copy_constructible_v<Type>) {
                static_cast<basic_any *>(const_cast<void *>(other))->initialize<Type>(*element);
            }
            break;
        case operation::move:
            if constexpr(in_situ<Type>) {
                if(value.owner()) {
                    return new(&static_cast<basic_any *>(const_cast<void *>(other))->storage) Type{std::move(*const_cast<Type *>(element))};
                }
            }

            return (static_cast<basic_any *>(const_cast<void *>(other))->instance = std::exchange(const_cast<basic_any &>(value).instance, nullptr));
        case operation::transfer:
            if constexpr(std::is_move_assignable_v<Type>) {
                *const_cast<Type *>(element) = std::move(*static_cast<Type *>(const_cast<void *>(other)));
                return other;
            }
            [[fallthrough]];
        case operation::assign:
            if constexpr(std::is_copy_assignable_v<Type>) {
                *const_cast<Type *>(element) = *static_cast<const Type *>(other);
                return other;
            }
            break;
        case operation::destroy:
            if constexpr(in_situ<Type>) {
                element->~Type();
            } else if constexpr(std::is_array_v<Type>) {
                delete[] element;
            } else {
                delete element;
            }
            break;
        case operation::compare:
            if constexpr(!std::is_function_v<Type> && !std::is_array_v<Type> && is_equality_comparable_v<Type>) {
                return *element == *static_cast<const Type *>(other) ? other : nullptr;
            } else {
                return (element == other) ? other : nullptr;
            }
        case operation::get:
            return element;
        }

        return nullptr;
    }

    template<typename Type, typename... Args>
    void initialize([[maybe_unused]] Args &&...args) {
        info = &type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();

        if constexpr(!std::is_void_v<Type>) {
            vtable = basic_vtable<std::remove_cv_t<std::remove_reference_t<Type>>>;

            if constexpr(std::is_lvalue_reference_v<Type>) {
                static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
                mode = std::is_const_v<std::remove_reference_t<Type>> ? policy::cref : policy::ref;
                instance = (std::addressof(args), ...);
            } else if constexpr(in_situ<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                if constexpr(sizeof...(Args) != 0u && std::is_aggregate_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                    new(&storage) std::remove_cv_t<std::remove_reference_t<Type>>{std::forward<Args>(args)...};
                } else {
                    new(&storage) std::remove_cv_t<std::remove_reference_t<Type>>(std::forward<Args>(args)...);
                }
            } else {
                if constexpr(sizeof...(Args) != 0u && std::is_aggregate_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                    instance = new std::remove_cv_t<std::remove_reference_t<Type>>{std::forward<Args>(args)...};
                } else {
                    instance = new std::remove_cv_t<std::remove_reference_t<Type>>(std::forward<Args>(args)...);
                }
            }
        }
    }

    basic_any(const basic_any &other, const policy pol) noexcept
        : instance{other.data()},
          info{other.info},
          vtable{other.vtable},
          mode{pol} {}

public:
    /*! @brief Size of the internal storage. */
    static constexpr auto length = Len;
    /*! @brief Alignment requirement. */
    static constexpr auto alignment = Align;

    /*! @brief Default constructor. */
    constexpr basic_any() noexcept
        : basic_any{std::in_place_type<void>} {}

    /**
     * @brief Constructs a wrapper by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit basic_any(std::in_place_type_t<Type>, Args &&...args)
        : instance{},
          info{},
          vtable{},
          mode{policy::owner} {
        initialize<Type>(std::forward<Args>(args)...);
    }

    /**
     * @brief Constructs a wrapper from a given value.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
    basic_any(Type &&value)
        : basic_any{std::in_place_type<std::decay_t<Type>>, std::forward<Type>(value)} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    basic_any(const basic_any &other)
        : basic_any{} {
        if(other.vtable) {
            other.vtable(operation::copy, other, this);
        }
    }

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_any(basic_any &&other) noexcept
        : instance{},
          info{other.info},
          vtable{other.vtable},
          mode{other.mode} {
        if(other.vtable) {
            other.vtable(operation::move, other, this);
        }
    }

    /*! @brief Frees the internal storage, whatever it means. */
    ~basic_any() {
        if(vtable && owner()) {
            vtable(operation::destroy, *this, nullptr);
        }
    }

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This any object.
     */
    basic_any &operator=(const basic_any &other) {
        reset();

        if(other.vtable) {
            other.vtable(operation::copy, other, this);
        }

        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This any object.
     */
    basic_any &operator=(basic_any &&other) noexcept {
        reset();

        if(other.vtable) {
            other.vtable(operation::move, other, this);
            info = other.info;
            vtable = other.vtable;
            mode = other.mode;
        }

        return *this;
    }

    /**
     * @brief Value assignment operator.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     * @return This any object.
     */
    template<typename Type>
    std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any &>
    operator=(Type &&value) {
        emplace<std::decay_t<Type>>(std::forward<Type>(value));
        return *this;
    }

    /**
     * @brief Returns the object type if any, `type_id<void>()` otherwise.
     * @return The object type if any, `type_id<void>()` otherwise.
     */
    [[nodiscard]] const type_info &type() const noexcept {
        return *info;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data() const noexcept {
        return vtable ? vtable(operation::get, *this, nullptr) : nullptr;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @param req Expected type.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data(const type_info &req) const noexcept {
        return *info == req ? data() : nullptr;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] void *data() noexcept {
        return mode == policy::cref ? nullptr : const_cast<void *>(std::as_const(*this).data());
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @param req Expected type.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] void *data(const type_info &req) noexcept {
        return mode == policy::cref ? nullptr : const_cast<void *>(std::as_const(*this).data(req));
    }

    /**
     * @brief Replaces the contained object by creating a new instance directly.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    void emplace(Args &&...args) {
        reset();
        initialize<Type>(std::forward<Args>(args)...);
    }

    /**
     * @brief Assigns a value to the contained object without replacing it.
     * @param other The value to assign to the contained object.
     * @return True in case of success, false otherwise.
     */
    bool assign(const basic_any &other) {
        if(vtable && mode != policy::cref && *info == *other.info) {
            return (vtable(operation::assign, *this, other.data()) != nullptr);
        }

        return false;
    }

    /*! @copydoc assign */
    bool assign(basic_any &&other) {
        if(vtable && mode != policy::cref && *info == *other.info) {
            if(auto *val = other.data(); val) {
                return (vtable(operation::transfer, *this, val) != nullptr);
            } else {
                return (vtable(operation::assign, *this, std::as_const(other).data()) != nullptr);
            }
        }

        return false;
    }

    /*! @brief Destroys contained object */
    void reset() {
        if(vtable && owner()) {
            vtable(operation::destroy, *this, nullptr);
        }

        // unnecessary but it helps to detect nasty bugs
        ENTT_ASSERT((instance = nullptr) == nullptr, "");
        info = &type_id<void>();
        vtable = nullptr;
        mode = policy::owner;
    }

    /**
     * @brief Returns false if a wrapper is empty, true otherwise.
     * @return False if the wrapper is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return vtable != nullptr;
    }

    /**
     * @brief Checks if two wrappers differ in their content.
     * @param other Wrapper with which to compare.
     * @return False if the two objects differ in their content, true otherwise.
     */
    [[nodiscard]] bool operator==(const basic_any &other) const noexcept {
        if(vtable && *info == *other.info) {
            return (vtable(operation::compare, *this, other.data()) != nullptr);
        }

        return (!vtable && !other.vtable);
    }

    /**
     * @brief Checks if two wrappers differ in their content.
     * @param other Wrapper with which to compare.
     * @return True if the two objects differ in their content, false otherwise.
     */
    [[nodiscard]] bool operator!=(const basic_any &other) const noexcept {
        return !(*this == other);
    }

    /**
     * @brief Aliasing constructor.
     * @return A wrapper that shares a reference to an unmanaged object.
     */
    [[nodiscard]] basic_any as_ref() noexcept {
        return basic_any{*this, (mode == policy::cref ? policy::cref : policy::ref)};
    }

    /*! @copydoc as_ref */
    [[nodiscard]] basic_any as_ref() const noexcept {
        return basic_any{*this, policy::cref};
    }

    /**
     * @brief Returns true if a wrapper owns its object, false otherwise.
     * @return True if the wrapper owns its object, false otherwise.
     */
    [[nodiscard]] bool owner() const noexcept {
        return (mode == policy::owner);
    }

private:
    union {
        const void *instance;
        storage_type storage;
    };
    const type_info *info;
    vtable_type *vtable;
    policy mode;
};

/**
 * @brief Performs type-safe access to the contained object.
 * @tparam Type Type to which conversion is required.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Alignment requirement.
 * @param data Target any object.
 * @return The element converted to the requested type.
 */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(const basic_any<Len, Align> &data) noexcept {
    const auto *const instance = any_cast<std::remove_reference_t<Type>>(&data);
    ENTT_ASSERT(instance, "Invalid instance");
    return static_cast<Type>(*instance);
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(basic_any<Len, Align> &data) noexcept {
    // forces const on non-reference types to make them work also with wrappers for const references
    auto *const instance = any_cast<std::remove_reference_t<const Type>>(&data);
    ENTT_ASSERT(instance, "Invalid instance");
    return static_cast<Type>(*instance);
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(basic_any<Len, Align> &&data) noexcept {
    if constexpr(std::is_copy_constructible_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
        if(auto *const instance = any_cast<std::remove_reference_t<Type>>(&data); instance) {
            return static_cast<Type>(std::move(*instance));
        } else {
            return any_cast<Type>(data);
        }
    } else {
        auto *const instance = any_cast<std::remove_reference_t<Type>>(&data);
        ENTT_ASSERT(instance, "Invalid instance");
        return static_cast<Type>(std::move(*instance));
    }
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
const Type *any_cast(const basic_any<Len, Align> *data) noexcept {
    const auto &info = type_id<std::remove_cv_t<Type>>();
    return static_cast<const Type *>(data->data(info));
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type *any_cast(basic_any<Len, Align> *data) noexcept {
    if constexpr(std::is_const_v<Type>) {
        // last attempt to make wrappers for const references return their values
        return any_cast<Type>(&std::as_const(*data));
    } else {
        const auto &info = type_id<std::remove_cv_t<Type>>();
        return static_cast<Type *>(data->data(info));
    }
}

/**
 * @brief Constructs a wrapper from a given type, passing it all arguments.
 * @tparam Type Type of object to use to initialize the wrapper.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 * @tparam Args Types of arguments to use to construct the new instance.
 * @param args Parameters to use to construct the instance.
 * @return A properly initialized wrapper for an object of the given type.
 */
template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
basic_any<Len, Align> make_any(Args &&...args) {
    return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
}

/**
 * @brief Forwards its argument and avoids copies for lvalue references.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 * @tparam Type Type of argument to use to construct the new instance.
 * @param value Parameter to use to construct the instance.
 * @return A properly initialized and not necessarily owning wrapper.
 */
template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
basic_any<Len, Align> forward_as_any(Type &&value) {
    return basic_any<Len, Align>{std::in_place_type<Type &&>, std::forward<Type>(value)};
}

} // namespace entt

#endif

// #include "../core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "../core/type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"

// #include "fwd.hpp"

// #include "hashed_string.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "entity.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Container>
struct sparse_set_iterator final {
    using value_type = typename Container::value_type;
    using pointer = typename Container::const_pointer;
    using reference = typename Container::const_reference;
    using difference_type = typename Container::difference_type;
    using iterator_category = std::random_access_iterator_tag;

    constexpr sparse_set_iterator() noexcept
        : packed{},
          offset{} {}

    constexpr sparse_set_iterator(const Container &ref, const difference_type idx) noexcept
        : packed{std::addressof(ref)},
          offset{idx} {}

    constexpr sparse_set_iterator &operator++() noexcept {
        return --offset, *this;
    }

    constexpr sparse_set_iterator operator++(int) noexcept {
        sparse_set_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr sparse_set_iterator &operator--() noexcept {
        return ++offset, *this;
    }

    constexpr sparse_set_iterator operator--(int) noexcept {
        sparse_set_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr sparse_set_iterator &operator+=(const difference_type value) noexcept {
        offset -= value;
        return *this;
    }

    constexpr sparse_set_iterator operator+(const difference_type value) const noexcept {
        sparse_set_iterator copy = *this;
        return (copy += value);
    }

    constexpr sparse_set_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr sparse_set_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return packed->data()[index() - value];
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return packed->data() + index();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr difference_type index() const noexcept {
        return offset - 1;
    }

private:
    const Container *packed;
    difference_type offset;
};

template<typename Type, typename Other>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return rhs.index() - lhs.index();
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator==(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator!=(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator<(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return lhs.index() > rhs.index();
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator>(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return lhs.index() < rhs.index();
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator<=(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator>=(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return !(lhs < rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @brief Sparse set deletion policy. */
enum class deletion_policy : std::uint8_t {
    /*! @brief Swap-and-pop deletion policy. */
    swap_and_pop = 0u,
    /*! @brief In-place deletion policy. */
    in_place = 1u
};

/**
 * @brief Basic sparse set implementation.
 *
 * Sparse set or packed array or whatever is the name users give it.<br/>
 * Two arrays: an _external_ one and an _internal_ one; a _sparse_ one and a
 * _packed_ one; one used for direct access through contiguous memory, the other
 * one used to get the data through an extra level of indirection.<br/>
 * This is largely used by the registry to offer users the fastest access ever
 * to the components. Views and groups in general are almost entirely designed
 * around sparse sets.
 *
 * This type of data structure is widely documented in the literature and on the
 * web. This is nothing more than a customized implementation suitable for the
 * purpose of the framework.
 *
 * @note
 * Internal data structures arrange elements to maximize performance. There are
 * no guarantees that entities are returned in the insertion order when iterate
 * a sparse set. Do not make assumption on the order in any case.
 *
 * @tparam Entity A valid entity type (see entt_traits for more details).
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Entity, typename Allocator>
class basic_sparse_set {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Entity>, "Invalid value type");
    using sparse_container_type = std::vector<typename alloc_traits::pointer, typename alloc_traits::template rebind_alloc<typename alloc_traits::pointer>>;
    using packed_container_type = std::vector<Entity, Allocator>;
    using entity_traits = entt_traits<Entity>;

    [[nodiscard]] auto sparse_ptr(const Entity entt) const {
        const auto pos = static_cast<size_type>(entity_traits::to_entity(entt));
        const auto page = pos / entity_traits::page_size;
        return (page < sparse.size() && sparse[page]) ? (sparse[page] + fast_mod(pos, entity_traits::page_size)) : nullptr;
    }

    [[nodiscard]] auto &sparse_ref(const Entity entt) const {
        ENTT_ASSERT(sparse_ptr(entt), "Invalid element");
        const auto pos = static_cast<size_type>(entity_traits::to_entity(entt));
        return sparse[pos / entity_traits::page_size][fast_mod(pos, entity_traits::page_size)];
    }

    [[nodiscard]] auto &assure_at_least(const Entity entt) {
        const auto pos = static_cast<size_type>(entity_traits::to_entity(entt));
        const auto page = pos / entity_traits::page_size;

        if(!(page < sparse.size())) {
            sparse.resize(page + 1u, nullptr);
        }

        if(!sparse[page]) {
            auto page_allocator{packed.get_allocator()};
            sparse[page] = alloc_traits::allocate(page_allocator, entity_traits::page_size);
            std::uninitialized_fill(sparse[page], sparse[page] + entity_traits::page_size, null);
        }

        auto &elem = sparse[page][fast_mod(pos, entity_traits::page_size)];
        ENTT_ASSERT(elem == null, "Slot not available");
        return elem;
    }

    void release_sparse_pages() {
        auto page_allocator{packed.get_allocator()};

        for(auto &&page: sparse) {
            if(page != nullptr) {
                std::destroy(page, page + entity_traits::page_size);
                alloc_traits::deallocate(page_allocator, page, entity_traits::page_size);
                page = nullptr;
            }
        }
    }

private:
    virtual const void *get_at(const std::size_t) const {
        return nullptr;
    }

    virtual void swap_at(const std::size_t, const std::size_t) {}
    virtual void move_element(const std::size_t, const std::size_t) {}

protected:
    /*! @brief Random access iterator type. */
    using basic_iterator = internal::sparse_set_iterator<packed_container_type>;

    /**
     * @brief Erases an entity from a sparse set.
     * @param it An iterator to the element to pop.
     */
    void swap_and_pop(const basic_iterator it) {
        ENTT_ASSERT(mode == deletion_policy::swap_and_pop, "Deletion policy mismatched");
        auto &self = sparse_ref(*it);
        const auto entt = entity_traits::to_entity(self);
        sparse_ref(packed.back()) = entity_traits::combine(entt, entity_traits::to_integral(packed.back()));
        packed[static_cast<size_type>(entt)] = packed.back();
        // unnecessary but it helps to detect nasty bugs
        ENTT_ASSERT((packed.back() = null, true), "");
        // lazy self-assignment guard
        self = null;
        packed.pop_back();
    }

    /**
     * @brief Erases an entity from a sparse set.
     * @param it An iterator to the element to pop.
     */
    void in_place_pop(const basic_iterator it) {
        ENTT_ASSERT(mode == deletion_policy::in_place, "Deletion policy mismatched");
        const auto entt = entity_traits::to_entity(std::exchange(sparse_ref(*it), null));
        packed[static_cast<size_type>(entt)] = std::exchange(free_list, entity_traits::combine(entt, entity_traits::reserved));
    }

protected:
    /**
     * @brief Erases entities from a sparse set.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    virtual void pop(basic_iterator first, basic_iterator last) {
        if(mode == deletion_policy::swap_and_pop) {
            for(; first != last; ++first) {
                swap_and_pop(first);
            }
        } else {
            for(; first != last; ++first) {
                in_place_pop(first);
            }
        }
    }

    /**
     * @brief Assigns an entity to a sparse set.
     * @param entt A valid identifier.
     * @param force_back Force back insertion.
     * @return Iterator pointing to the emplaced element.
     */
    virtual basic_iterator try_emplace(const Entity entt, const bool force_back, const void * = nullptr) {
        ENTT_ASSERT(!contains(entt), "Set already contains entity");

        if(auto &elem = assure_at_least(entt); free_list == null || force_back) {
            packed.push_back(entt);
            elem = entity_traits::combine(static_cast<typename entity_traits::entity_type>(packed.size() - 1u), entity_traits::to_integral(entt));
            return begin();
        } else {
            const auto pos = static_cast<size_type>(entity_traits::to_entity(free_list));
            elem = entity_traits::combine(entity_traits::to_integral(free_list), entity_traits::to_integral(entt));
            free_list = std::exchange(packed[pos], entt);
            return --(end() - pos);
        }
    }

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename entity_traits::value_type;
    /*! @brief Underlying version type. */
    using version_type = typename entity_traits::version_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Pointer type to contained entities. */
    using pointer = typename packed_container_type::const_pointer;
    /*! @brief Random access iterator type. */
    using iterator = basic_iterator;
    /*! @brief Constant random access iterator type. */
    using const_iterator = iterator;
    /*! @brief Reverse iterator type. */
    using reverse_iterator = std::reverse_iterator<iterator>;
    /*! @brief Constant reverse iterator type. */
    using const_reverse_iterator = reverse_iterator;

    /*! @brief Default constructor. */
    basic_sparse_set()
        : basic_sparse_set{type_id<void>()} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_sparse_set(const allocator_type &allocator)
        : basic_sparse_set{type_id<void>(), deletion_policy::swap_and_pop, allocator} {}

    /**
     * @brief Constructs an empty container with the given policy and allocator.
     * @param pol Type of deletion policy.
     * @param allocator The allocator to use (possibly default-constructed).
     */
    explicit basic_sparse_set(deletion_policy pol, const allocator_type &allocator = {})
        : basic_sparse_set{type_id<void>(), pol, allocator} {}

    /**
     * @brief Constructs an empty container with the given value type, policy
     * and allocator.
     * @param value Returned value type, if any.
     * @param pol Type of deletion policy.
     * @param allocator The allocator to use (possibly default-constructed).
     */
    explicit basic_sparse_set(const type_info &value, deletion_policy pol = deletion_policy::swap_and_pop, const allocator_type &allocator = {})
        : sparse{allocator},
          packed{allocator},
          info{&value},
          free_list{tombstone},
          mode{pol} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_sparse_set(basic_sparse_set &&other) noexcept
        : sparse{std::move(other.sparse)},
          packed{std::move(other.packed)},
          info{other.info},
          free_list{std::exchange(other.free_list, tombstone)},
          mode{other.mode} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_sparse_set(basic_sparse_set &&other, const allocator_type &allocator) noexcept
        : sparse{std::move(other.sparse), allocator},
          packed{std::move(other.packed), allocator},
          info{other.info},
          free_list{std::exchange(other.free_list, tombstone)},
          mode{other.mode} {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || packed.get_allocator() == other.packed.get_allocator(), "Copying a sparse set is not allowed");
    }

    /*! @brief Default destructor. */
    virtual ~basic_sparse_set() {
        release_sparse_pages();
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This sparse set.
     */
    basic_sparse_set &operator=(basic_sparse_set &&other) noexcept {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || packed.get_allocator() == other.packed.get_allocator(), "Copying a sparse set is not allowed");

        release_sparse_pages();
        sparse = std::move(other.sparse);
        packed = std::move(other.packed);
        info = other.info;
        free_list = std::exchange(other.free_list, tombstone);
        mode = other.mode;
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given sparse set.
     * @param other Sparse set to exchange the content with.
     */
    void swap(basic_sparse_set &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(info, other.info);
        swap(free_list, other.free_list);
        swap(mode, other.mode);
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return packed.get_allocator();
    }

    /**
     * @brief Returns the deletion policy of a sparse set.
     * @return The deletion policy of the sparse set.
     */
    [[nodiscard]] deletion_policy policy() const noexcept {
        return mode;
    }

    /**
     * @brief Increases the capacity of a sparse set.
     *
     * If the new capacity is greater than the current capacity, new storage is
     * allocated, otherwise the method does nothing.
     *
     * @param cap Desired capacity.
     */
    virtual void reserve(const size_type cap) {
        packed.reserve(cap);
    }

    /**
     * @brief Returns the number of elements that a sparse set has currently
     * allocated space for.
     * @return Capacity of the sparse set.
     */
    [[nodiscard]] virtual size_type capacity() const noexcept {
        return packed.capacity();
    }

    /*! @brief Requests the removal of unused capacity. */
    virtual void shrink_to_fit() {
        packed.shrink_to_fit();
    }

    /**
     * @brief Returns the extent of a sparse set.
     *
     * The extent of a sparse set is also the size of the internal sparse array.
     * There is no guarantee that the internal packed array has the same size.
     * Usually the size of the internal sparse array is equal or greater than
     * the one of the internal packed array.
     *
     * @return Extent of the sparse set.
     */
    [[nodiscard]] size_type extent() const noexcept {
        return sparse.size() * entity_traits::page_size;
    }

    /**
     * @brief Returns the number of elements in a sparse set.
     *
     * The number of elements is also the size of the internal packed array.
     * There is no guarantee that the internal sparse array has the same size.
     * Usually the size of the internal sparse array is equal or greater than
     * the one of the internal packed array.
     *
     * @return Number of elements.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.size();
    }

    /**
     * @brief Checks whether a sparse set is empty.
     * @return True if the sparse set is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.empty();
    }

    /**
     * @brief Direct access to the internal packed array.
     * @return A pointer to the internal packed array.
     */
    [[nodiscard]] pointer data() const noexcept {
        return packed.data();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first entity of the internal packed
     * array. If the sparse set is empty, the returned iterator will be equal to
     * `end()`.
     *
     * @return An iterator to the first entity of the sparse set.
     */
    [[nodiscard]] const_iterator begin() const noexcept {
        const auto pos = static_cast<typename iterator::difference_type>(packed.size());
        return iterator{packed, pos};
    }

    /*! @copydoc begin */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last entity in
     * a sparse set. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the element following the last entity of a sparse
     * set.
     */
    [[nodiscard]] iterator end() const noexcept {
        return iterator{packed, {}};
    }

    /*! @copydoc end */
    [[nodiscard]] const_iterator cend() const noexcept {
        return end();
    }

    /**
     * @brief Returns a reverse iterator to the beginning.
     *
     * The returned iterator points to the first entity of the reversed internal
     * packed array. If the sparse set is empty, the returned iterator will be
     * equal to `rend()`.
     *
     * @return An iterator to the first entity of the reversed internal packed
     * array.
     */
    [[nodiscard]] const_reverse_iterator rbegin() const noexcept {
        return std::make_reverse_iterator(end());
    }

    /*! @copydoc rbegin */
    [[nodiscard]] const_reverse_iterator crbegin() const noexcept {
        return rbegin();
    }

    /**
     * @brief Returns a reverse iterator to the end.
     *
     * The returned iterator points to the element following the last entity in
     * the reversed sparse set. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last entity of the
     * reversed sparse set.
     */
    [[nodiscard]] reverse_iterator rend() const noexcept {
        return std::make_reverse_iterator(begin());
    }

    /*! @copydoc rend */
    [[nodiscard]] const_reverse_iterator crend() const noexcept {
        return rend();
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        return contains(entt) ? --(end() - index(entt)) : end();
    }

    /**
     * @brief Checks if a sparse set contains an entity.
     * @param entt A valid identifier.
     * @return True if the sparse set contains the entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        const auto elem = sparse_ptr(entt);
        constexpr auto cap = entity_traits::to_entity(null);
        // testing versions permits to avoid accessing the packed array
        return elem && (((~cap & entity_traits::to_integral(entt)) ^ entity_traits::to_integral(*elem)) < cap);
    }

    /**
     * @brief Returns the contained version for an identifier.
     * @param entt A valid identifier.
     * @return The version for the given identifier if present, the tombstone
     * version otherwise.
     */
    [[nodiscard]] version_type current(const entity_type entt) const noexcept {
        const auto elem = sparse_ptr(entt);
        constexpr auto fallback = entity_traits::to_version(tombstone);
        return elem ? entity_traits::to_version(*elem) : fallback;
    }

    /**
     * @brief Returns the position of an entity in a sparse set.
     *
     * @warning
     * Attempting to get the position of an entity that doesn't belong to the
     * sparse set results in undefined behavior.
     *
     * @param entt A valid identifier.
     * @return The position of the entity in the sparse set.
     */
    [[nodiscard]] size_type index(const entity_type entt) const noexcept {
        ENTT_ASSERT(contains(entt), "Set does not contain entity");
        return static_cast<size_type>(entity_traits::to_entity(sparse_ref(entt)));
    }

    /**
     * @brief Returns the entity at specified location, with bounds checking.
     * @param pos The position for which to return the entity.
     * @return The entity at specified location if any, a null entity otherwise.
     */
    [[nodiscard]] entity_type at(const size_type pos) const noexcept {
        return pos < packed.size() ? packed[pos] : null;
    }

    /**
     * @brief Returns the entity at specified location, without bounds checking.
     * @param pos The position for which to return the entity.
     * @return The entity at specified location.
     */
    [[nodiscard]] entity_type operator[](const size_type pos) const noexcept {
        ENTT_ASSERT(pos < packed.size(), "Position is out of bounds");
        return packed[pos];
    }

    /**
     * @brief Returns the element assigned to an entity, if any.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the sparse set results
     * in undefined behavior.
     *
     * @param entt A valid identifier.
     * @return An opaque pointer to the element assigned to the entity, if any.
     */
    [[nodiscard]] const void *get(const entity_type entt) const noexcept {
        return get_at(index(entt));
    }

    /*! @copydoc get */
    [[nodiscard]] void *get(const entity_type entt) noexcept {
        return const_cast<void *>(std::as_const(*this).get(entt));
    }

    /**
     * @brief Assigns an entity to a sparse set.
     *
     * @warning
     * Attempting to assign an entity that already belongs to the sparse set
     * results in undefined behavior.
     *
     * @param entt A valid identifier.
     * @param value Optional opaque value to forward to mixins, if any.
     * @return Iterator pointing to the emplaced element in case of success, the
     * `end()` iterator otherwise.
     */
    iterator emplace(const entity_type entt, const void *value = nullptr) {
        return try_emplace(entt, false, value);
    }

    /**
     * @brief Bump the version number of an entity.
     *
     * @warning
     * Attempting to bump the version of an entity that doesn't belong to the
     * sparse set results in undefined behavior.
     *
     * @param entt A valid identifier.
     */
    void bump(const entity_type entt) {
        auto &entity = sparse_ref(entt);
        ENTT_ASSERT(entt != tombstone && entity != null, "Cannot set the required version");
        entity = entity_traits::combine(entity_traits::to_integral(entity), entity_traits::to_integral(entt));
        packed[static_cast<size_type>(entity_traits::to_entity(entity))] = entt;
    }

    /**
     * @brief Assigns one or more entities to a sparse set.
     *
     * @warning
     * Attempting to assign an entity that already belongs to the sparse set
     * results in undefined behavior.
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @return Iterator pointing to the first element inserted in case of
     * success, the `end()` iterator otherwise.
     */
    template<typename It>
    iterator insert(It first, It last) {
        for(auto it = first; it != last; ++it) {
            try_emplace(*it, true);
        }

        return first == last ? end() : find(*first);
    }

    /**
     * @brief Erases an entity from a sparse set.
     *
     * @warning
     * Attempting to erase an entity that doesn't belong to the sparse set
     * results in undefined behavior.
     *
     * @param entt A valid identifier.
     */
    void erase(const entity_type entt) {
        const auto it = --(end() - index(entt));
        pop(it, it + 1u);
    }

    /**
     * @brief Erases entities from a set.
     *
     * @sa erase
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    template<typename It>
    void erase(It first, It last) {
        if constexpr(std::is_same_v<It, basic_iterator>) {
            pop(first, last);
        } else {
            for(; first != last; ++first) {
                erase(*first);
            }
        }
    }

    /**
     * @brief Removes an entity from a sparse set if it exists.
     * @param entt A valid identifier.
     * @return True if the entity is actually removed, false otherwise.
     */
    bool remove(const entity_type entt) {
        return contains(entt) && (erase(entt), true);
    }

    /**
     * @brief Removes entities from a sparse set if they exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @return The number of entities actually removed.
     */
    template<typename It>
    size_type remove(It first, It last) {
        size_type count{};

        for(; first != last; ++first) {
            count += remove(*first);
        }

        return count;
    }

    /*! @brief Removes all tombstones from the packed array of a sparse set. */
    void compact() {
        size_type from = packed.size();
        for(; from && packed[from - 1u] == tombstone; --from) {}

        for(auto *it = &free_list; *it != null && from; it = std::addressof(packed[entity_traits::to_entity(*it)])) {
            if(const size_type to = entity_traits::to_entity(*it); to < from) {
                --from;
                move_element(from, to);

                using std::swap;
                swap(packed[from], packed[to]);

                const auto entity = static_cast<typename entity_traits::entity_type>(to);
                sparse_ref(packed[to]) = entity_traits::combine(entity, entity_traits::to_integral(packed[to]));
                *it = entity_traits::combine(static_cast<typename entity_traits::entity_type>(from), entity_traits::reserved);
                for(; from && packed[from - 1u] == tombstone; --from) {}
            }
        }

        free_list = tombstone;
        packed.resize(from);
    }

    /**
     * @brief Swaps two entities in a sparse set.
     *
     * For what it's worth, this function affects both the internal sparse array
     * and the internal packed array. Users should not care of that anyway.
     *
     * @warning
     * Attempting to swap entities that don't belong to the sparse set results
     * in undefined behavior.
     *
     * @param lhs A valid identifier.
     * @param rhs A valid identifier.
     */
    void swap_elements(const entity_type lhs, const entity_type rhs) {
        ENTT_ASSERT(contains(lhs) && contains(rhs), "Set does not contain entities");

        auto &entt = sparse_ref(lhs);
        auto &other = sparse_ref(rhs);

        const auto from = entity_traits::to_entity(entt);
        const auto to = entity_traits::to_entity(other);

        // basic no-leak guarantee (with invalid state) if swapping throws
        swap_at(static_cast<size_type>(from), static_cast<size_type>(to));
        entt = entity_traits::combine(to, entity_traits::to_integral(packed[from]));
        other = entity_traits::combine(from, entity_traits::to_integral(packed[to]));

        using std::swap;
        swap(packed[from], packed[to]);
    }

    /**
     * @brief Sort the first count elements according to the given comparison
     * function.
     *
     * The comparison function object must return `true` if the first element
     * is _less_ than the second one, `false` otherwise. The signature of the
     * comparison function should be equivalent to the following:
     *
     * @code{.cpp}
     * bool(const Entity, const Entity);
     * @endcode
     *
     * Moreover, the comparison function object shall induce a
     * _strict weak ordering_ on the values.
     *
     * The sort function object must offer a member function template
     * `operator()` that accepts three arguments:
     *
     * * An iterator to the first element of the range to sort.
     * * An iterator past the last element of the range to sort.
     * * A comparison function to use to compare the elements.
     *
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param length Number of elements to sort.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename Compare, typename Sort = std_sort, typename... Args>
    void sort_n(const size_type length, Compare compare, Sort algo = Sort{}, Args &&...args) {
        ENTT_ASSERT(!(length > packed.size()), "Length exceeds the number of elements");
        ENTT_ASSERT(free_list == null, "Partial sorting with tombstones is not supported");

        algo(packed.rend() - length, packed.rend(), std::move(compare), std::forward<Args>(args)...);

        for(size_type pos{}; pos < length; ++pos) {
            auto curr = pos;
            auto next = index(packed[curr]);

            while(curr != next) {
                const auto idx = index(packed[next]);
                const auto entt = packed[curr];

                swap_at(next, idx);
                const auto entity = static_cast<typename entity_traits::entity_type>(curr);
                sparse_ref(entt) = entity_traits::combine(entity, entity_traits::to_integral(packed[curr]));
                curr = std::exchange(next, idx);
            }
        }
    }

    /**
     * @brief Sort all elements according to the given comparison function.
     *
     * @sa sort_n
     *
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename Compare, typename Sort = std_sort, typename... Args>
    void sort(Compare compare, Sort algo = Sort{}, Args &&...args) {
        compact();
        sort_n(packed.size(), std::move(compare), std::move(algo), std::forward<Args>(args)...);
    }

    /**
     * @brief Sort entities according to their order in another sparse set.
     *
     * Entities that are part of both the sparse sets are ordered internally
     * according to the order they have in `other`. All the other entities goes
     * to the end of the list and there are no guarantees on their order.<br/>
     * In other terms, this function can be used to impose the same order on two
     * sets by using one of them as a master and the other one as a slave.
     *
     * Iterating the sparse set with a couple of iterators returns elements in
     * the expected order after a call to `respect`. See `begin` and `end` for
     * more details.
     *
     * @param other The sparse sets that imposes the order of the entities.
     */
    void respect(const basic_sparse_set &other) {
        compact();

        const auto to = other.end();
        auto from = other.begin();

        for(size_type pos = packed.size() - 1; pos && from != to; ++from) {
            if(contains(*from)) {
                if(*from != packed[pos]) {
                    // basic no-leak guarantee (with invalid state) if swapping throws
                    swap_elements(packed[pos], *from);
                }

                --pos;
            }
        }
    }

    /*! @brief Clears a sparse set. */
    void clear() {
        if(const auto last = end(); free_list == null) {
            pop(begin(), last);
        } else {
            for(auto &&entity: *this) {
                // tombstone filter on itself
                if(const auto it = find(entity); it != last) {
                    pop(it, it + 1u);
                }
            }
        }

        free_list = tombstone;
        packed.clear();
    }

    /**
     * @brief Returned value type, if any.
     * @return Returned value type, if any.
     */
    const type_info &type() const noexcept {
        return *info;
    }

    /*! @brief Forwards variables to derived classes, if any. */
    virtual void bind(any) noexcept {}

private:
    sparse_container_type sparse;
    packed_container_type packed;
    const type_info *info;
    entity_type free_list;
    deletion_policy mode;
};

} // namespace entt

#endif

// #include "storage.hpp"
#ifndef ENTT_ENTITY_STORAGE_HPP
#define ENTT_ENTITY_STORAGE_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/iterator.hpp"

// #include "../core/memory.hpp"

// #include "../core/type_info.hpp"

// #include "component.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"

// #include "sparse_set.hpp"

// #include "storage_mixin.hpp"
#ifndef ENTT_ENTITY_SIGH_STORAGE_MIXIN_HPP
#define ENTT_ENTITY_SIGH_STORAGE_MIXIN_HPP

#include <utility>
// #include "../config/config.h"

// #include "../core/any.hpp"

// #include "../signal/sigh.hpp"
#ifndef ENTT_SIGNAL_SIGH_HPP
#define ENTT_SIGNAL_SIGH_HPP

#include <algorithm>
#include <functional>
#include <type_traits>
#include <utility>
#include <vector>
// #include "delegate.hpp"
#ifndef ENTT_SIGNAL_DELEGATE_HPP
#define ENTT_SIGNAL_DELEGATE_HPP

#include <cstddef>
#include <functional>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_SIGNAL_FWD_HPP
#define ENTT_SIGNAL_FWD_HPP

#include <memory>

namespace entt {

template<typename>
class delegate;

template<typename = std::allocator<void>>
class basic_dispatcher;

template<typename, typename = std::allocator<void>>
class emitter;

class connection;

struct scoped_connection;

template<typename>
class sink;

template<typename Type, typename = std::allocator<void>>
class sigh;

/*! @brief Alias declaration for the most common use case. */
using dispatcher = basic_dispatcher<>;

/*! @brief Disambiguation tag for constructors and the like. */
template<auto>
struct connect_arg_t {
    /*! @brief Default constructor. */
    explicit connect_arg_t() = default;
};

/**
 * @brief Constant of type connect_arg_t used to disambiguate calls.
 * @tparam Candidate Element to connect (likely a free or member function).
 */
template<auto Candidate>
inline constexpr connect_arg_t<Candidate> connect_arg{};

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Ret, typename... Args>
constexpr auto function_pointer(Ret (*)(Args...)) -> Ret (*)(Args...);

template<typename Ret, typename Type, typename... Args, typename Other>
constexpr auto function_pointer(Ret (*)(Type, Args...), Other &&) -> Ret (*)(Args...);

template<typename Class, typename Ret, typename... Args, typename... Other>
constexpr auto function_pointer(Ret (Class::*)(Args...), Other &&...) -> Ret (*)(Args...);

template<typename Class, typename Ret, typename... Args, typename... Other>
constexpr auto function_pointer(Ret (Class::*)(Args...) const, Other &&...) -> Ret (*)(Args...);

template<typename Class, typename Type, typename... Other>
constexpr auto function_pointer(Type Class::*, Other &&...) -> Type (*)();

template<typename... Type>
using function_pointer_t = decltype(function_pointer(std::declval<Type>()...));

template<typename... Class, typename Ret, typename... Args>
[[nodiscard]] constexpr auto index_sequence_for(Ret (*)(Args...)) {
    return std::index_sequence_for<Class..., Args...>{};
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic delegate implementation.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 */
template<typename>
class delegate;

/**
 * @brief Utility class to use to send around functions and members.
 *
 * Unmanaged delegate for function pointers and members. Users of this class are
 * in charge of disconnecting instances before deleting them.
 *
 * A delegate can be used as a general purpose invoker without memory overhead
 * for free functions possibly with payloads and bound or unbound members.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 */
template<typename Ret, typename... Args>
class delegate<Ret(Args...)> {
    template<auto Candidate, std::size_t... Index>
    [[nodiscard]] auto wrap(std::index_sequence<Index...>) noexcept {
        return [](const void *, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            return static_cast<Ret>(std::invoke(Candidate, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

    template<auto Candidate, typename Type, std::size_t... Index>
    [[nodiscard]] auto wrap(Type &, std::index_sequence<Index...>) noexcept {
        return [](const void *payload, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            return static_cast<Ret>(std::invoke(Candidate, *curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

    template<auto Candidate, typename Type, std::size_t... Index>
    [[nodiscard]] auto wrap(Type *, std::index_sequence<Index...>) noexcept {
        return [](const void *payload, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            return static_cast<Ret>(std::invoke(Candidate, curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

public:
    /*! @brief Function type of the contained target. */
    using function_type = Ret(const void *, Args...);
    /*! @brief Function type of the delegate. */
    using type = Ret(Args...);
    /*! @brief Return type of the delegate. */
    using result_type = Ret;

    /*! @brief Default constructor. */
    delegate() noexcept
        : instance{nullptr},
          fn{nullptr} {}

    /**
     * @brief Constructs a delegate with a given object or payload, if any.
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance Optional valid object that fits the purpose.
     */
    template<auto Candidate, typename... Type>
    delegate(connect_arg_t<Candidate>, Type &&...value_or_instance) noexcept {
        connect<Candidate>(std::forward<Type>(value_or_instance)...);
    }

    /**
     * @brief Constructs a delegate and connects an user defined function with
     * optional payload.
     * @param function Function to connect to the delegate.
     * @param payload User defined arbitrary data.
     */
    delegate(function_type *function, const void *payload = nullptr) noexcept {
        connect(function, payload);
    }

    /**
     * @brief Connects a free function or an unbound member to a delegate.
     * @tparam Candidate Function or member to connect to the delegate.
     */
    template<auto Candidate>
    void connect() noexcept {
        instance = nullptr;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
            fn = [](const void *, Args... args) -> Ret {
                return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
            };
        } else if constexpr(std::is_member_pointer_v<decltype(Candidate)>) {
            fn = wrap<Candidate>(internal::index_sequence_for<type_list_element_t<0, type_list<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
        } else {
            fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
        }
    }

    /**
     * @brief Connects a free function with payload or a bound member to a
     * delegate.
     *
     * The delegate isn't responsible for the connected object or the payload.
     * Users must always guarantee that the lifetime of the instance overcomes
     * the one of the delegate.<br/>
     * When used to connect a free function with payload, its signature must be
     * such that the instance is the first argument before the ones used to
     * define the delegate itself.
     *
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid reference that fits the purpose.
     */
    template<auto Candidate, typename Type>
    void connect(Type &value_or_instance) noexcept {
        instance = &value_or_instance;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type &, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
                return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }

    /**
     * @brief Connects a free function with payload or a bound member to a
     * delegate.
     *
     * @sa connect(Type &)
     *
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid pointer that fits the purpose.
     */
    template<auto Candidate, typename Type>
    void connect(Type *value_or_instance) noexcept {
        instance = value_or_instance;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type *, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
                return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }

    /**
     * @brief Connects an user defined function with optional payload to a
     * delegate.
     *
     * The delegate isn't responsible for the connected object or the payload.
     * Users must always guarantee that the lifetime of an instance overcomes
     * the one of the delegate.<br/>
     * The payload is returned as the first argument to the target function in
     * all cases.
     *
     * @param function Function to connect to the delegate.
     * @param payload User defined arbitrary data.
     */
    void connect(function_type *function, const void *payload = nullptr) noexcept {
        ENTT_ASSERT(function != nullptr, "Uninitialized function pointer");
        instance = payload;
        fn = function;
    }

    /**
     * @brief Resets a delegate.
     *
     * After a reset, a delegate cannot be invoked anymore.
     */
    void reset() noexcept {
        instance = nullptr;
        fn = nullptr;
    }

    /**
     * @brief Returns the instance or the payload linked to a delegate, if any.
     * @return An opaque pointer to the underlying data.
     */
    [[nodiscard]] const void *data() const noexcept {
        return instance;
    }

    /**
     * @brief Triggers a delegate.
     *
     * The delegate invokes the underlying function and returns the result.
     *
     * @warning
     * Attempting to trigger an invalid delegate results in undefined
     * behavior.
     *
     * @param args Arguments to use to invoke the underlying function.
     * @return The value returned by the underlying function.
     */
    Ret operator()(Args... args) const {
        ENTT_ASSERT(static_cast<bool>(*this), "Uninitialized delegate");
        return fn(instance, std::forward<Args>(args)...);
    }

    /**
     * @brief Checks whether a delegate actually stores a listener.
     * @return False if the delegate is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        // no need to also test instance
        return !(fn == nullptr);
    }

    /**
     * @brief Compares the contents of two delegates.
     * @param other Delegate with which to compare.
     * @return False if the two contents differ, true otherwise.
     */
    [[nodiscard]] bool operator==(const delegate<Ret(Args...)> &other) const noexcept {
        return fn == other.fn && instance == other.instance;
    }

private:
    const void *instance;
    function_type *fn;
};

/**
 * @brief Compares the contents of two delegates.
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @param lhs A valid delegate object.
 * @param rhs A valid delegate object.
 * @return True if the two contents differ, false otherwise.
 */
template<typename Ret, typename... Args>
[[nodiscard]] bool operator!=(const delegate<Ret(Args...)> &lhs, const delegate<Ret(Args...)> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Deduction guide.
 * @tparam Candidate Function or member to connect to the delegate.
 */
template<auto Candidate>
delegate(connect_arg_t<Candidate>) -> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;

/**
 * @brief Deduction guide.
 * @tparam Candidate Function or member to connect to the delegate.
 * @tparam Type Type of class or type of payload.
 */
template<auto Candidate, typename Type>
delegate(connect_arg_t<Candidate>, Type &&) -> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;

/**
 * @brief Deduction guide.
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 */
template<typename Ret, typename... Args>
delegate(Ret (*)(const void *, Args...), const void * = nullptr) -> delegate<Ret(Args...)>;

} // namespace entt

#endif

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Sink class.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 *
 * @tparam Type A valid signal handler type.
 */
template<typename Type>
class sink;

/**
 * @brief Unmanaged signal handler.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 *
 * @tparam Type A valid function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Allocator>
class sigh;

/**
 * @brief Unmanaged signal handler.
 *
 * It works directly with references to classes and pointers to member functions
 * as well as pointers to free functions. Users of this class are in charge of
 * disconnecting instances before deleting them.
 *
 * This class serves mainly two purposes:
 *
 * * Creating signals to use later to notify a bunch of listeners.
 * * Collecting results from a set of functions like in a voting system.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
class sigh<Ret(Args...), Allocator> {
    /*! @brief A sink is allowed to modify a signal. */
    friend class sink<sigh<Ret(Args...), Allocator>>;

    using alloc_traits = std::allocator_traits<Allocator>;
    using container_type = std::vector<delegate<Ret(Args...)>, typename alloc_traits::template rebind_alloc<delegate<Ret(Args...)>>>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Sink type. */
    using sink_type = sink<sigh<Ret(Args...), Allocator>>;

    /*! @brief Default constructor. */
    sigh() noexcept(std::is_nothrow_default_constructible_v<allocator_type> &&std::is_nothrow_constructible_v<container_type, const allocator_type &>)
        : sigh{allocator_type{}} {}

    /**
     * @brief Constructs a signal handler with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit sigh(const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, const allocator_type &>)
        : calls{allocator} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    sigh(const sigh &other) noexcept(std::is_nothrow_copy_constructible_v<container_type>)
        : calls{other.calls} {}

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    sigh(const sigh &other, const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, const container_type &, const allocator_type &>)
        : calls{other.calls, allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    sigh(sigh &&other) noexcept(std::is_nothrow_move_constructible_v<container_type>)
        : calls{std::move(other.calls)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    sigh(sigh &&other, const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, container_type &&, const allocator_type &>)
        : calls{std::move(other.calls), allocator} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This signal handler.
     */
    sigh &operator=(const sigh &other) noexcept(std::is_nothrow_copy_assignable_v<container_type>) {
        calls = other.calls;
        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This signal handler.
     */
    sigh &operator=(sigh &&other) noexcept(std::is_nothrow_move_assignable_v<container_type>) {
        calls = std::move(other.calls);
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given signal handler.
     * @param other Signal handler to exchange the content with.
     */
    void swap(sigh &other) noexcept(std::is_nothrow_swappable_v<container_type>) {
        using std::swap;
        swap(calls, other.calls);
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return calls.get_allocator();
    }

    /**
     * @brief Number of listeners connected to the signal.
     * @return Number of listeners currently connected.
     */
    [[nodiscard]] size_type size() const noexcept {
        return calls.size();
    }

    /**
     * @brief Returns false if at least a listener is connected to the signal.
     * @return True if the signal has no listeners connected, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return calls.empty();
    }

    /**
     * @brief Triggers a signal.
     *
     * All the listeners are notified. Order isn't guaranteed.
     *
     * @param args Arguments to use to invoke listeners.
     */
    void publish(Args... args) const {
        for(auto &&call: std::as_const(calls)) {
            call(args...);
        }
    }

    /**
     * @brief Collects return values from the listeners.
     *
     * The collector must expose a call operator with the following properties:
     *
     * * The return type is either `void` or such that it's convertible to
     *   `bool`. In the second case, a true value will stop the iteration.
     * * The list of parameters is empty if `Ret` is `void`, otherwise it
     *   contains a single element such that `Ret` is convertible to it.
     *
     * @tparam Func Type of collector to use, if any.
     * @param func A valid function object.
     * @param args Arguments to use to invoke listeners.
     */
    template<typename Func>
    void collect(Func func, Args... args) const {
        for(auto &&call: calls) {
            if constexpr(std::is_void_v<Ret>) {
                if constexpr(std::is_invocable_r_v<bool, Func>) {
                    call(args...);
                    if(func()) {
                        break;
                    }
                } else {
                    call(args...);
                    func();
                }
            } else {
                if constexpr(std::is_invocable_r_v<bool, Func, Ret>) {
                    if(func(call(args...))) {
                        break;
                    }
                } else {
                    func(call(args...));
                }
            }
        }
    }

private:
    container_type calls;
};

/**
 * @brief Connection class.
 *
 * Opaque object the aim of which is to allow users to release an already
 * estabilished connection without having to keep a reference to the signal or
 * the sink that generated it.
 */
class connection {
    /*! @brief A sink is allowed to create connection objects. */
    template<typename>
    friend class sink;

    connection(delegate<void(void *)> fn, void *ref)
        : disconnect{fn}, signal{ref} {}

public:
    /*! @brief Default constructor. */
    connection()
        : disconnect{},
          signal{} {}

    /**
     * @brief Checks whether a connection is properly initialized.
     * @return True if the connection is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(disconnect);
    }

    /*! @brief Breaks the connection. */
    void release() {
        if(disconnect) {
            disconnect(signal);
            disconnect.reset();
        }
    }

private:
    delegate<void(void *)> disconnect;
    void *signal;
};

/**
 * @brief Scoped connection class.
 *
 * Opaque object the aim of which is to allow users to release an already
 * estabilished connection without having to keep a reference to the signal or
 * the sink that generated it.<br/>
 * A scoped connection automatically breaks the link between the two objects
 * when it goes out of scope.
 */
struct scoped_connection {
    /*! @brief Default constructor. */
    scoped_connection() = default;

    /**
     * @brief Constructs a scoped connection from a basic connection.
     * @param other A valid connection object.
     */
    scoped_connection(const connection &other)
        : conn{other} {}

    /*! @brief Default copy constructor, deleted on purpose. */
    scoped_connection(const scoped_connection &) = delete;

    /**
     * @brief Move constructor.
     * @param other The scoped connection to move from.
     */
    scoped_connection(scoped_connection &&other) noexcept
        : conn{std::exchange(other.conn, {})} {}

    /*! @brief Automatically breaks the link on destruction. */
    ~scoped_connection() {
        conn.release();
    }

    /**
     * @brief Default copy assignment operator, deleted on purpose.
     * @return This scoped connection.
     */
    scoped_connection &operator=(const scoped_connection &) = delete;

    /**
     * @brief Move assignment operator.
     * @param other The scoped connection to move from.
     * @return This scoped connection.
     */
    scoped_connection &operator=(scoped_connection &&other) noexcept {
        conn = std::exchange(other.conn, {});
        return *this;
    }

    /**
     * @brief Acquires a connection.
     * @param other The connection object to acquire.
     * @return This scoped connection.
     */
    scoped_connection &operator=(connection other) {
        conn = std::move(other);
        return *this;
    }

    /**
     * @brief Checks whether a scoped connection is properly initialized.
     * @return True if the connection is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(conn);
    }

    /*! @brief Breaks the connection. */
    void release() {
        conn.release();
    }

private:
    connection conn;
};

/**
 * @brief Sink class.
 *
 * A sink is used to connect listeners to signals and to disconnect them.<br/>
 * The function type for a listener is the one of the signal to which it
 * belongs.
 *
 * The clear separation between a signal and a sink permits to store the former
 * as private data member without exposing the publish functionality to the
 * users of the class.
 *
 * @warning
 * Lifetime of a sink must not overcome that of the signal to which it refers.
 * In any other case, attempting to use a sink results in undefined behavior.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
class sink<sigh<Ret(Args...), Allocator>> {
    using signal_type = sigh<Ret(Args...), Allocator>;
    using difference_type = typename signal_type::container_type::difference_type;

    template<auto Candidate, typename Type>
    static void release(Type value_or_instance, void *signal) {
        sink{*static_cast<signal_type *>(signal)}.disconnect<Candidate>(value_or_instance);
    }

    template<auto Candidate>
    static void release(void *signal) {
        sink{*static_cast<signal_type *>(signal)}.disconnect<Candidate>();
    }

    auto before(delegate<Ret(Args...)> call) {
        const auto &calls = signal->calls;
        const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));

        sink other{*this};
        other.offset = calls.cend() - it;
        return other;
    }

public:
    /**
     * @brief Constructs a sink that is allowed to modify a given signal.
     * @param ref A valid reference to a signal object.
     */
    sink(sigh<Ret(Args...), Allocator> &ref) noexcept
        : offset{},
          signal{&ref} {}

    /**
     * @brief Returns false if at least a listener is connected to the sink.
     * @return True if the sink has no listeners connected, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return signal->calls.empty();
    }

    /**
     * @brief Returns a sink that connects before a given free function or an
     * unbound member.
     * @tparam Function A valid free function pointer.
     * @return A properly initialized sink object.
     */
    template<auto Function>
    [[nodiscard]] sink before() {
        delegate<Ret(Args...)> call{};
        call.template connect<Function>();
        return before(std::move(call));
    }

    /**
     * @brief Returns a sink that connects before a free function with payload
     * or a bound member.
     * @tparam Candidate Member or free function to look for.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     * @return A properly initialized sink object.
     */
    template<auto Candidate, typename Type>
    [[nodiscard]] sink before(Type &&value_or_instance) {
        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance);
        return before(std::move(call));
    }

    /**
     * @brief Returns a sink that connects before a given instance or specific
     * payload.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     * @return A properly initialized sink object.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<std::remove_pointer_t<Type>>, void>, sink>>
    [[nodiscard]] sink before(Type &value_or_instance) {
        return before(&value_or_instance);
    }

    /**
     * @brief Returns a sink that connects before a given instance or specific
     * payload.
     * @param value_or_instance A valid pointer that fits the purpose.
     * @return A properly initialized sink object.
     */
    [[nodiscard]] sink before(const void *value_or_instance) {
        sink other{*this};

        if(value_or_instance) {
            const auto &calls = signal->calls;
            const auto it = std::find_if(calls.cbegin(), calls.cend(), [value_or_instance](const auto &delegate) {
                return delegate.data() == value_or_instance;
            });

            other.offset = calls.cend() - it;
        }

        return other;
    }

    /**
     * @brief Returns a sink that connects before anything else.
     * @return A properly initialized sink object.
     */
    [[nodiscard]] sink before() {
        sink other{*this};
        other.offset = signal->calls.size();
        return other;
    }

    /**
     * @brief Connects a free function (with or without payload), a bound or an
     * unbound member to a signal.
     *
     * The signal isn't responsible for the connected object or the payload, if
     * any. Users must guarantee that the lifetime of the instance overcomes the
     * one of the signal. On the other side, the signal handler performs
     * checks to avoid multiple connections for the same function.<br/>
     * When used to connect a free function with payload, its signature must be
     * such that the instance is the first argument before the ones used to
     * define the signal itself.
     *
     * @tparam Candidate Function or member to connect to the signal.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance A valid object that fits the purpose, if any.
     * @return A properly initialized connection object.
     */
    template<auto Candidate, typename... Type>
    connection connect(Type &&...value_or_instance) {
        disconnect<Candidate>(value_or_instance...);

        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance...);
        signal->calls.insert(signal->calls.end() - offset, std::move(call));

        delegate<void(void *)> conn{};
        conn.template connect<&release<Candidate, Type...>>(value_or_instance...);
        return {std::move(conn), signal};
    }

    /**
     * @brief Disconnects a free function (with or without payload), a bound or
     * an unbound member from a signal.
     * @tparam Candidate Function or member to disconnect from the signal.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance A valid object that fits the purpose, if any.
     */
    template<auto Candidate, typename... Type>
    void disconnect(Type &&...value_or_instance) {
        auto &calls = signal->calls;
        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance...);
        calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
    }

    /**
     * @brief Disconnects free functions with payload or bound members from a
     * signal.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<std::remove_pointer_t<Type>>, void>>>
    void disconnect(Type &value_or_instance) {
        disconnect(&value_or_instance);
    }

    /**
     * @brief Disconnects free functions with payload or bound members from a
     * signal.
     * @param value_or_instance A valid object that fits the purpose.
     */
    void disconnect(const void *value_or_instance) {
        if(value_or_instance) {
            auto &calls = signal->calls;
            auto predicate = [value_or_instance](const auto &delegate) { return delegate.data() == value_or_instance; };
            calls.erase(std::remove_if(calls.begin(), calls.end(), std::move(predicate)), calls.end());
        }
    }

    /*! @brief Disconnects all the listeners from a signal. */
    void disconnect() {
        signal->calls.clear();
    }

private:
    difference_type offset;
    signal_type *signal;
};

/**
 * @brief Deduction guide.
 *
 * It allows to deduce the signal handler type of a sink directly from the
 * signal it refers to.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
sink(sigh<Ret(Args...), Allocator> &) -> sink<sigh<Ret(Args...), Allocator>>;

} // namespace entt

#endif

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Mixin type used to add signal support to storage types.
 *
 * The function type of a listener is equivalent to:
 *
 * @code{.cpp}
 * void(basic_registry<entity_type> &, entity_type);
 * @endcode
 *
 * This applies to all signals made available.
 *
 * @tparam Type The type of the underlying storage.
 */
template<typename Type>
class sigh_storage_mixin final: public Type {
    using basic_registry_type = basic_registry<typename Type::entity_type, typename Type::base_type::allocator_type>;
    using sigh_type = sigh<void(basic_registry_type &, const typename Type::entity_type), typename Type::allocator_type>;
    using basic_iterator = typename Type::basic_iterator;

    void pop(basic_iterator first, basic_iterator last) override {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");

        for(; first != last; ++first) {
            const auto entt = *first;
            destruction.publish(*owner, entt);
            const auto it = Type::find(entt);
            Type::pop(it, it + 1u);
        }
    }

    basic_iterator try_emplace(const typename basic_registry_type::entity_type entt, const bool force_back, const void *value) final {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");
        Type::try_emplace(entt, force_back, value);
        construction.publish(*owner, entt);
        return Type::find(entt);
    }

public:
    /*! @brief Allocator type. */
    using allocator_type = typename Type::allocator_type;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename Type::entity_type;
    /*! @brief Expected registry type. */
    using registry_type = basic_registry_type;

    /*! @brief Default constructor. */
    sigh_storage_mixin()
        : sigh_storage_mixin{allocator_type{}} {}

    /**
     * @brief Constructs an empty storage with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit sigh_storage_mixin(const allocator_type &allocator)
        : Type{allocator},
          owner{},
          construction{allocator},
          destruction{allocator},
          update{allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    sigh_storage_mixin(sigh_storage_mixin &&other) noexcept
        : Type{std::move(other)},
          owner{other.owner},
          construction{std::move(other.construction)},
          destruction{std::move(other.destruction)},
          update{std::move(other.update)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    sigh_storage_mixin(sigh_storage_mixin &&other, const allocator_type &allocator) noexcept
        : Type{std::move(other), allocator},
          owner{other.owner},
          construction{std::move(other.construction), allocator},
          destruction{std::move(other.destruction), allocator},
          update{std::move(other.update), allocator} {}

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This storage.
     */
    sigh_storage_mixin &operator=(sigh_storage_mixin &&other) noexcept {
        Type::operator=(std::move(other));
        owner = other.owner;
        construction = std::move(other.construction);
        destruction = std::move(other.destruction);
        update = std::move(other.update);
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given storage.
     * @param other Storage to exchange the content with.
     */
    void swap(sigh_storage_mixin &other) {
        using std::swap;
        Type::swap(other);
        swap(owner, other.owner);
        swap(construction, other.construction);
        swap(destruction, other.destruction);
        swap(update, other.update);
    }

    /**
     * @brief Returns a sink object.
     *
     * The sink returned by this function can be used to receive notifications
     * whenever a new instance is created and assigned to an entity.<br/>
     * Listeners are invoked after the object has been assigned to the entity.
     *
     * @sa sink
     *
     * @return A temporary sink object.
     */
    [[nodiscard]] auto on_construct() noexcept {
        return sink{construction};
    }

    /**
     * @brief Returns a sink object.
     *
     * The sink returned by this function can be used to receive notifications
     * whenever an instance is explicitly updated.<br/>
     * Listeners are invoked after the object has been updated.
     *
     * @sa sink
     *
     * @return A temporary sink object.
     */
    [[nodiscard]] auto on_update() noexcept {
        return sink{update};
    }

    /**
     * @brief Returns a sink object.
     *
     * The sink returned by this function can be used to receive notifications
     * whenever an instance is removed from an entity and thus destroyed.<br/>
     * Listeners are invoked before the object has been removed from the entity.
     *
     * @sa sink
     *
     * @return A temporary sink object.
     */
    [[nodiscard]] auto on_destroy() noexcept {
        return sink{destruction};
    }

    /**
     * @brief Assigns entities to a storage.
     * @tparam Args Types of arguments to use to construct the object.
     * @param entt A valid identifier.
     * @param args Parameters to use to initialize the object.
     * @return A reference to the newly created object.
     */
    template<typename... Args>
    decltype(auto) emplace(const entity_type entt, Args &&...args) {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");
        Type::emplace(entt, std::forward<Args>(args)...);
        construction.publish(*owner, entt);
        return this->get(entt);
    }

    /**
     * @brief Patches the given instance for an entity.
     * @tparam Func Types of the function objects to invoke.
     * @param entt A valid identifier.
     * @param func Valid function objects.
     * @return A reference to the patched instance.
     */
    template<typename... Func>
    decltype(auto) patch(const entity_type entt, Func &&...func) {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");
        Type::patch(entt, std::forward<Func>(func)...);
        update.publish(*owner, entt);
        return this->get(entt);
    }

    /**
     * @brief Assigns entities to a storage.
     * @tparam It Type of input iterator.
     * @tparam Args Types of arguments to use to construct the objects assigned
     * to the entities.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param args Parameters to use to initialize the objects assigned to the
     * entities.
     */
    template<typename It, typename... Args>
    void insert(It first, It last, Args &&...args) {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");
        Type::insert(first, last, std::forward<Args>(args)...);

        for(auto it = construction.empty() ? last : first; it != last; ++it) {
            construction.publish(*owner, *it);
        }
    }

    /**
     * @brief Forwards variables to derived classes, if any.
     * @param value A variable wrapped in an opaque container.
     */
    void bind(any value) noexcept final {
        auto *reg = any_cast<basic_registry_type>(&value);
        owner = reg ? reg : owner;
        Type::bind(std::move(value));
    }

private:
    basic_registry_type *owner;
    sigh_type construction;
    sigh_type destruction;
    sigh_type update;
};

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Container>
class storage_iterator final {
    friend storage_iterator<const Container>;

    using container_type = std::remove_const_t<Container>;
    using alloc_traits = std::allocator_traits<typename container_type::allocator_type>;
    using comp_traits = component_traits<std::remove_pointer_t<typename container_type::value_type>>;

    using iterator_traits = std::iterator_traits<std::conditional_t<
        std::is_const_v<Container>,
        typename alloc_traits::template rebind_traits<typename std::pointer_traits<typename container_type::value_type>::element_type>::const_pointer,
        typename alloc_traits::template rebind_traits<typename std::pointer_traits<typename container_type::value_type>::element_type>::pointer>>;

public:
    using value_type = typename iterator_traits::value_type;
    using pointer = typename iterator_traits::pointer;
    using reference = typename iterator_traits::reference;
    using difference_type = typename iterator_traits::difference_type;
    using iterator_category = std::random_access_iterator_tag;

    constexpr storage_iterator() noexcept = default;

    constexpr storage_iterator(Container *ref, const difference_type idx) noexcept
        : packed{ref},
          offset{idx} {}

    template<bool Const = std::is_const_v<Container>, typename = std::enable_if_t<Const>>
    constexpr storage_iterator(const storage_iterator<std::remove_const_t<Container>> &other) noexcept
        : storage_iterator{other.packed, other.offset} {}

    constexpr storage_iterator &operator++() noexcept {
        return --offset, *this;
    }

    constexpr storage_iterator operator++(int) noexcept {
        storage_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr storage_iterator &operator--() noexcept {
        return ++offset, *this;
    }

    constexpr storage_iterator operator--(int) noexcept {
        storage_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr storage_iterator &operator+=(const difference_type value) noexcept {
        offset -= value;
        return *this;
    }

    constexpr storage_iterator operator+(const difference_type value) const noexcept {
        storage_iterator copy = *this;
        return (copy += value);
    }

    constexpr storage_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr storage_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        const auto pos = index() - value;
        return (*packed)[pos / comp_traits::page_size][fast_mod(pos, comp_traits::page_size)];
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        const auto pos = index();
        return (*packed)[pos / comp_traits::page_size] + fast_mod(pos, comp_traits::page_size);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr difference_type index() const noexcept {
        return offset - 1;
    }

private:
    Container *packed;
    difference_type offset;
};

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return rhs.index() - lhs.index();
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator==(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator!=(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator<(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return lhs.index() > rhs.index();
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator>(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return lhs.index() < rhs.index();
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator<=(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator>=(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It, typename... Other>
class extended_storage_iterator final {
    template<typename Iter, typename... Args>
    friend class extended_storage_iterator;

public:
    using value_type = decltype(std::tuple_cat(std::make_tuple(*std::declval<It>()), std::forward_as_tuple(*std::declval<Other>()...)));
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr extended_storage_iterator()
        : it{} {}

    constexpr extended_storage_iterator(It base, Other... other)
        : it{base, other...} {}

    template<typename... Args, typename = std::enable_if_t<(!std::is_same_v<Other, Args> && ...) && (std::is_constructible_v<Other, Args> && ...)>>
    constexpr extended_storage_iterator(const extended_storage_iterator<It, Args...> &other)
        : it{other.it} {}

    constexpr extended_storage_iterator &operator++() noexcept {
        return ++std::get<It>(it), (++std::get<Other>(it), ...), *this;
    }

    constexpr extended_storage_iterator operator++(int) noexcept {
        extended_storage_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {*std::get<It>(it), *std::get<Other>(it)...};
    }

    template<typename... CLhs, typename... CRhs>
    friend constexpr bool operator==(const extended_storage_iterator<CLhs...> &, const extended_storage_iterator<CRhs...> &) noexcept;

private:
    std::tuple<It, Other...> it;
};

template<typename... CLhs, typename... CRhs>
[[nodiscard]] constexpr bool operator==(const extended_storage_iterator<CLhs...> &lhs, const extended_storage_iterator<CRhs...> &rhs) noexcept {
    return std::get<0>(lhs.it) == std::get<0>(rhs.it);
}

template<typename... CLhs, typename... CRhs>
[[nodiscard]] constexpr bool operator!=(const extended_storage_iterator<CLhs...> &lhs, const extended_storage_iterator<CRhs...> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic storage implementation.
 *
 * Internal data structures arrange elements to maximize performance. There are
 * no guarantees that objects are returned in the insertion order when iterate
 * a storage. Do not make assumption on the order in any case.
 *
 * @warning
 * Empty types aren't explicitly instantiated. Therefore, many of the functions
 * normally available for non-empty types will not be available for empty ones.
 *
 * @tparam Type Type of objects assigned to the entities.
 * @tparam Entity A valid entity type (see entt_traits for more details).
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Entity, typename Allocator, typename>
class basic_storage: public basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>> {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using underlying_type = basic_sparse_set<Entity, typename alloc_traits::template rebind_alloc<Entity>>;
    using container_type = std::vector<typename alloc_traits::pointer, typename alloc_traits::template rebind_alloc<typename alloc_traits::pointer>>;
    using comp_traits = component_traits<Type>;

    static constexpr bool is_pinned_type_v = !(std::is_move_constructible_v<Type> && std::is_move_assignable_v<Type>);

    [[nodiscard]] auto &element_at(const std::size_t pos) const {
        return packed.first()[pos / comp_traits::page_size][fast_mod(pos, comp_traits::page_size)];
    }

    auto assure_at_least(const std::size_t pos) {
        auto &&container = packed.first();
        const auto idx = pos / comp_traits::page_size;

        if(!(idx < container.size())) {
            auto curr = container.size();
            container.resize(idx + 1u, nullptr);

            ENTT_TRY {
                for(const auto last = container.size(); curr < last; ++curr) {
                    container[curr] = alloc_traits::allocate(packed.second(), comp_traits::page_size);
                }
            }
            ENTT_CATCH {
                container.resize(curr);
                ENTT_THROW;
            }
        }

        return container[idx] + fast_mod(pos, comp_traits::page_size);
    }

    template<typename... Args>
    auto emplace_element(const Entity entt, const bool force_back, Args &&...args) {
        const auto it = base_type::try_emplace(entt, force_back);

        ENTT_TRY {
            auto elem = assure_at_least(static_cast<size_type>(it.index()));
            entt::uninitialized_construct_using_allocator(to_address(elem), packed.second(), std::forward<Args>(args)...);
        }
        ENTT_CATCH {
            base_type::pop(it, it + 1u);
            ENTT_THROW;
        }

        return it;
    }

    void shrink_to_size(const std::size_t sz) {
        for(auto pos = sz, length = base_type::size(); pos < length; ++pos) {
            if constexpr(comp_traits::in_place_delete) {
                if(base_type::at(pos) != tombstone) {
                    std::destroy_at(std::addressof(element_at(pos)));
                }
            } else {
                std::destroy_at(std::addressof(element_at(pos)));
            }
        }

        auto &&container = packed.first();
        auto page_allocator{packed.second()};
        const auto from = (sz + comp_traits::page_size - 1u) / comp_traits::page_size;

        for(auto pos = from, last = container.size(); pos < last; ++pos) {
            alloc_traits::deallocate(page_allocator, container[pos], comp_traits::page_size);
        }

        container.resize(from);
    }

private:
    const void *get_at(const std::size_t pos) const final {
        return std::addressof(element_at(pos));
    }

    void swap_at([[maybe_unused]] const std::size_t lhs, [[maybe_unused]] const std::size_t rhs) final {
        // use a runtime value to avoid compile-time suppression that drives the code coverage tool crazy
        ENTT_ASSERT((lhs + 1u) && !is_pinned_type_v, "Pinned type");

        if constexpr(!is_pinned_type_v) {
            using std::swap;
            swap(element_at(lhs), element_at(rhs));
        }
    }

    void move_element([[maybe_unused]] const std::size_t from, [[maybe_unused]] const std::size_t to) final {
        // use a runtime value to avoid compile-time suppression that drives the code coverage tool crazy
        ENTT_ASSERT((from + 1u) && !is_pinned_type_v, "Pinned type");

        if constexpr(!is_pinned_type_v) {
            auto &elem = element_at(from);
            entt::uninitialized_construct_using_allocator(to_address(assure_at_least(to)), packed.second(), std::move(elem));
            std::destroy_at(std::addressof(elem));
        }
    }

protected:
    /*! @brief Random access iterator type. */
    using basic_iterator = typename underlying_type::basic_iterator;

    /**
     * @brief Erases entities from a sparse set.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    void pop(basic_iterator first, basic_iterator last) override {
        for(; first != last; ++first) {
            // cannot use first.index() because it would break with cross iterators
            auto &elem = element_at(base_type::index(*first));

            if constexpr(comp_traits::in_place_delete) {
                base_type::in_place_pop(first);
                std::destroy_at(std::addressof(elem));
            } else {
                auto &other = element_at(base_type::size() - 1u);
                // destroying on exit allows reentrant destructors
                [[maybe_unused]] auto unused = std::exchange(elem, std::move(other));
                std::destroy_at(std::addressof(other));
                base_type::swap_and_pop(first);
            }
        }
    }

    /**
     * @brief Assigns an entity to a storage.
     * @param entt A valid identifier.
     * @param value Optional opaque value.
     * @param force_back Force back insertion.
     * @return Iterator pointing to the emplaced element.
     */
    basic_iterator try_emplace([[maybe_unused]] const Entity entt, [[maybe_unused]] const bool force_back, const void *value) override {
        if(value) {
            if constexpr(std::is_copy_constructible_v<value_type>) {
                return emplace_element(entt, force_back, *static_cast<const value_type *>(value));
            } else {
                return base_type::end();
            }
        } else {
            if constexpr(std::is_default_constructible_v<value_type>) {
                return emplace_element(entt, force_back);
            } else {
                return base_type::end();
            }
        }
    }

public:
    /*! @brief Base type. */
    using base_type = underlying_type;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Type of the objects assigned to entities. */
    using value_type = Type;
    /*! @brief Underlying entity identifier. */
    using entity_type = Entity;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Pointer type to contained elements. */
    using pointer = typename container_type::pointer;
    /*! @brief Constant pointer type to contained elements. */
    using const_pointer = typename alloc_traits::template rebind_traits<typename alloc_traits::const_pointer>::const_pointer;
    /*! @brief Random access iterator type. */
    using iterator = internal::storage_iterator<container_type>;
    /*! @brief Constant random access iterator type. */
    using const_iterator = internal::storage_iterator<const container_type>;
    /*! @brief Reverse iterator type. */
    using reverse_iterator = std::reverse_iterator<iterator>;
    /*! @brief Constant reverse iterator type. */
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
    /*! @brief Extended iterable storage proxy. */
    using iterable = iterable_adaptor<internal::extended_storage_iterator<typename base_type::iterator, iterator>>;
    /*! @brief Constant extended iterable storage proxy. */
    using const_iterable = iterable_adaptor<internal::extended_storage_iterator<typename base_type::const_iterator, const_iterator>>;

    /*! @brief Default constructor. */
    basic_storage()
        : basic_storage{allocator_type{}} {}

    /**
     * @brief Constructs an empty storage with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_storage(const allocator_type &allocator)
        : base_type{type_id<value_type>(), deletion_policy{comp_traits::in_place_delete}, allocator},
          packed{container_type{allocator}, allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_storage(basic_storage &&other) noexcept
        : base_type{std::move(other)},
          packed{std::move(other.packed)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_storage(basic_storage &&other, const allocator_type &allocator) noexcept
        : base_type{std::move(other), allocator},
          packed{container_type{std::move(other.packed.first()), allocator}, allocator} {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || packed.second() == other.packed.second(), "Copying a storage is not allowed");
    }

    /*! @brief Default destructor. */
    ~basic_storage() override {
        shrink_to_size(0u);
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This storage.
     */
    basic_storage &operator=(basic_storage &&other) noexcept {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || packed.second() == other.packed.second(), "Copying a storage is not allowed");

        shrink_to_size(0u);
        base_type::operator=(std::move(other));
        packed.first() = std::move(other.packed.first());
        propagate_on_container_move_assignment(packed.second(), other.packed.second());
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given storage.
     * @param other Storage to exchange the content with.
     */
    void swap(basic_storage &other) {
        using std::swap;
        underlying_type::swap(other);
        propagate_on_container_swap(packed.second(), other.packed.second());
        swap(packed.first(), other.packed.first());
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return allocator_type{packed.second()};
    }

    /**
     * @brief Increases the capacity of a storage.
     *
     * If the new capacity is greater than the current capacity, new storage is
     * allocated, otherwise the method does nothing.
     *
     * @param cap Desired capacity.
     */
    void reserve(const size_type cap) override {
        if(cap != 0u) {
            base_type::reserve(cap);
            assure_at_least(cap - 1u);
        }
    }

    /**
     * @brief Returns the number of elements that a storage has currently
     * allocated space for.
     * @return Capacity of the storage.
     */
    [[nodiscard]] size_type capacity() const noexcept override {
        return packed.first().size() * comp_traits::page_size;
    }

    /*! @brief Requests the removal of unused capacity. */
    void shrink_to_fit() override {
        base_type::shrink_to_fit();
        shrink_to_size(base_type::size());
    }

    /**
     * @brief Direct access to the array of objects.
     * @return A pointer to the array of objects.
     */
    [[nodiscard]] const_pointer raw() const noexcept {
        return packed.first().data();
    }

    /*! @copydoc raw */
    [[nodiscard]] pointer raw() noexcept {
        return packed.first().data();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the storage is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        const auto pos = static_cast<typename iterator::difference_type>(base_type::size());
        return const_iterator{&packed.first(), pos};
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        const auto pos = static_cast<typename iterator::difference_type>(base_type::size());
        return iterator{&packed.first(), pos};
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return const_iterator{&packed.first(), {}};
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return iterator{&packed.first(), {}};
    }

    /**
     * @brief Returns a reverse iterator to the beginning.
     *
     * The returned iterator points to the first instance of the reversed
     * internal array. If the storage is empty, the returned iterator will be
     * equal to `rend()`.
     *
     * @return An iterator to the first instance of the reversed internal array.
     */
    [[nodiscard]] const_reverse_iterator crbegin() const noexcept {
        return std::make_reverse_iterator(cend());
    }

    /*! @copydoc crbegin */
    [[nodiscard]] const_reverse_iterator rbegin() const noexcept {
        return crbegin();
    }

    /*! @copydoc rbegin */
    [[nodiscard]] reverse_iterator rbegin() noexcept {
        return std::make_reverse_iterator(end());
    }

    /**
     * @brief Returns a reverse iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the reversed internal array. Attempting to dereference the returned
     * iterator results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * reversed internal array.
     */
    [[nodiscard]] const_reverse_iterator crend() const noexcept {
        return std::make_reverse_iterator(cbegin());
    }

    /*! @copydoc crend */
    [[nodiscard]] const_reverse_iterator rend() const noexcept {
        return crend();
    }

    /*! @copydoc rend */
    [[nodiscard]] reverse_iterator rend() noexcept {
        return std::make_reverse_iterator(begin());
    }

    /**
     * @brief Returns the object assigned to an entity.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the storage results in
     * undefined behavior.
     *
     * @param entt A valid identifier.
     * @return The object assigned to the entity.
     */
    [[nodiscard]] const value_type &get(const entity_type entt) const noexcept {
        return element_at(base_type::index(entt));
    }

    /*! @copydoc get */
    [[nodiscard]] value_type &get(const entity_type entt) noexcept {
        return const_cast<value_type &>(std::as_const(*this).get(entt));
    }

    /**
     * @brief Returns the object assigned to an entity as a tuple.
     * @param entt A valid identifier.
     * @return The object assigned to the entity as a tuple.
     */
    [[nodiscard]] std::tuple<const value_type &> get_as_tuple(const entity_type entt) const noexcept {
        return std::forward_as_tuple(get(entt));
    }

    /*! @copydoc get_as_tuple */
    [[nodiscard]] std::tuple<value_type &> get_as_tuple(const entity_type entt) noexcept {
        return std::forward_as_tuple(get(entt));
    }

    /**
     * @brief Assigns an entity to a storage and constructs its object.
     *
     * @warning
     * Attempting to use an entity that already belongs to the storage results
     * in undefined behavior.
     *
     * @tparam Args Types of arguments to use to construct the object.
     * @param entt A valid identifier.
     * @param args Parameters to use to construct an object for the entity.
     * @return A reference to the newly created object.
     */
    template<typename... Args>
    value_type &emplace(const entity_type entt, Args &&...args) {
        if constexpr(std::is_aggregate_v<value_type>) {
            const auto it = emplace_element(entt, false, Type{std::forward<Args>(args)...});
            return element_at(static_cast<size_type>(it.index()));
        } else {
            const auto it = emplace_element(entt, false, std::forward<Args>(args)...);
            return element_at(static_cast<size_type>(it.index()));
        }
    }

    /**
     * @brief Updates the instance assigned to a given entity in-place.
     * @tparam Func Types of the function objects to invoke.
     * @param entt A valid identifier.
     * @param func Valid function objects.
     * @return A reference to the updated instance.
     */
    template<typename... Func>
    value_type &patch(const entity_type entt, Func &&...func) {
        const auto idx = base_type::index(entt);
        auto &elem = element_at(idx);
        (std::forward<Func>(func)(elem), ...);
        return elem;
    }

    /**
     * @brief Assigns one or more entities to a storage and constructs their
     * objects from a given instance.
     *
     * @warning
     * Attempting to assign an entity that already belongs to the storage
     * results in undefined behavior.
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param value An instance of the object to construct.
     */
    template<typename It>
    void insert(It first, It last, const value_type &value = {}) {
        for(; first != last; ++first) {
            emplace_element(*first, true, value);
        }
    }

    /**
     * @brief Assigns one or more entities to a storage and constructs their
     * objects from a given range.
     *
     * @sa construct
     *
     * @tparam EIt Type of input iterator.
     * @tparam CIt Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param from An iterator to the first element of the range of objects.
     */
    template<typename EIt, typename CIt, typename = std::enable_if_t<std::is_same_v<typename std::iterator_traits<CIt>::value_type, value_type>>>
    void insert(EIt first, EIt last, CIt from) {
        for(; first != last; ++first, ++from) {
            emplace_element(*first, true, *from);
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a storage.
     *
     * The iterable object returns a tuple that contains the current entity and
     * a reference to its component.
     *
     * @return An iterable object to use to _visit_ the storage.
     */
    [[nodiscard]] iterable each() noexcept {
        return {internal::extended_storage_iterator{base_type::begin(), begin()}, internal::extended_storage_iterator{base_type::end(), end()}};
    }

    /*! @copydoc each */
    [[nodiscard]] const_iterable each() const noexcept {
        return {internal::extended_storage_iterator{base_type::cbegin(), cbegin()}, internal::extended_storage_iterator{base_type::cend(), cend()}};
    }

private:
    compressed_pair<container_type, allocator_type> packed;
};

/*! @copydoc basic_storage */
template<typename Type, typename Entity, typename Allocator>
class basic_storage<Type, Entity, Allocator, std::enable_if_t<ignore_as_empty_v<Type>>>
    : public basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>> {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using underlying_type = basic_sparse_set<Entity, typename alloc_traits::template rebind_alloc<Entity>>;
    using comp_traits = component_traits<Type>;

public:
    /*! @brief Base type. */
    using base_type = underlying_type;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Type of the objects assigned to entities. */
    using value_type = Type;
    /*! @brief Underlying entity identifier. */
    using entity_type = Entity;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Extended iterable storage proxy. */
    using iterable = iterable_adaptor<internal::extended_storage_iterator<typename base_type::iterator>>;
    /*! @brief Constant extended iterable storage proxy. */
    using const_iterable = iterable_adaptor<internal::extended_storage_iterator<typename base_type::const_iterator>>;

    /*! @brief Default constructor. */
    basic_storage()
        : basic_storage{allocator_type{}} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_storage(const allocator_type &allocator)
        : base_type{type_id<value_type>(), deletion_policy{comp_traits::in_place_delete}, allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_storage(basic_storage &&other) noexcept = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_storage(basic_storage &&other, const allocator_type &allocator) noexcept
        : base_type{std::move(other), allocator} {}

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This storage.
     */
    basic_storage &operator=(basic_storage &&other) noexcept = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return allocator_type{base_type::get_allocator()};
    }

    /**
     * @brief Returns the object assigned to an entity, that is `void`.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the storage results in
     * undefined behavior.
     *
     * @param entt A valid identifier.
     */
    void get([[maybe_unused]] const entity_type entt) const noexcept {
        ENTT_ASSERT(base_type::contains(entt), "Storage does not contain entity");
    }

    /**
     * @brief Returns an empty tuple.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the storage results in
     * undefined behavior.
     *
     * @param entt A valid identifier.
     * @return Returns an empty tuple.
     */
    [[nodiscard]] std::tuple<> get_as_tuple([[maybe_unused]] const entity_type entt) const noexcept {
        ENTT_ASSERT(base_type::contains(entt), "Storage does not contain entity");
        return std::tuple{};
    }

    /**
     * @brief Assigns an entity to a storage and constructs its object.
     *
     * @warning
     * Attempting to use an entity that already belongs to the storage results
     * in undefined behavior.
     *
     * @tparam Args Types of arguments to use to construct the object.
     * @param entt A valid identifier.
     */
    template<typename... Args>
    void emplace(const entity_type entt, Args &&...) {
        base_type::try_emplace(entt, false);
    }

    /**
     * @brief Updates the instance assigned to a given entity in-place.
     * @tparam Func Types of the function objects to invoke.
     * @param entt A valid identifier.
     * @param func Valid function objects.
     */
    template<typename... Func>
    void patch([[maybe_unused]] const entity_type entt, Func &&...func) {
        ENTT_ASSERT(base_type::contains(entt), "Storage does not contain entity");
        (std::forward<Func>(func)(), ...);
    }

    /**
     * @brief Assigns entities to a storage.
     * @tparam It Type of input iterator.
     * @tparam Args Types of optional arguments.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    template<typename It, typename... Args>
    void insert(It first, It last, Args &&...) {
        for(; first != last; ++first) {
            base_type::try_emplace(*first, true);
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a storage.
     *
     * The iterable object returns a tuple that contains the current entity.
     *
     * @return An iterable object to use to _visit_ the storage.
     */
    [[nodiscard]] iterable each() noexcept {
        return {internal::extended_storage_iterator{base_type::begin()}, internal::extended_storage_iterator{base_type::end()}};
    }

    /*! @copydoc each */
    [[nodiscard]] const_iterable each() const noexcept {
        return {internal::extended_storage_iterator{base_type::cbegin()}, internal::extended_storage_iterator{base_type::cend()}};
    }
};

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename, typename>
class extended_group_iterator;

template<typename It, typename... Owned, typename... Get>
class extended_group_iterator<It, owned_t<Owned...>, get_t<Get...>> {
    template<typename Type>
    auto index_to_element([[maybe_unused]] Type &cpool) const {
        if constexpr(ignore_as_empty_v<typename Type::value_type>) {
            return std::make_tuple();
        } else {
            return std::forward_as_tuple(cpool.rbegin()[it.index()]);
        }
    }

public:
    using difference_type = std::ptrdiff_t;
    using value_type = decltype(std::tuple_cat(std::make_tuple(*std::declval<It>()), std::declval<Owned>().get_as_tuple({})..., std::declval<Get>().get_as_tuple({})...));
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    constexpr extended_group_iterator()
        : it{},
          pools{} {}

    extended_group_iterator(It from, const std::tuple<Owned *..., Get *...> &cpools)
        : it{from},
          pools{cpools} {}

    extended_group_iterator &operator++() noexcept {
        return ++it, *this;
    }

    extended_group_iterator operator++(int) noexcept {
        extended_group_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] reference operator*() const noexcept {
        return std::tuple_cat(std::make_tuple(*it), index_to_element(*std::get<Owned *>(pools))..., std::get<Get *>(pools)->get_as_tuple(*it)...);
    }

    [[nodiscard]] pointer operator->() const noexcept {
        return operator*();
    }

    template<typename... Lhs, typename... Rhs>
    friend constexpr bool operator==(const extended_group_iterator<Lhs...> &, const extended_group_iterator<Rhs...> &) noexcept;

private:
    It it;
    std::tuple<Owned *..., Get *...> pools;
};

template<typename... Lhs, typename... Rhs>
[[nodiscard]] constexpr bool operator==(const extended_group_iterator<Lhs...> &lhs, const extended_group_iterator<Rhs...> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename... Lhs, typename... Rhs>
[[nodiscard]] constexpr bool operator!=(const extended_group_iterator<Lhs...> &lhs, const extended_group_iterator<Rhs...> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Group.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error, but for a few reasonable cases.
 */
template<typename, typename, typename>
class basic_group;

/**
 * @brief Non-owning group.
 *
 * A non-owning group returns all entities and only the entities that are at
 * least in the given storage. Moreover, it's guaranteed that the entity list is
 * tightly packed in memory for fast iterations.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New elements are added to the storage.
 * * The entity currently pointed is modified (for example, components are added
 *   or removed from it).
 * * The entity currently pointed is destroyed.
 *
 * In all other cases, modifying the pools iterated by the group in any way
 * invalidates all the iterators and using them results in undefined behavior.
 *
 * @tparam Get Types of storage _observed_ by the group.
 * @tparam Exclude Types of storage used to filter the group.
 */
template<typename... Get, typename... Exclude>
class basic_group<owned_t<>, get_t<Get...>, exclude_t<Exclude...>> {
    using underlying_type = std::common_type_t<typename Get::entity_type..., typename Exclude::entity_type...>;
    using basic_common_type = std::common_type_t<typename Get::base_type..., typename Exclude::base_type...>;

    template<typename Type>
    static constexpr std::size_t index_of = type_list_index_v<std::remove_const_t<Type>, type_list<typename Get::value_type...>>;

public:
    /*! @brief Underlying entity identifier. */
    using entity_type = underlying_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = basic_common_type;
    /*! @brief Random access iterator type. */
    using iterator = typename base_type::iterator;
    /*! @brief Reversed iterator type. */
    using reverse_iterator = typename base_type::reverse_iterator;
    /*! @brief Iterable group type. */
    using iterable = iterable_adaptor<internal::extended_group_iterator<iterator, owned_t<>, get_t<Get...>>>;

    /*! @brief Default constructor to use to create empty, invalid groups. */
    basic_group() noexcept
        : handler{} {}

    /**
     * @brief Constructs a group from a set of storage classes.
     * @param ref The actual entities to iterate.
     * @param gpool Storage types to iterate _observed_ by the group.
     */
    basic_group(basic_common_type &ref, Get &...gpool) noexcept
        : handler{&ref},
          pools{&gpool...} {}

    /**
     * @brief Returns a const reference to the underlying handler.
     * @return A const reference to the underlying handler.
     */
    [[nodiscard]] const base_type &handle() const noexcept {
        return *handler;
    }

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Type Type of component of which to return the storage.
     * @return The storage for the given component type.
     */
    template<typename Type>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return storage<index_of<Type>>();
    }

    /**
     * @brief Returns the storage for a given index.
     * @tparam Index Index of the storage to return.
     * @return The storage for the given index.
     */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return *std::get<Index>(pools);
    }

    /**
     * @brief Returns the number of entities that are part of the group.
     * @return Number of entities that are part of the group.
     */
    [[nodiscard]] size_type size() const noexcept {
        return *this ? handler->size() : size_type{};
    }

    /**
     * @brief Returns the number of elements that a group has currently
     * allocated space for.
     * @return Capacity of the group.
     */
    [[nodiscard]] size_type capacity() const noexcept {
        return *this ? handler->capacity() : size_type{};
    }

    /*! @brief Requests the removal of unused capacity. */
    void shrink_to_fit() {
        if(*this) {
            handler->shrink_to_fit();
        }
    }

    /**
     * @brief Checks whether a group is empty.
     * @return True if the group is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return !*this || handler->empty();
    }

    /**
     * @brief Returns an iterator to the first entity of the group.
     *
     * The returned iterator points to the first entity of the group. If the
     * group is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the group.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return *this ? handler->begin() : iterator{};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the group.
     *
     * The returned iterator points to the entity following the last entity of
     * the group. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * group.
     */
    [[nodiscard]] iterator end() const noexcept {
        return *this ? handler->end() : iterator{};
    }

    /**
     * @brief Returns an iterator to the first entity of the reversed group.
     *
     * The returned iterator points to the first entity of the reversed group.
     * If the group is empty, the returned iterator will be equal to `rend()`.
     *
     * @return An iterator to the first entity of the reversed group.
     */
    [[nodiscard]] reverse_iterator rbegin() const noexcept {
        return *this ? handler->rbegin() : reverse_iterator{};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the reversed
     * group.
     *
     * The returned iterator points to the entity following the last entity of
     * the reversed group. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * reversed group.
     */
    [[nodiscard]] reverse_iterator rend() const noexcept {
        return *this ? handler->rend() : reverse_iterator{};
    }

    /**
     * @brief Returns the first entity of the group, if any.
     * @return The first entity of the group if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type front() const noexcept {
        const auto it = begin();
        return it != end() ? *it : null;
    }

    /**
     * @brief Returns the last entity of the group, if any.
     * @return The last entity of the group if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type back() const noexcept {
        const auto it = rbegin();
        return it != rend() ? *it : null;
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        const auto it = *this ? handler->find(entt) : iterator{};
        return it != end() && *it == entt ? it : end();
    }

    /**
     * @brief Returns the identifier that occupies the given position.
     * @param pos Position of the element to return.
     * @return The identifier that occupies the given position.
     */
    [[nodiscard]] entity_type operator[](const size_type pos) const {
        return begin()[pos];
    }

    /**
     * @brief Checks if a group is properly initialized.
     * @return True if the group is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return handler != nullptr;
    }

    /**
     * @brief Checks if a group contains an entity.
     * @param entt A valid identifier.
     * @return True if the group contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        return *this && handler->contains(entt);
    }

    /**
     * @brief Returns the components assigned to the given entity.
     *
     * Prefer this function instead of `registry::get` during iterations. It has
     * far better performance than its counterpart.
     *
     * @warning
     * Attempting to use an invalid component type results in a compilation
     * error. Attempting to use an entity that doesn't belong to the group
     * results in undefined behavior.
     *
     * @tparam Type Types of components to get.
     * @param entt A valid identifier.
     * @return The components assigned to the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Type) == 0) {
            return std::apply([entt](auto *...curr) { return std::tuple_cat(curr->get_as_tuple(entt)...); }, pools);
        } else if constexpr(sizeof...(Type) == 1) {
            return (std::get<index_of<Type>>(pools)->get(entt), ...);
        } else {
            return std::tuple_cat(std::get<index_of<Type>>(pools)->get_as_tuple(entt)...);
        }
    }

    /**
     * @brief Iterates entities and components and applies the given function
     * object to them.
     *
     * The function object is invoked for each entity. It is provided with the
     * entity itself and a set of references to non-empty components. The
     * _constness_ of the components is as requested.<br/>
     * The signature of the function must be equivalent to one of the following
     * forms:
     *
     * @code{.cpp}
     * void(const entity_type, Type &...);
     * void(Type &...);
     * @endcode
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        for(const auto entt: *this) {
            if constexpr(is_applicable_v<Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_group>().get({})))>) {
                std::apply(func, std::tuple_cat(std::make_tuple(entt), get(entt)));
            } else {
                std::apply(func, get(entt));
            }
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a group.
     *
     * The iterable object returns tuples that contain the current entity and a
     * set of references to its non-empty components. The _constness_ of the
     * components is as requested.
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @return An iterable object to use to _visit_ the group.
     */
    [[nodiscard]] iterable each() const noexcept {
        return iterable{{begin(), pools}, {end(), pools}};
    }

    /**
     * @brief Sort a group according to the given comparison function.
     *
     * Sort the group so that iterating it with a couple of iterators returns
     * entities and components in the expected order. See `begin` and `end` for
     * more details.
     *
     * The comparison function object must return `true` if the first element
     * is _less_ than the second one, `false` otherwise. The signature of the
     * comparison function should be equivalent to one of the following:
     *
     * @code{.cpp}
     * bool(std::tuple<Type &...>, std::tuple<Type &...>);
     * bool(const Type &..., const Type &...);
     * bool(const Entity, const Entity);
     * @endcode
     *
     * Where `Type` are such that they are iterated by the group.<br/>
     * Moreover, the comparison function object shall induce a
     * _strict weak ordering_ on the values.
     *
     * The sort function object must offer a member function template
     * `operator()` that accepts three arguments:
     *
     * * An iterator to the first element of the range to sort.
     * * An iterator past the last element of the range to sort.
     * * A comparison function to use to compare the elements.
     *
     * @tparam Type Optional types of components to compare.
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename... Type, typename Compare, typename Sort = std_sort, typename... Args>
    void sort(Compare compare, Sort algo = Sort{}, Args &&...args) {
        if(*this) {
            if constexpr(sizeof...(Type) == 0) {
                static_assert(std::is_invocable_v<Compare, const entity_type, const entity_type>, "Invalid comparison function");
                handler->sort(std::move(compare), std::move(algo), std::forward<Args>(args)...);
            } else {
                auto comp = [this, &compare](const entity_type lhs, const entity_type rhs) {
                    if constexpr(sizeof...(Type) == 1) {
                        return compare((std::get<index_of<Type>>(pools)->get(lhs), ...), (std::get<index_of<Type>>(pools)->get(rhs), ...));
                    } else {
                        return compare(std::forward_as_tuple(std::get<index_of<Type>>(pools)->get(lhs)...), std::forward_as_tuple(std::get<index_of<Type>>(pools)->get(rhs)...));
                    }
                };

                handler->sort(std::move(comp), std::move(algo), std::forward<Args>(args)...);
            }
        }
    }

    /**
     * @brief Sort the shared pool of entities according to the given component.
     *
     * Non-owning groups of the same type share with the registry a pool of
     * entities with its own order that doesn't depend on the order of any pool
     * of components. Users can order the underlying data structure so that it
     * respects the order of the pool of the given component.
     *
     * @note
     * The shared pool of entities and thus its order is affected by the changes
     * to each and every pool that it tracks. Therefore changes to those pools
     * can quickly ruin the order imposed to the pool of entities shared between
     * the non-owning groups.
     *
     * @tparam Type Type of component to use to impose the order.
     */
    template<typename Type>
    void sort() const {
        if(*this) {
            handler->respect(*std::get<index_of<Type>>(pools));
        }
    }

private:
    base_type *const handler;
    const std::tuple<Get *...> pools;
};

/**
 * @brief Owning group.
 *
 * Owning groups returns all entities and only the entities that are at
 * least in the given storage. Moreover:
 *
 * * It's guaranteed that the entity list is tightly packed in memory for fast
 *   iterations.
 * * It's guaranteed that all components in the owned storage are tightly packed
 *   in memory for even faster iterations and to allow direct access.
 * * They stay true to the order of the owned storage and all instances have the
 *   same order in memory.
 *
 * The more types of storage are owned, the faster it is to iterate a group.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New elements are added to the storage.
 * * The entity currently pointed is modified (for example, components are added
 *   or removed from it).
 * * The entity currently pointed is destroyed.
 *
 * In all other cases, modifying the pools iterated by the group in any way
 * invalidates all the iterators and using them results in undefined behavior.
 *
 * @tparam Owned Types of storage _owned_ by the group.
 * @tparam Get Types of storage _observed_ by the group.
 * @tparam Exclude Types of storage used to filter the group.
 */
template<typename... Owned, typename... Get, typename... Exclude>
class basic_group<owned_t<Owned...>, get_t<Get...>, exclude_t<Exclude...>> {
    using underlying_type = std::common_type_t<typename Owned::entity_type..., typename Get::entity_type..., typename Exclude::entity_type...>;
    using basic_common_type = std::common_type_t<typename Owned::base_type..., typename Get::base_type..., typename Exclude::base_type...>;

    template<typename Type>
    static constexpr std::size_t index_of = type_list_index_v<std::remove_const_t<Type>, type_list<typename Owned::value_type..., typename Get::value_type...>>;

public:
    /*! @brief Underlying entity identifier. */
    using entity_type = underlying_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = basic_common_type;
    /*! @brief Random access iterator type. */
    using iterator = typename base_type::iterator;
    /*! @brief Reversed iterator type. */
    using reverse_iterator = typename base_type::reverse_iterator;
    /*! @brief Iterable group type. */
    using iterable = iterable_adaptor<internal::extended_group_iterator<iterator, owned_t<Owned...>, get_t<Get...>>>;

    /*! @brief Default constructor to use to create empty, invalid groups. */
    basic_group() noexcept
        : length{} {}

    /**
     * @brief Constructs a group from a set of storage classes.
     * @param extent The actual number of entities to iterate.
     * @param opool Storage types to iterate _owned_ by the group.
     * @param gpool Storage types to iterate _observed_ by the group.
     */
    basic_group(const std::size_t &extent, Owned &...opool, Get &...gpool) noexcept
        : pools{&opool..., &gpool...},
          length{&extent} {}

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Type Type of component of which to return the storage.
     * @return The storage for the given component type.
     */
    template<typename Type>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return storage<index_of<Type>>();
    }

    /**
     * @brief Returns the storage for a given index.
     * @tparam Index Index of the storage to return.
     * @return The storage for the given index.
     */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return *std::get<Index>(pools);
    }

    /**
     * @brief Returns the number of entities that that are part of the group.
     * @return Number of entities that that are part of the group.
     */
    [[nodiscard]] size_type size() const noexcept {
        return *this ? *length : size_type{};
    }

    /**
     * @brief Checks whether a group is empty.
     * @return True if the group is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return !*this || !*length;
    }

    /**
     * @brief Returns an iterator to the first entity of the group.
     *
     * The returned iterator points to the first entity of the group. If the
     * group is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the group.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return *this ? (std::get<0>(pools)->base_type::end() - *length) : iterator{};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the group.
     *
     * The returned iterator points to the entity following the last entity of
     * the group. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * group.
     */
    [[nodiscard]] iterator end() const noexcept {
        return *this ? std::get<0>(pools)->base_type::end() : iterator{};
    }

    /**
     * @brief Returns an iterator to the first entity of the reversed group.
     *
     * The returned iterator points to the first entity of the reversed group.
     * If the group is empty, the returned iterator will be equal to `rend()`.
     *
     * @return An iterator to the first entity of the reversed group.
     */
    [[nodiscard]] reverse_iterator rbegin() const noexcept {
        return *this ? std::get<0>(pools)->base_type::rbegin() : reverse_iterator{};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the reversed
     * group.
     *
     * The returned iterator points to the entity following the last entity of
     * the reversed group. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * reversed group.
     */
    [[nodiscard]] reverse_iterator rend() const noexcept {
        return *this ? (std::get<0>(pools)->base_type::rbegin() + *length) : reverse_iterator{};
    }

    /**
     * @brief Returns the first entity of the group, if any.
     * @return The first entity of the group if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type front() const noexcept {
        const auto it = begin();
        return it != end() ? *it : null;
    }

    /**
     * @brief Returns the last entity of the group, if any.
     * @return The last entity of the group if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type back() const noexcept {
        const auto it = rbegin();
        return it != rend() ? *it : null;
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        const auto it = *this ? std::get<0>(pools)->find(entt) : iterator{};
        return it != end() && it >= begin() && *it == entt ? it : end();
    }

    /**
     * @brief Returns the identifier that occupies the given position.
     * @param pos Position of the element to return.
     * @return The identifier that occupies the given position.
     */
    [[nodiscard]] entity_type operator[](const size_type pos) const {
        return begin()[pos];
    }

    /**
     * @brief Checks if a group is properly initialized.
     * @return True if the group is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return length != nullptr;
    }

    /**
     * @brief Checks if a group contains an entity.
     * @param entt A valid identifier.
     * @return True if the group contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        return *this && std::get<0>(pools)->contains(entt) && (std::get<0>(pools)->index(entt) < (*length));
    }

    /**
     * @brief Returns the components assigned to the given entity.
     *
     * Prefer this function instead of `registry::get` during iterations. It has
     * far better performance than its counterpart.
     *
     * @warning
     * Attempting to use an invalid component type results in a compilation
     * error. Attempting to use an entity that doesn't belong to the group
     * results in undefined behavior.
     *
     * @tparam Type Types of components to get.
     * @param entt A valid identifier.
     * @return The components assigned to the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Type) == 0) {
            return std::apply([entt](auto *...curr) { return std::tuple_cat(curr->get_as_tuple(entt)...); }, pools);
        } else if constexpr(sizeof...(Type) == 1) {
            return (std::get<index_of<Type>>(pools)->get(entt), ...);
        } else {
            return std::tuple_cat(std::get<index_of<Type>>(pools)->get_as_tuple(entt)...);
        }
    }

    /**
     * @brief Iterates entities and components and applies the given function
     * object to them.
     *
     * The function object is invoked for each entity. It is provided with the
     * entity itself and a set of references to non-empty components. The
     * _constness_ of the components is as requested.<br/>
     * The signature of the function must be equivalent to one of the following
     * forms:
     *
     * @code{.cpp}
     * void(const entity_type, Type &...);
     * void(Type &...);
     * @endcode
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        for(auto args: each()) {
            if constexpr(is_applicable_v<Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_group>().get({})))>) {
                std::apply(func, args);
            } else {
                std::apply([&func](auto, auto &&...less) { func(std::forward<decltype(less)>(less)...); }, args);
            }
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a group.
     *
     * The iterable object returns tuples that contain the current entity and a
     * set of references to its non-empty components. The _constness_ of the
     * components is as requested.
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @return An iterable object to use to _visit_ the group.
     */
    [[nodiscard]] iterable each() const noexcept {
        return {{begin(), pools}, {end(), pools}};
    }

    /**
     * @brief Sort a group according to the given comparison function.
     *
     * Sort the group so that iterating it with a couple of iterators returns
     * entities and components in the expected order. See `begin` and `end` for
     * more details.
     *
     * The comparison function object must return `true` if the first element
     * is _less_ than the second one, `false` otherwise. The signature of the
     * comparison function should be equivalent to one of the following:
     *
     * @code{.cpp}
     * bool(std::tuple<Type &...>, std::tuple<Type &...>);
     * bool(const Type &, const Type &);
     * bool(const Entity, const Entity);
     * @endcode
     *
     * Where `Type` are either owned types or not but still such that they are
     * iterated by the group.<br/>
     * Moreover, the comparison function object shall induce a
     * _strict weak ordering_ on the values.
     *
     * The sort function object must offer a member function template
     * `operator()` that accepts three arguments:
     *
     * * An iterator to the first element of the range to sort.
     * * An iterator past the last element of the range to sort.
     * * A comparison function to use to compare the elements.
     *
     * @tparam Type Optional types of components to compare.
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename... Type, typename Compare, typename Sort = std_sort, typename... Args>
    void sort(Compare compare, Sort algo = Sort{}, Args &&...args) const {
        if constexpr(sizeof...(Type) == 0) {
            static_assert(std::is_invocable_v<Compare, const entity_type, const entity_type>, "Invalid comparison function");
            std::get<0>(pools)->sort_n(*length, std::move(compare), std::move(algo), std::forward<Args>(args)...);
        } else {
            auto comp = [this, &compare](const entity_type lhs, const entity_type rhs) {
                if constexpr(sizeof...(Type) == 1) {
                    return compare((std::get<index_of<Type>>(pools)->get(lhs), ...), (std::get<index_of<Type>>(pools)->get(rhs), ...));
                } else {
                    return compare(std::forward_as_tuple(std::get<index_of<Type>>(pools)->get(lhs)...), std::forward_as_tuple(std::get<index_of<Type>>(pools)->get(rhs)...));
                }
            };

            std::get<0>(pools)->sort_n(*length, std::move(comp), std::move(algo), std::forward<Args>(args)...);
        }

        std::apply([this](auto *head, auto *...other) {
            for(auto next = *length; next; --next) {
                const auto pos = next - 1;
                [[maybe_unused]] const auto entt = head->data()[pos];
                (other->swap_elements(other->data()[pos], entt), ...);
            }
        },
                   pools);
    }

private:
    const std::tuple<Owned *..., Get *...> pools;
    const size_type *const length;
};

} // namespace entt

#endif

// #include "entity/handle.hpp"
#ifndef ENTT_ENTITY_HANDLE_HPP
#define ENTT_ENTITY_HANDLE_HPP

#include <iterator>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../core/iterator.hpp"

// #include "../core/type_traits.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class handle_storage_iterator final {
    template<typename Other>
    friend class handle_storage_iterator;

    using underlying_type = std::remove_reference_t<typename It::value_type::second_type>;
    using entity_type = typename underlying_type::entity_type;

public:
    using value_type = typename std::iterator_traits<It>::value_type;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr handle_storage_iterator() noexcept
        : entt{null},
          it{},
          last{} {}

    constexpr handle_storage_iterator(entity_type value, It from, It to) noexcept
        : entt{value},
          it{from},
          last{to} {
        while(it != last && !it->second.contains(entt)) { ++it; }
    }

    constexpr handle_storage_iterator &operator++() noexcept {
        while(++it != last && !it->second.contains(entt)) {}
        return *this;
    }

    constexpr handle_storage_iterator operator++(int) noexcept {
        handle_storage_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *it;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const handle_storage_iterator<ILhs> &, const handle_storage_iterator<IRhs> &) noexcept;

private:
    entity_type entt;
    It it;
    It last;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const handle_storage_iterator<ILhs> &lhs, const handle_storage_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const handle_storage_iterator<ILhs> &lhs, const handle_storage_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Non-owning handle to an entity.
 *
 * Tiny wrapper around a registry and an entity.
 *
 * @tparam Registry Basic registry type.
 * @tparam Scope Types to which to restrict the scope of a handle.
 */
template<typename Registry, typename... Scope>
struct basic_handle {
    /*! @brief Type of registry accepted by the handle. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename registry_type::entity_type;
    /*! @brief Underlying version type. */
    using version_type = typename registry_type::version_type;
    /*! @brief Unsigned integer type. */
    using size_type = typename registry_type::size_type;

    /*! @brief Constructs an invalid handle. */
    basic_handle() noexcept
        : reg{},
          entt{null} {}

    /**
     * @brief Constructs a handle from a given registry and entity.
     * @param ref An instance of the registry class.
     * @param value A valid identifier.
     */
    basic_handle(registry_type &ref, entity_type value) noexcept
        : reg{&ref},
          entt{value} {}

    /**
     * @brief Returns an iterable object to use to _visit_ a handle.
     *
     * The iterable object returns a pair that contains the name and a reference
     * to the current storage.<br/>
     * Returned storage are those that contain the entity associated with the
     * handle.
     *
     * @return An iterable object to use to _visit_ the handle.
     */
    [[nodiscard]] auto storage() const noexcept {
        auto iterable = reg->storage();
        using iterator_type = internal::handle_storage_iterator<typename decltype(iterable)::iterator>;
        return iterable_adaptor{iterator_type{entt, iterable.begin(), iterable.end()}, iterator_type{entt, iterable.end(), iterable.end()}};
    }

    /**
     * @brief Constructs a const handle from a non-const one.
     * @tparam Other A valid entity type (see entt_traits for more details).
     * @tparam Args Scope of the handle to construct.
     * @return A const handle referring to the same registry and the same
     * entity.
     */
    template<typename Other, typename... Args>
    operator basic_handle<Other, Args...>() const noexcept {
        static_assert(std::is_same_v<Other, Registry> || std::is_same_v<std::remove_const_t<Other>, Registry>, "Invalid conversion between different handles");
        static_assert((sizeof...(Scope) == 0 || ((sizeof...(Args) != 0 && sizeof...(Args) <= sizeof...(Scope)) && ... && (type_list_contains_v<type_list<Scope...>, Args>))), "Invalid conversion between different handles");

        return reg ? basic_handle<Other, Args...>{*reg, entt} : basic_handle<Other, Args...>{};
    }

    /**
     * @brief Converts a handle to its underlying entity.
     * @return The contained identifier.
     */
    [[nodiscard]] operator entity_type() const noexcept {
        return entity();
    }

    /**
     * @brief Checks if a handle refers to non-null registry pointer and entity.
     * @return True if the handle refers to non-null registry and entity, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return reg && reg->valid(entt);
    }

    /**
     * @brief Checks if a handle refers to a valid entity or not.
     * @return True if the handle refers to a valid entity, false otherwise.
     */
    [[nodiscard]] bool valid() const {
        return reg->valid(entt);
    }

    /**
     * @brief Returns a pointer to the underlying registry, if any.
     * @return A pointer to the underlying registry, if any.
     */
    [[nodiscard]] registry_type *registry() const noexcept {
        return reg;
    }

    /**
     * @brief Returns the entity associated with a handle.
     * @return The entity associated with the handle.
     */
    [[nodiscard]] entity_type entity() const noexcept {
        return entt;
    }

    /*! @brief Destroys the entity associated with a handle. */
    void destroy() {
        reg->destroy(entt);
    }

    /**
     * @brief Destroys the entity associated with a handle.
     * @param version A desired version upon destruction.
     */
    void destroy(const version_type version) {
        reg->destroy(entt, version);
    }

    /**
     * @brief Assigns the given component to a handle.
     * @tparam Component Type of component to create.
     * @tparam Args Types of arguments to use to construct the component.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the newly created component.
     */
    template<typename Component, typename... Args>
    decltype(auto) emplace(Args &&...args) const {
        static_assert(((sizeof...(Scope) == 0) || ... || std::is_same_v<Component, Scope>), "Invalid type");
        return reg->template emplace<Component>(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Assigns or replaces the given component for a handle.
     * @tparam Component Type of component to assign or replace.
     * @tparam Args Types of arguments to use to construct the component.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the newly created component.
     */
    template<typename Component, typename... Args>
    decltype(auto) emplace_or_replace(Args &&...args) const {
        static_assert(((sizeof...(Scope) == 0) || ... || std::is_same_v<Component, Scope>), "Invalid type");
        return reg->template emplace_or_replace<Component>(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Patches the given component for a handle.
     * @tparam Component Type of component to patch.
     * @tparam Func Types of the function objects to invoke.
     * @param func Valid function objects.
     * @return A reference to the patched component.
     */
    template<typename Component, typename... Func>
    decltype(auto) patch(Func &&...func) const {
        static_assert(((sizeof...(Scope) == 0) || ... || std::is_same_v<Component, Scope>), "Invalid type");
        return reg->template patch<Component>(entt, std::forward<Func>(func)...);
    }

    /**
     * @brief Replaces the given component for a handle.
     * @tparam Component Type of component to replace.
     * @tparam Args Types of arguments to use to construct the component.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the component being replaced.
     */
    template<typename Component, typename... Args>
    decltype(auto) replace(Args &&...args) const {
        static_assert(((sizeof...(Scope) == 0) || ... || std::is_same_v<Component, Scope>), "Invalid type");
        return reg->template replace<Component>(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Removes the given components from a handle.
     * @tparam Component Types of components to remove.
     * @return The number of components actually removed.
     */
    template<typename... Component>
    size_type remove() const {
        static_assert(sizeof...(Scope) == 0 || (type_list_contains_v<type_list<Scope...>, Component> && ...), "Invalid type");
        return reg->template remove<Component...>(entt);
    }

    /**
     * @brief Erases the given components from a handle.
     * @tparam Component Types of components to erase.
     */
    template<typename... Component>
    void erase() const {
        static_assert(sizeof...(Scope) == 0 || (type_list_contains_v<type_list<Scope...>, Component> && ...), "Invalid type");
        reg->template erase<Component...>(entt);
    }

    /**
     * @brief Checks if a handle has all the given components.
     * @tparam Component Components for which to perform the check.
     * @return True if the handle has all the components, false otherwise.
     */
    template<typename... Component>
    [[nodiscard]] decltype(auto) all_of() const {
        return reg->template all_of<Component...>(entt);
    }

    /**
     * @brief Checks if a handle has at least one of the given components.
     * @tparam Component Components for which to perform the check.
     * @return True if the handle has at least one of the given components,
     * false otherwise.
     */
    template<typename... Component>
    [[nodiscard]] decltype(auto) any_of() const {
        return reg->template any_of<Component...>(entt);
    }

    /**
     * @brief Returns references to the given components for a handle.
     * @tparam Component Types of components to get.
     * @return References to the components owned by the handle.
     */
    template<typename... Component>
    [[nodiscard]] decltype(auto) get() const {
        static_assert(sizeof...(Scope) == 0 || (type_list_contains_v<type_list<Scope...>, Component> && ...), "Invalid type");
        return reg->template get<Component...>(entt);
    }

    /**
     * @brief Returns a reference to the given component for a handle.
     * @tparam Component Type of component to get.
     * @tparam Args Types of arguments to use to construct the component.
     * @param args Parameters to use to initialize the component.
     * @return Reference to the component owned by the handle.
     */
    template<typename Component, typename... Args>
    [[nodiscard]] decltype(auto) get_or_emplace(Args &&...args) const {
        static_assert(((sizeof...(Scope) == 0) || ... || std::is_same_v<Component, Scope>), "Invalid type");
        return reg->template get_or_emplace<Component>(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Returns pointers to the given components for a handle.
     * @tparam Component Types of components to get.
     * @return Pointers to the components owned by the handle.
     */
    template<typename... Component>
    [[nodiscard]] auto try_get() const {
        static_assert(sizeof...(Scope) == 0 || (type_list_contains_v<type_list<Scope...>, Component> && ...), "Invalid type");
        return reg->template try_get<Component...>(entt);
    }

    /**
     * @brief Checks if a handle has components assigned.
     * @return True if the handle has no components assigned, false otherwise.
     */
    [[nodiscard]] bool orphan() const {
        return reg->orphan(entt);
    }

private:
    registry_type *reg;
    entity_type entt;
};

/**
 * @brief Compares two handles.
 * @tparam Args Scope of the first handle.
 * @tparam Other Scope of the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if both handles refer to the same registry and the same
 * entity, false otherwise.
 */
template<typename... Args, typename... Other>
[[nodiscard]] bool operator==(const basic_handle<Args...> &lhs, const basic_handle<Other...> &rhs) noexcept {
    return lhs.registry() == rhs.registry() && lhs.entity() == rhs.entity();
}

/**
 * @brief Compares two handles.
 * @tparam Args Scope of the first handle.
 * @tparam Other Scope of the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return False if both handles refer to the same registry and the same
 * entity, true otherwise.
 */
template<typename... Args, typename... Other>
[[nodiscard]] bool operator!=(const basic_handle<Args...> &lhs, const basic_handle<Other...> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace entt

#endif

// #include "entity/helper.hpp"
#ifndef ENTT_ENTITY_HELPER_HPP
#define ENTT_ENTITY_HELPER_HPP

#include <memory>
#include <type_traits>
// #include "../core/fwd.hpp"

// #include "../core/type_traits.hpp"

// #include "../signal/delegate.hpp"
#ifndef ENTT_SIGNAL_DELEGATE_HPP
#define ENTT_SIGNAL_DELEGATE_HPP

#include <cstddef>
#include <functional>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/type_traits.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Ret, typename... Args>
constexpr auto function_pointer(Ret (*)(Args...)) -> Ret (*)(Args...);

template<typename Ret, typename Type, typename... Args, typename Other>
constexpr auto function_pointer(Ret (*)(Type, Args...), Other &&) -> Ret (*)(Args...);

template<typename Class, typename Ret, typename... Args, typename... Other>
constexpr auto function_pointer(Ret (Class::*)(Args...), Other &&...) -> Ret (*)(Args...);

template<typename Class, typename Ret, typename... Args, typename... Other>
constexpr auto function_pointer(Ret (Class::*)(Args...) const, Other &&...) -> Ret (*)(Args...);

template<typename Class, typename Type, typename... Other>
constexpr auto function_pointer(Type Class::*, Other &&...) -> Type (*)();

template<typename... Type>
using function_pointer_t = decltype(function_pointer(std::declval<Type>()...));

template<typename... Class, typename Ret, typename... Args>
[[nodiscard]] constexpr auto index_sequence_for(Ret (*)(Args...)) {
    return std::index_sequence_for<Class..., Args...>{};
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic delegate implementation.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 */
template<typename>
class delegate;

/**
 * @brief Utility class to use to send around functions and members.
 *
 * Unmanaged delegate for function pointers and members. Users of this class are
 * in charge of disconnecting instances before deleting them.
 *
 * A delegate can be used as a general purpose invoker without memory overhead
 * for free functions possibly with payloads and bound or unbound members.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 */
template<typename Ret, typename... Args>
class delegate<Ret(Args...)> {
    template<auto Candidate, std::size_t... Index>
    [[nodiscard]] auto wrap(std::index_sequence<Index...>) noexcept {
        return [](const void *, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            return static_cast<Ret>(std::invoke(Candidate, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

    template<auto Candidate, typename Type, std::size_t... Index>
    [[nodiscard]] auto wrap(Type &, std::index_sequence<Index...>) noexcept {
        return [](const void *payload, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            return static_cast<Ret>(std::invoke(Candidate, *curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

    template<auto Candidate, typename Type, std::size_t... Index>
    [[nodiscard]] auto wrap(Type *, std::index_sequence<Index...>) noexcept {
        return [](const void *payload, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            return static_cast<Ret>(std::invoke(Candidate, curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

public:
    /*! @brief Function type of the contained target. */
    using function_type = Ret(const void *, Args...);
    /*! @brief Function type of the delegate. */
    using type = Ret(Args...);
    /*! @brief Return type of the delegate. */
    using result_type = Ret;

    /*! @brief Default constructor. */
    delegate() noexcept
        : instance{nullptr},
          fn{nullptr} {}

    /**
     * @brief Constructs a delegate with a given object or payload, if any.
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance Optional valid object that fits the purpose.
     */
    template<auto Candidate, typename... Type>
    delegate(connect_arg_t<Candidate>, Type &&...value_or_instance) noexcept {
        connect<Candidate>(std::forward<Type>(value_or_instance)...);
    }

    /**
     * @brief Constructs a delegate and connects an user defined function with
     * optional payload.
     * @param function Function to connect to the delegate.
     * @param payload User defined arbitrary data.
     */
    delegate(function_type *function, const void *payload = nullptr) noexcept {
        connect(function, payload);
    }

    /**
     * @brief Connects a free function or an unbound member to a delegate.
     * @tparam Candidate Function or member to connect to the delegate.
     */
    template<auto Candidate>
    void connect() noexcept {
        instance = nullptr;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
            fn = [](const void *, Args... args) -> Ret {
                return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
            };
        } else if constexpr(std::is_member_pointer_v<decltype(Candidate)>) {
            fn = wrap<Candidate>(internal::index_sequence_for<type_list_element_t<0, type_list<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
        } else {
            fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
        }
    }

    /**
     * @brief Connects a free function with payload or a bound member to a
     * delegate.
     *
     * The delegate isn't responsible for the connected object or the payload.
     * Users must always guarantee that the lifetime of the instance overcomes
     * the one of the delegate.<br/>
     * When used to connect a free function with payload, its signature must be
     * such that the instance is the first argument before the ones used to
     * define the delegate itself.
     *
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid reference that fits the purpose.
     */
    template<auto Candidate, typename Type>
    void connect(Type &value_or_instance) noexcept {
        instance = &value_or_instance;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type &, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
                return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }

    /**
     * @brief Connects a free function with payload or a bound member to a
     * delegate.
     *
     * @sa connect(Type &)
     *
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid pointer that fits the purpose.
     */
    template<auto Candidate, typename Type>
    void connect(Type *value_or_instance) noexcept {
        instance = value_or_instance;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type *, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
                return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }

    /**
     * @brief Connects an user defined function with optional payload to a
     * delegate.
     *
     * The delegate isn't responsible for the connected object or the payload.
     * Users must always guarantee that the lifetime of an instance overcomes
     * the one of the delegate.<br/>
     * The payload is returned as the first argument to the target function in
     * all cases.
     *
     * @param function Function to connect to the delegate.
     * @param payload User defined arbitrary data.
     */
    void connect(function_type *function, const void *payload = nullptr) noexcept {
        ENTT_ASSERT(function != nullptr, "Uninitialized function pointer");
        instance = payload;
        fn = function;
    }

    /**
     * @brief Resets a delegate.
     *
     * After a reset, a delegate cannot be invoked anymore.
     */
    void reset() noexcept {
        instance = nullptr;
        fn = nullptr;
    }

    /**
     * @brief Returns the instance or the payload linked to a delegate, if any.
     * @return An opaque pointer to the underlying data.
     */
    [[nodiscard]] const void *data() const noexcept {
        return instance;
    }

    /**
     * @brief Triggers a delegate.
     *
     * The delegate invokes the underlying function and returns the result.
     *
     * @warning
     * Attempting to trigger an invalid delegate results in undefined
     * behavior.
     *
     * @param args Arguments to use to invoke the underlying function.
     * @return The value returned by the underlying function.
     */
    Ret operator()(Args... args) const {
        ENTT_ASSERT(static_cast<bool>(*this), "Uninitialized delegate");
        return fn(instance, std::forward<Args>(args)...);
    }

    /**
     * @brief Checks whether a delegate actually stores a listener.
     * @return False if the delegate is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        // no need to also test instance
        return !(fn == nullptr);
    }

    /**
     * @brief Compares the contents of two delegates.
     * @param other Delegate with which to compare.
     * @return False if the two contents differ, true otherwise.
     */
    [[nodiscard]] bool operator==(const delegate<Ret(Args...)> &other) const noexcept {
        return fn == other.fn && instance == other.instance;
    }

private:
    const void *instance;
    function_type *fn;
};

/**
 * @brief Compares the contents of two delegates.
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @param lhs A valid delegate object.
 * @param rhs A valid delegate object.
 * @return True if the two contents differ, false otherwise.
 */
template<typename Ret, typename... Args>
[[nodiscard]] bool operator!=(const delegate<Ret(Args...)> &lhs, const delegate<Ret(Args...)> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Deduction guide.
 * @tparam Candidate Function or member to connect to the delegate.
 */
template<auto Candidate>
delegate(connect_arg_t<Candidate>) -> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;

/**
 * @brief Deduction guide.
 * @tparam Candidate Function or member to connect to the delegate.
 * @tparam Type Type of class or type of payload.
 */
template<auto Candidate, typename Type>
delegate(connect_arg_t<Candidate>, Type &&) -> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;

/**
 * @brief Deduction guide.
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 */
template<typename Ret, typename... Args>
delegate(Ret (*)(const void *, Args...), const void * = nullptr) -> delegate<Ret(Args...)>;

} // namespace entt

#endif

// #include "component.hpp"

// #include "fwd.hpp"

// #include "group.hpp"
#ifndef ENTT_ENTITY_GROUP_HPP
#define ENTT_ENTITY_GROUP_HPP

#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/iterator.hpp"

// #include "../core/type_traits.hpp"

// #include "component.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"

// #include "sparse_set.hpp"

// #include "storage.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename, typename>
class extended_group_iterator;

template<typename It, typename... Owned, typename... Get>
class extended_group_iterator<It, owned_t<Owned...>, get_t<Get...>> {
    template<typename Type>
    auto index_to_element([[maybe_unused]] Type &cpool) const {
        if constexpr(ignore_as_empty_v<typename Type::value_type>) {
            return std::make_tuple();
        } else {
            return std::forward_as_tuple(cpool.rbegin()[it.index()]);
        }
    }

public:
    using difference_type = std::ptrdiff_t;
    using value_type = decltype(std::tuple_cat(std::make_tuple(*std::declval<It>()), std::declval<Owned>().get_as_tuple({})..., std::declval<Get>().get_as_tuple({})...));
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    constexpr extended_group_iterator()
        : it{},
          pools{} {}

    extended_group_iterator(It from, const std::tuple<Owned *..., Get *...> &cpools)
        : it{from},
          pools{cpools} {}

    extended_group_iterator &operator++() noexcept {
        return ++it, *this;
    }

    extended_group_iterator operator++(int) noexcept {
        extended_group_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] reference operator*() const noexcept {
        return std::tuple_cat(std::make_tuple(*it), index_to_element(*std::get<Owned *>(pools))..., std::get<Get *>(pools)->get_as_tuple(*it)...);
    }

    [[nodiscard]] pointer operator->() const noexcept {
        return operator*();
    }

    template<typename... Lhs, typename... Rhs>
    friend constexpr bool operator==(const extended_group_iterator<Lhs...> &, const extended_group_iterator<Rhs...> &) noexcept;

private:
    It it;
    std::tuple<Owned *..., Get *...> pools;
};

template<typename... Lhs, typename... Rhs>
[[nodiscard]] constexpr bool operator==(const extended_group_iterator<Lhs...> &lhs, const extended_group_iterator<Rhs...> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename... Lhs, typename... Rhs>
[[nodiscard]] constexpr bool operator!=(const extended_group_iterator<Lhs...> &lhs, const extended_group_iterator<Rhs...> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Group.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error, but for a few reasonable cases.
 */
template<typename, typename, typename>
class basic_group;

/**
 * @brief Non-owning group.
 *
 * A non-owning group returns all entities and only the entities that are at
 * least in the given storage. Moreover, it's guaranteed that the entity list is
 * tightly packed in memory for fast iterations.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New elements are added to the storage.
 * * The entity currently pointed is modified (for example, components are added
 *   or removed from it).
 * * The entity currently pointed is destroyed.
 *
 * In all other cases, modifying the pools iterated by the group in any way
 * invalidates all the iterators and using them results in undefined behavior.
 *
 * @tparam Get Types of storage _observed_ by the group.
 * @tparam Exclude Types of storage used to filter the group.
 */
template<typename... Get, typename... Exclude>
class basic_group<owned_t<>, get_t<Get...>, exclude_t<Exclude...>> {
    using underlying_type = std::common_type_t<typename Get::entity_type..., typename Exclude::entity_type...>;
    using basic_common_type = std::common_type_t<typename Get::base_type..., typename Exclude::base_type...>;

    template<typename Type>
    static constexpr std::size_t index_of = type_list_index_v<std::remove_const_t<Type>, type_list<typename Get::value_type...>>;

public:
    /*! @brief Underlying entity identifier. */
    using entity_type = underlying_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = basic_common_type;
    /*! @brief Random access iterator type. */
    using iterator = typename base_type::iterator;
    /*! @brief Reversed iterator type. */
    using reverse_iterator = typename base_type::reverse_iterator;
    /*! @brief Iterable group type. */
    using iterable = iterable_adaptor<internal::extended_group_iterator<iterator, owned_t<>, get_t<Get...>>>;

    /*! @brief Default constructor to use to create empty, invalid groups. */
    basic_group() noexcept
        : handler{} {}

    /**
     * @brief Constructs a group from a set of storage classes.
     * @param ref The actual entities to iterate.
     * @param gpool Storage types to iterate _observed_ by the group.
     */
    basic_group(basic_common_type &ref, Get &...gpool) noexcept
        : handler{&ref},
          pools{&gpool...} {}

    /**
     * @brief Returns a const reference to the underlying handler.
     * @return A const reference to the underlying handler.
     */
    [[nodiscard]] const base_type &handle() const noexcept {
        return *handler;
    }

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Type Type of component of which to return the storage.
     * @return The storage for the given component type.
     */
    template<typename Type>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return storage<index_of<Type>>();
    }

    /**
     * @brief Returns the storage for a given index.
     * @tparam Index Index of the storage to return.
     * @return The storage for the given index.
     */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return *std::get<Index>(pools);
    }

    /**
     * @brief Returns the number of entities that are part of the group.
     * @return Number of entities that are part of the group.
     */
    [[nodiscard]] size_type size() const noexcept {
        return *this ? handler->size() : size_type{};
    }

    /**
     * @brief Returns the number of elements that a group has currently
     * allocated space for.
     * @return Capacity of the group.
     */
    [[nodiscard]] size_type capacity() const noexcept {
        return *this ? handler->capacity() : size_type{};
    }

    /*! @brief Requests the removal of unused capacity. */
    void shrink_to_fit() {
        if(*this) {
            handler->shrink_to_fit();
        }
    }

    /**
     * @brief Checks whether a group is empty.
     * @return True if the group is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return !*this || handler->empty();
    }

    /**
     * @brief Returns an iterator to the first entity of the group.
     *
     * The returned iterator points to the first entity of the group. If the
     * group is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the group.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return *this ? handler->begin() : iterator{};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the group.
     *
     * The returned iterator points to the entity following the last entity of
     * the group. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * group.
     */
    [[nodiscard]] iterator end() const noexcept {
        return *this ? handler->end() : iterator{};
    }

    /**
     * @brief Returns an iterator to the first entity of the reversed group.
     *
     * The returned iterator points to the first entity of the reversed group.
     * If the group is empty, the returned iterator will be equal to `rend()`.
     *
     * @return An iterator to the first entity of the reversed group.
     */
    [[nodiscard]] reverse_iterator rbegin() const noexcept {
        return *this ? handler->rbegin() : reverse_iterator{};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the reversed
     * group.
     *
     * The returned iterator points to the entity following the last entity of
     * the reversed group. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * reversed group.
     */
    [[nodiscard]] reverse_iterator rend() const noexcept {
        return *this ? handler->rend() : reverse_iterator{};
    }

    /**
     * @brief Returns the first entity of the group, if any.
     * @return The first entity of the group if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type front() const noexcept {
        const auto it = begin();
        return it != end() ? *it : null;
    }

    /**
     * @brief Returns the last entity of the group, if any.
     * @return The last entity of the group if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type back() const noexcept {
        const auto it = rbegin();
        return it != rend() ? *it : null;
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        const auto it = *this ? handler->find(entt) : iterator{};
        return it != end() && *it == entt ? it : end();
    }

    /**
     * @brief Returns the identifier that occupies the given position.
     * @param pos Position of the element to return.
     * @return The identifier that occupies the given position.
     */
    [[nodiscard]] entity_type operator[](const size_type pos) const {
        return begin()[pos];
    }

    /**
     * @brief Checks if a group is properly initialized.
     * @return True if the group is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return handler != nullptr;
    }

    /**
     * @brief Checks if a group contains an entity.
     * @param entt A valid identifier.
     * @return True if the group contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        return *this && handler->contains(entt);
    }

    /**
     * @brief Returns the components assigned to the given entity.
     *
     * Prefer this function instead of `registry::get` during iterations. It has
     * far better performance than its counterpart.
     *
     * @warning
     * Attempting to use an invalid component type results in a compilation
     * error. Attempting to use an entity that doesn't belong to the group
     * results in undefined behavior.
     *
     * @tparam Type Types of components to get.
     * @param entt A valid identifier.
     * @return The components assigned to the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Type) == 0) {
            return std::apply([entt](auto *...curr) { return std::tuple_cat(curr->get_as_tuple(entt)...); }, pools);
        } else if constexpr(sizeof...(Type) == 1) {
            return (std::get<index_of<Type>>(pools)->get(entt), ...);
        } else {
            return std::tuple_cat(std::get<index_of<Type>>(pools)->get_as_tuple(entt)...);
        }
    }

    /**
     * @brief Iterates entities and components and applies the given function
     * object to them.
     *
     * The function object is invoked for each entity. It is provided with the
     * entity itself and a set of references to non-empty components. The
     * _constness_ of the components is as requested.<br/>
     * The signature of the function must be equivalent to one of the following
     * forms:
     *
     * @code{.cpp}
     * void(const entity_type, Type &...);
     * void(Type &...);
     * @endcode
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        for(const auto entt: *this) {
            if constexpr(is_applicable_v<Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_group>().get({})))>) {
                std::apply(func, std::tuple_cat(std::make_tuple(entt), get(entt)));
            } else {
                std::apply(func, get(entt));
            }
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a group.
     *
     * The iterable object returns tuples that contain the current entity and a
     * set of references to its non-empty components. The _constness_ of the
     * components is as requested.
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @return An iterable object to use to _visit_ the group.
     */
    [[nodiscard]] iterable each() const noexcept {
        return iterable{{begin(), pools}, {end(), pools}};
    }

    /**
     * @brief Sort a group according to the given comparison function.
     *
     * Sort the group so that iterating it with a couple of iterators returns
     * entities and components in the expected order. See `begin` and `end` for
     * more details.
     *
     * The comparison function object must return `true` if the first element
     * is _less_ than the second one, `false` otherwise. The signature of the
     * comparison function should be equivalent to one of the following:
     *
     * @code{.cpp}
     * bool(std::tuple<Type &...>, std::tuple<Type &...>);
     * bool(const Type &..., const Type &...);
     * bool(const Entity, const Entity);
     * @endcode
     *
     * Where `Type` are such that they are iterated by the group.<br/>
     * Moreover, the comparison function object shall induce a
     * _strict weak ordering_ on the values.
     *
     * The sort function object must offer a member function template
     * `operator()` that accepts three arguments:
     *
     * * An iterator to the first element of the range to sort.
     * * An iterator past the last element of the range to sort.
     * * A comparison function to use to compare the elements.
     *
     * @tparam Type Optional types of components to compare.
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename... Type, typename Compare, typename Sort = std_sort, typename... Args>
    void sort(Compare compare, Sort algo = Sort{}, Args &&...args) {
        if(*this) {
            if constexpr(sizeof...(Type) == 0) {
                static_assert(std::is_invocable_v<Compare, const entity_type, const entity_type>, "Invalid comparison function");
                handler->sort(std::move(compare), std::move(algo), std::forward<Args>(args)...);
            } else {
                auto comp = [this, &compare](const entity_type lhs, const entity_type rhs) {
                    if constexpr(sizeof...(Type) == 1) {
                        return compare((std::get<index_of<Type>>(pools)->get(lhs), ...), (std::get<index_of<Type>>(pools)->get(rhs), ...));
                    } else {
                        return compare(std::forward_as_tuple(std::get<index_of<Type>>(pools)->get(lhs)...), std::forward_as_tuple(std::get<index_of<Type>>(pools)->get(rhs)...));
                    }
                };

                handler->sort(std::move(comp), std::move(algo), std::forward<Args>(args)...);
            }
        }
    }

    /**
     * @brief Sort the shared pool of entities according to the given component.
     *
     * Non-owning groups of the same type share with the registry a pool of
     * entities with its own order that doesn't depend on the order of any pool
     * of components. Users can order the underlying data structure so that it
     * respects the order of the pool of the given component.
     *
     * @note
     * The shared pool of entities and thus its order is affected by the changes
     * to each and every pool that it tracks. Therefore changes to those pools
     * can quickly ruin the order imposed to the pool of entities shared between
     * the non-owning groups.
     *
     * @tparam Type Type of component to use to impose the order.
     */
    template<typename Type>
    void sort() const {
        if(*this) {
            handler->respect(*std::get<index_of<Type>>(pools));
        }
    }

private:
    base_type *const handler;
    const std::tuple<Get *...> pools;
};

/**
 * @brief Owning group.
 *
 * Owning groups returns all entities and only the entities that are at
 * least in the given storage. Moreover:
 *
 * * It's guaranteed that the entity list is tightly packed in memory for fast
 *   iterations.
 * * It's guaranteed that all components in the owned storage are tightly packed
 *   in memory for even faster iterations and to allow direct access.
 * * They stay true to the order of the owned storage and all instances have the
 *   same order in memory.
 *
 * The more types of storage are owned, the faster it is to iterate a group.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New elements are added to the storage.
 * * The entity currently pointed is modified (for example, components are added
 *   or removed from it).
 * * The entity currently pointed is destroyed.
 *
 * In all other cases, modifying the pools iterated by the group in any way
 * invalidates all the iterators and using them results in undefined behavior.
 *
 * @tparam Owned Types of storage _owned_ by the group.
 * @tparam Get Types of storage _observed_ by the group.
 * @tparam Exclude Types of storage used to filter the group.
 */
template<typename... Owned, typename... Get, typename... Exclude>
class basic_group<owned_t<Owned...>, get_t<Get...>, exclude_t<Exclude...>> {
    using underlying_type = std::common_type_t<typename Owned::entity_type..., typename Get::entity_type..., typename Exclude::entity_type...>;
    using basic_common_type = std::common_type_t<typename Owned::base_type..., typename Get::base_type..., typename Exclude::base_type...>;

    template<typename Type>
    static constexpr std::size_t index_of = type_list_index_v<std::remove_const_t<Type>, type_list<typename Owned::value_type..., typename Get::value_type...>>;

public:
    /*! @brief Underlying entity identifier. */
    using entity_type = underlying_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = basic_common_type;
    /*! @brief Random access iterator type. */
    using iterator = typename base_type::iterator;
    /*! @brief Reversed iterator type. */
    using reverse_iterator = typename base_type::reverse_iterator;
    /*! @brief Iterable group type. */
    using iterable = iterable_adaptor<internal::extended_group_iterator<iterator, owned_t<Owned...>, get_t<Get...>>>;

    /*! @brief Default constructor to use to create empty, invalid groups. */
    basic_group() noexcept
        : length{} {}

    /**
     * @brief Constructs a group from a set of storage classes.
     * @param extent The actual number of entities to iterate.
     * @param opool Storage types to iterate _owned_ by the group.
     * @param gpool Storage types to iterate _observed_ by the group.
     */
    basic_group(const std::size_t &extent, Owned &...opool, Get &...gpool) noexcept
        : pools{&opool..., &gpool...},
          length{&extent} {}

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Type Type of component of which to return the storage.
     * @return The storage for the given component type.
     */
    template<typename Type>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return storage<index_of<Type>>();
    }

    /**
     * @brief Returns the storage for a given index.
     * @tparam Index Index of the storage to return.
     * @return The storage for the given index.
     */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return *std::get<Index>(pools);
    }

    /**
     * @brief Returns the number of entities that that are part of the group.
     * @return Number of entities that that are part of the group.
     */
    [[nodiscard]] size_type size() const noexcept {
        return *this ? *length : size_type{};
    }

    /**
     * @brief Checks whether a group is empty.
     * @return True if the group is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return !*this || !*length;
    }

    /**
     * @brief Returns an iterator to the first entity of the group.
     *
     * The returned iterator points to the first entity of the group. If the
     * group is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the group.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return *this ? (std::get<0>(pools)->base_type::end() - *length) : iterator{};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the group.
     *
     * The returned iterator points to the entity following the last entity of
     * the group. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * group.
     */
    [[nodiscard]] iterator end() const noexcept {
        return *this ? std::get<0>(pools)->base_type::end() : iterator{};
    }

    /**
     * @brief Returns an iterator to the first entity of the reversed group.
     *
     * The returned iterator points to the first entity of the reversed group.
     * If the group is empty, the returned iterator will be equal to `rend()`.
     *
     * @return An iterator to the first entity of the reversed group.
     */
    [[nodiscard]] reverse_iterator rbegin() const noexcept {
        return *this ? std::get<0>(pools)->base_type::rbegin() : reverse_iterator{};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the reversed
     * group.
     *
     * The returned iterator points to the entity following the last entity of
     * the reversed group. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * reversed group.
     */
    [[nodiscard]] reverse_iterator rend() const noexcept {
        return *this ? (std::get<0>(pools)->base_type::rbegin() + *length) : reverse_iterator{};
    }

    /**
     * @brief Returns the first entity of the group, if any.
     * @return The first entity of the group if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type front() const noexcept {
        const auto it = begin();
        return it != end() ? *it : null;
    }

    /**
     * @brief Returns the last entity of the group, if any.
     * @return The last entity of the group if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type back() const noexcept {
        const auto it = rbegin();
        return it != rend() ? *it : null;
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        const auto it = *this ? std::get<0>(pools)->find(entt) : iterator{};
        return it != end() && it >= begin() && *it == entt ? it : end();
    }

    /**
     * @brief Returns the identifier that occupies the given position.
     * @param pos Position of the element to return.
     * @return The identifier that occupies the given position.
     */
    [[nodiscard]] entity_type operator[](const size_type pos) const {
        return begin()[pos];
    }

    /**
     * @brief Checks if a group is properly initialized.
     * @return True if the group is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return length != nullptr;
    }

    /**
     * @brief Checks if a group contains an entity.
     * @param entt A valid identifier.
     * @return True if the group contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        return *this && std::get<0>(pools)->contains(entt) && (std::get<0>(pools)->index(entt) < (*length));
    }

    /**
     * @brief Returns the components assigned to the given entity.
     *
     * Prefer this function instead of `registry::get` during iterations. It has
     * far better performance than its counterpart.
     *
     * @warning
     * Attempting to use an invalid component type results in a compilation
     * error. Attempting to use an entity that doesn't belong to the group
     * results in undefined behavior.
     *
     * @tparam Type Types of components to get.
     * @param entt A valid identifier.
     * @return The components assigned to the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Type) == 0) {
            return std::apply([entt](auto *...curr) { return std::tuple_cat(curr->get_as_tuple(entt)...); }, pools);
        } else if constexpr(sizeof...(Type) == 1) {
            return (std::get<index_of<Type>>(pools)->get(entt), ...);
        } else {
            return std::tuple_cat(std::get<index_of<Type>>(pools)->get_as_tuple(entt)...);
        }
    }

    /**
     * @brief Iterates entities and components and applies the given function
     * object to them.
     *
     * The function object is invoked for each entity. It is provided with the
     * entity itself and a set of references to non-empty components. The
     * _constness_ of the components is as requested.<br/>
     * The signature of the function must be equivalent to one of the following
     * forms:
     *
     * @code{.cpp}
     * void(const entity_type, Type &...);
     * void(Type &...);
     * @endcode
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        for(auto args: each()) {
            if constexpr(is_applicable_v<Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_group>().get({})))>) {
                std::apply(func, args);
            } else {
                std::apply([&func](auto, auto &&...less) { func(std::forward<decltype(less)>(less)...); }, args);
            }
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a group.
     *
     * The iterable object returns tuples that contain the current entity and a
     * set of references to its non-empty components. The _constness_ of the
     * components is as requested.
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @return An iterable object to use to _visit_ the group.
     */
    [[nodiscard]] iterable each() const noexcept {
        return {{begin(), pools}, {end(), pools}};
    }

    /**
     * @brief Sort a group according to the given comparison function.
     *
     * Sort the group so that iterating it with a couple of iterators returns
     * entities and components in the expected order. See `begin` and `end` for
     * more details.
     *
     * The comparison function object must return `true` if the first element
     * is _less_ than the second one, `false` otherwise. The signature of the
     * comparison function should be equivalent to one of the following:
     *
     * @code{.cpp}
     * bool(std::tuple<Type &...>, std::tuple<Type &...>);
     * bool(const Type &, const Type &);
     * bool(const Entity, const Entity);
     * @endcode
     *
     * Where `Type` are either owned types or not but still such that they are
     * iterated by the group.<br/>
     * Moreover, the comparison function object shall induce a
     * _strict weak ordering_ on the values.
     *
     * The sort function object must offer a member function template
     * `operator()` that accepts three arguments:
     *
     * * An iterator to the first element of the range to sort.
     * * An iterator past the last element of the range to sort.
     * * A comparison function to use to compare the elements.
     *
     * @tparam Type Optional types of components to compare.
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename... Type, typename Compare, typename Sort = std_sort, typename... Args>
    void sort(Compare compare, Sort algo = Sort{}, Args &&...args) const {
        if constexpr(sizeof...(Type) == 0) {
            static_assert(std::is_invocable_v<Compare, const entity_type, const entity_type>, "Invalid comparison function");
            std::get<0>(pools)->sort_n(*length, std::move(compare), std::move(algo), std::forward<Args>(args)...);
        } else {
            auto comp = [this, &compare](const entity_type lhs, const entity_type rhs) {
                if constexpr(sizeof...(Type) == 1) {
                    return compare((std::get<index_of<Type>>(pools)->get(lhs), ...), (std::get<index_of<Type>>(pools)->get(rhs), ...));
                } else {
                    return compare(std::forward_as_tuple(std::get<index_of<Type>>(pools)->get(lhs)...), std::forward_as_tuple(std::get<index_of<Type>>(pools)->get(rhs)...));
                }
            };

            std::get<0>(pools)->sort_n(*length, std::move(comp), std::move(algo), std::forward<Args>(args)...);
        }

        std::apply([this](auto *head, auto *...other) {
            for(auto next = *length; next; --next) {
                const auto pos = next - 1;
                [[maybe_unused]] const auto entt = head->data()[pos];
                (other->swap_elements(other->data()[pos], entt), ...);
            }
        },
                   pools);
    }

private:
    const std::tuple<Owned *..., Get *...> pools;
    const size_type *const length;
};

} // namespace entt

#endif

// #include "view.hpp"
#ifndef ENTT_ENTITY_VIEW_HPP
#define ENTT_ENTITY_VIEW_HPP

#include <array>
#include <iterator>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/iterator.hpp"

// #include "../core/type_traits.hpp"

// #include "component.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"

// #include "sparse_set.hpp"

// #include "storage.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t Get, std::size_t Exclude>
class view_iterator final {
    using iterator_type = typename Type::const_iterator;

    [[nodiscard]] bool valid() const noexcept {
        return ((Get != 0u) || (*it != tombstone))
               && std::apply([entt = *it](const auto *...curr) { return (curr->contains(entt) && ...); }, pools)
               && std::apply([entt = *it](const auto *...curr) { return (!curr->contains(entt) && ...); }, filter);
    }

public:
    using value_type = typename iterator_type::value_type;
    using pointer = typename iterator_type::pointer;
    using reference = typename iterator_type::reference;
    using difference_type = typename iterator_type::difference_type;
    using iterator_category = std::forward_iterator_tag;

    constexpr view_iterator() noexcept
        : it{},
          last{},
          pools{},
          filter{} {}

    view_iterator(iterator_type curr, iterator_type to, std::array<const Type *, Get> all_of, std::array<const Type *, Exclude> none_of) noexcept
        : it{curr},
          last{to},
          pools{all_of},
          filter{none_of} {
        while(it != last && !valid()) {
            ++it;
        }
    }

    view_iterator &operator++() noexcept {
        while(++it != last && !valid()) {}
        return *this;
    }

    view_iterator operator++(int) noexcept {
        view_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] pointer operator->() const noexcept {
        return &*it;
    }

    [[nodiscard]] reference operator*() const noexcept {
        return *operator->();
    }

    template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
    friend constexpr bool operator==(const view_iterator<LhsType, LhsArgs...> &, const view_iterator<RhsType, RhsArgs...> &) noexcept;

private:
    iterator_type it;
    iterator_type last;
    std::array<const Type *, Get> pools;
    std::array<const Type *, Exclude> filter;
};

template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
[[nodiscard]] constexpr bool operator==(const view_iterator<LhsType, LhsArgs...> &lhs, const view_iterator<RhsType, RhsArgs...> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
[[nodiscard]] constexpr bool operator!=(const view_iterator<LhsType, LhsArgs...> &lhs, const view_iterator<RhsType, RhsArgs...> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename It, typename... Type>
struct extended_view_iterator final {
    using difference_type = std::ptrdiff_t;
    using value_type = decltype(std::tuple_cat(std::make_tuple(*std::declval<It>()), std::declval<Type>().get_as_tuple({})...));
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    constexpr extended_view_iterator()
        : it{},
          pools{} {}

    extended_view_iterator(It from, std::tuple<Type *...> storage)
        : it{from},
          pools{storage} {}

    extended_view_iterator &operator++() noexcept {
        return ++it, *this;
    }

    extended_view_iterator operator++(int) noexcept {
        extended_view_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] reference operator*() const noexcept {
        return std::apply([entt = *it](auto *...curr) { return std::tuple_cat(std::make_tuple(entt), curr->get_as_tuple(entt)...); }, pools);
    }

    [[nodiscard]] pointer operator->() const noexcept {
        return operator*();
    }

    template<typename... Lhs, typename... Rhs>
    friend bool constexpr operator==(const extended_view_iterator<Lhs...> &, const extended_view_iterator<Rhs...> &) noexcept;

private:
    It it;
    std::tuple<Type *...> pools;
};

template<typename... Lhs, typename... Rhs>
[[nodiscard]] constexpr bool operator==(const extended_view_iterator<Lhs...> &lhs, const extended_view_iterator<Rhs...> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename... Lhs, typename... Rhs>
[[nodiscard]] constexpr bool operator!=(const extended_view_iterator<Lhs...> &lhs, const extended_view_iterator<Rhs...> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief View implementation.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error, but for a few reasonable cases.
 */
template<typename, typename, typename>
class basic_view;

/**
 * @brief Multi component view.
 *
 * Multi component views iterate over those entities that are at least in the
 * given storage. During initialization, a multi component view looks at the
 * number of entities available for each component and uses the smallest set in
 * order to get a performance boost when iterating.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New elements are added to the storage.
 * * The entity currently pointed is modified (for example, components are added
 *   or removed from it).
 * * The entity currently pointed is destroyed.
 *
 * In all other cases, modifying the pools iterated by the view in any way
 * invalidates all the iterators and using them results in undefined behavior.
 *
 * @tparam Get Types of storage iterated by the view.
 * @tparam Exclude Types of storage used to filter the view.
 */
template<typename... Get, typename... Exclude>
class basic_view<get_t<Get...>, exclude_t<Exclude...>> {
    using underlying_type = std::common_type_t<typename Get::entity_type..., typename Exclude::entity_type...>;
    using basic_common_type = std::common_type_t<typename Get::base_type..., typename Exclude::base_type...>;

    template<typename, typename, typename>
    friend class basic_view;

    template<typename Type>
    static constexpr std::size_t index_of = type_list_index_v<std::remove_const_t<Type>, type_list<typename Get::value_type...>>;

    [[nodiscard]] auto opaque_check_set() const noexcept {
        std::array<const base_type *, sizeof...(Get) - 1u> other{};
        std::apply([&other, pos = 0u, view = view](const auto *...curr) mutable { ((curr == view ? void() : void(other[pos++] = curr)), ...); }, pools);
        return other;
    }

    [[nodiscard]] auto filter_as_array() const noexcept {
        return std::apply([](const auto *...curr) { return std::array<const base_type *, sizeof...(Exclude)>{curr...}; }, filter);
    }

    template<std::size_t Curr, std::size_t Other, typename... Args>
    [[nodiscard]] auto dispatch_get(const std::tuple<underlying_type, Args...> &curr) const {
        if constexpr(Curr == Other) {
            return std::forward_as_tuple(std::get<Args>(curr)...);
        } else {
            return storage<Other>().get_as_tuple(std::get<0>(curr));
        }
    }

    [[nodiscard]] auto reject(const underlying_type entt) const noexcept {
        return std::apply([entt](const auto *...curr) { return (curr->contains(entt) || ...); }, filter);
    }

    template<std::size_t Curr, typename Func, std::size_t... Index>
    void each(Func &func, std::index_sequence<Index...>) const {
        for(const auto curr: storage<Curr>().each()) {
            if(const auto entt = std::get<0>(curr); ((sizeof...(Get) != 1u) || (entt != tombstone)) && ((Curr == Index || storage<Index>().contains(entt)) && ...) && !reject(entt)) {
                if constexpr(is_applicable_v<Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_view>().get({})))>) {
                    std::apply(func, std::tuple_cat(std::make_tuple(entt), dispatch_get<Curr, Index>(curr)...));
                } else {
                    std::apply(func, std::tuple_cat(dispatch_get<Curr, Index>(curr)...));
                }
            }
        }
    }

    template<typename Func, std::size_t... Index>
    void pick_and_each(Func &func, std::index_sequence<Index...> seq) const {
        ((&storage<Index>() == view ? each<Index>(func, seq) : void()), ...);
    }

public:
    /*! @brief Underlying entity identifier. */
    using entity_type = underlying_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = basic_common_type;
    /*! @brief Bidirectional iterator type. */
    using iterator = internal::view_iterator<base_type, sizeof...(Get) - 1u, sizeof...(Exclude)>;
    /*! @brief Iterable view type. */
    using iterable = iterable_adaptor<internal::extended_view_iterator<iterator, Get...>>;

    /*! @brief Default constructor to use to create empty, invalid views. */
    basic_view() noexcept
        : pools{},
          filter{},
          view{} {}

    /**
     * @brief Constructs a multi-type view from a set of storage classes.
     * @param value The storage for the types to iterate.
     * @param exclude The storage for the types used to filter the view.
     */
    basic_view(Get &...value, Exclude &...exclude) noexcept
        : pools{&value...},
          filter{&exclude...},
          view{[](const base_type *first, const auto *...other) { ((first = other->size() < first->size() ? other : first), ...); return first; }(&value...)} {}

    /**
     * @brief Constructs a multi-type view from a set of storage classes.
     * @param value The storage for the types to iterate.
     * @param excl The storage for the types used to filter the view.
     */
    basic_view(std::tuple<Get &...> value, std::tuple<Exclude &...> excl = {}) noexcept
        : pools{std::apply([](auto &...curr) { return std::make_tuple(&curr...); }, value)},
          filter{std::apply([](auto &...curr) { return std::make_tuple(&curr...); }, excl)},
          view{std::apply([](const base_type *first, const auto *...other) { ((first = other->size() < first->size() ? other : first), ...); return first; }, pools)} {}

    /**
     * @brief Creates a new view driven by a given component in its iterations.
     * @tparam Type Type of component used to drive the iteration.
     * @return A new view driven by the given component in its iterations.
     */
    template<typename Type>
    [[nodiscard]] basic_view use() const noexcept {
        return use<index_of<Type>>();
    }

    /**
     * @brief Creates a new view driven by a given component in its iterations.
     * @tparam Index Index of the component used to drive the iteration.
     * @return A new view driven by the given component in its iterations.
     */
    template<std::size_t Index>
    [[nodiscard]] basic_view use() const noexcept {
        basic_view other{*this};
        other.view = &storage<Index>();
        return other;
    }

    /**
     * @brief Updates the internal leading view if required.
     * @return A newly created and internally optimized view.
     */
    [[nodiscard]] basic_view refresh() const noexcept {
        return std::apply([](auto *...elem) { return basic_view{*elem...}; }, std::tuple_cat(pools, filter));
    }

    /**
     * @brief Returns the leading storage of a view.
     * @return The leading storage of the view.
     */
    [[nodiscard]] const base_type &handle() const noexcept {
        return *view;
    }

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Comp Type of component of which to return the storage.
     * @return The storage for the given component type.
     */
    template<typename Type>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return storage<index_of<Type>>();
    }

    /**
     * @brief Returns the storage for a given index.
     * @tparam Index Index of the storage to return.
     * @return The storage for the given index.
     */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return *std::get<Index>(pools);
    }

    /**
     * @brief Estimates the number of entities iterated by the view.
     * @return Estimated number of entities iterated by the view.
     */
    [[nodiscard]] size_type size_hint() const noexcept {
        return view->size();
    }

    /**
     * @brief Returns an iterator to the first entity of the view.
     *
     * The returned iterator points to the first entity of the view. If the view
     * is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the view.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return iterator{view->begin(), view->end(), opaque_check_set(), filter_as_array()};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the view.
     *
     * The returned iterator points to the entity following the last entity of
     * the view. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the view.
     */
    [[nodiscard]] iterator end() const noexcept {
        return iterator{view->end(), view->end(), opaque_check_set(), filter_as_array()};
    }

    /**
     * @brief Returns the first entity of the view, if any.
     * @return The first entity of the view if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type front() const noexcept {
        const auto it = begin();
        return it != end() ? *it : null;
    }

    /**
     * @brief Returns the last entity of the view, if any.
     * @return The last entity of the view if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type back() const noexcept {
        auto it = view->rbegin();
        for(const auto last = view->rend(); it != last && !contains(*it); ++it) {}
        return it == view->rend() ? null : *it;
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        return contains(entt) ? iterator{view->find(entt), view->end(), opaque_check_set(), filter_as_array()} : end();
    }

    /**
     * @brief Returns the components assigned to the given entity.
     * @param entt A valid identifier.
     * @return The components assigned to the given entity.
     */
    [[nodiscard]] decltype(auto) operator[](const entity_type entt) const {
        return get(entt);
    }

    /**
     * @brief Checks if a view is properly initialized.
     * @return True if the view is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return view != nullptr;
    }

    /**
     * @brief Checks if a view contains an entity.
     * @param entt A valid identifier.
     * @return True if the view contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        return std::apply([entt](const auto *...curr) { return (curr->contains(entt) && ...); }, pools)
               && std::apply([entt](const auto *...curr) { return (!curr->contains(entt) && ...); }, filter);
    }

    /**
     * @brief Returns the components assigned to the given entity.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the view results in
     * undefined behavior.
     *
     * @tparam Type Types of components to get.
     * @param entt A valid identifier.
     * @return The components assigned to the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Type) == 0) {
            return std::apply([entt](auto *...curr) { return std::tuple_cat(curr->get_as_tuple(entt)...); }, pools);
        } else if constexpr(sizeof...(Type) == 1) {
            return (storage<index_of<Type>>().get(entt), ...);
        } else {
            return std::tuple_cat(storage<index_of<Type>>().get_as_tuple(entt)...);
        }
    }

    /**
     * @brief Returns the components assigned to the given entity.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the view results in
     * undefined behavior.
     *
     * @tparam First Index of a component to get.
     * @tparam Other Indexes of other components to get.
     * @param entt A valid identifier.
     * @return The components assigned to the entity.
     */
    template<std::size_t First, std::size_t... Other>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Other) == 0) {
            return storage<First>().get(entt);
        } else {
            return std::tuple_cat(storage<First>().get_as_tuple(entt), storage<Other>().get_as_tuple(entt)...);
        }
    }

    /**
     * @brief Iterates entities and components and applies the given function
     * object to them.
     *
     * The function object is invoked for each entity. It is provided with the
     * entity itself and a set of references to non-empty components. The
     * _constness_ of the components is as requested.<br/>
     * The signature of the function must be equivalent to one of the following
     * forms:
     *
     * @code{.cpp}
     * void(const entity_type, Type &...);
     * void(Type &...);
     * @endcode
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        pick_and_each(func, std::index_sequence_for<Get...>{});
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a view.
     *
     * The iterable object returns a tuple that contains the current entity and
     * a set of references to its non-empty components. The _constness_ of the
     * components is as requested.
     *
     * @return An iterable object to use to _visit_ the view.
     */
    [[nodiscard]] iterable each() const noexcept {
        return {internal::extended_view_iterator{begin(), pools}, internal::extended_view_iterator{end(), pools}};
    }

    /**
     * @brief Combines two views in a _more specific_ one (friend function).
     * @tparam OGet Component list of the view to combine with.
     * @tparam OExclude Filter list of the view to combine with.
     * @param other The view to combine with.
     * @return A more specific view.
     */
    template<typename... OGet, typename... OExclude>
    [[nodiscard]] auto operator|(const basic_view<get_t<OGet...>, exclude_t<OExclude...>> &other) const noexcept {
        return std::make_from_tuple<basic_view<get_t<Get..., OGet...>, exclude_t<Exclude..., OExclude...>>>(
            std::apply([](auto *...curr) { return std::forward_as_tuple(*curr...); }, std::tuple_cat(pools, other.pools, filter, other.filter)));
    }

private:
    std::tuple<Get *...> pools;
    std::tuple<Exclude *...> filter;
    const base_type *view;
};

/**
 * @brief Single component view specialization.
 *
 * Single component views are specialized in order to get a boost in terms of
 * performance. This kind of views can access the underlying data structure
 * directly and avoid superfluous checks.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New elements are added to the storage.
 * * The entity currently pointed is modified (for example, components are added
 *   or removed from it).
 * * The entity currently pointed is destroyed.
 *
 * In all other cases, modifying the pool iterated by the view in any way
 * invalidates all the iterators and using them results in undefined behavior.
 *
 * @tparam Get Type of storage iterated by the view.
 */
template<typename Get>
class basic_view<get_t<Get>, exclude_t<>, std::void_t<std::enable_if_t<!component_traits<typename Get::value_type>::in_place_delete>>> {
    template<typename, typename, typename>
    friend class basic_view;

public:
    /*! @brief Underlying entity identifier. */
    using entity_type = typename Get::entity_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = typename Get::base_type;
    /*! @brief Random access iterator type. */
    using iterator = typename base_type::iterator;
    /*! @brief Reversed iterator type. */
    using reverse_iterator = typename base_type::reverse_iterator;
    /*! @brief Iterable view type. */
    using iterable = decltype(std::declval<Get>().each());

    /*! @brief Default constructor to use to create empty, invalid views. */
    basic_view() noexcept
        : pools{},
          filter{} {}

    /**
     * @brief Constructs a single-type view from a storage class.
     * @param ref The storage for the type to iterate.
     */
    basic_view(Get &ref) noexcept
        : pools{&ref},
          filter{} {}

    /**
     * @brief Constructs a single-type view from a storage class.
     * @param ref The storage for the type to iterate.
     */
    basic_view(std::tuple<Get &> ref, std::tuple<> = {}) noexcept
        : pools{&std::get<0>(ref)},
          filter{} {}

    /**
     * @brief Returns the leading storage of a view.
     * @return The leading storage of the view.
     */
    [[nodiscard]] const base_type &handle() const noexcept {
        return storage();
    }

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Type Type of component of which to return the storage.
     * @return The storage for the given component type.
     */
    template<typename Type = typename Get::value_type>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        static_assert(std::is_same_v<std::remove_const_t<Type>, typename Get::value_type>, "Invalid component type");
        return storage<0>();
    }

    /**
     * @brief Returns the storage for a given index.
     * @tparam Index Index of the storage to return.
     * @return The storage for the given index.
     */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return *std::get<Index>(pools);
    }

    /**
     * @brief Returns the number of entities that have the given component.
     * @return Number of entities that have the given component.
     */
    [[nodiscard]] size_type size() const noexcept {
        return handle().size();
    }

    /**
     * @brief Checks whether a view is empty.
     * @return True if the view is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return handle().empty();
    }

    /**
     * @brief Returns an iterator to the first entity of the view.
     *
     * The returned iterator points to the first entity of the view. If the view
     * is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the view.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return handle().begin();
    }

    /**
     * @brief Returns an iterator that is past the last entity of the view.
     *
     * The returned iterator points to the entity following the last entity of
     * the view. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the view.
     */
    [[nodiscard]] iterator end() const noexcept {
        return handle().end();
    }

    /**
     * @brief Returns an iterator to the first entity of the reversed view.
     *
     * The returned iterator points to the first entity of the reversed view. If
     * the view is empty, the returned iterator will be equal to `rend()`.
     *
     * @return An iterator to the first entity of the reversed view.
     */
    [[nodiscard]] reverse_iterator rbegin() const noexcept {
        return handle().rbegin();
    }

    /**
     * @brief Returns an iterator that is past the last entity of the reversed
     * view.
     *
     * The returned iterator points to the entity following the last entity of
     * the reversed view. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * reversed view.
     */
    [[nodiscard]] reverse_iterator rend() const noexcept {
        return handle().rend();
    }

    /**
     * @brief Returns the first entity of the view, if any.
     * @return The first entity of the view if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type front() const noexcept {
        return empty() ? null : *begin();
    }

    /**
     * @brief Returns the last entity of the view, if any.
     * @return The last entity of the view if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type back() const noexcept {
        return empty() ? null : *rbegin();
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        return contains(entt) ? handle().find(entt) : end();
    }

    /**
     * @brief Returns the identifier that occupies the given position.
     * @param pos Position of the element to return.
     * @return The identifier that occupies the given position.
     */
    [[nodiscard]] entity_type operator[](const size_type pos) const {
        return begin()[pos];
    }

    /**
     * @brief Returns the component assigned to the given entity.
     * @param entt A valid identifier.
     * @return The component assigned to the given entity.
     */
    [[nodiscard]] decltype(auto) operator[](const entity_type entt) const {
        return storage().get(entt);
    }

    /**
     * @brief Checks if a view is properly initialized.
     * @return True if the view is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return std::get<0>(pools) != nullptr;
    }

    /**
     * @brief Checks if a view contains an entity.
     * @param entt A valid identifier.
     * @return True if the view contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        return handle().contains(entt);
    }

    /**
     * @brief Returns the component assigned to the given entity.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the view results in
     * undefined behavior.
     *
     * @tparam Type Type or index of the component to get.
     * @param entt A valid identifier.
     * @return The component assigned to the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Type) == 0) {
            return storage().get_as_tuple(entt);
        } else {
            static_assert((std::is_same_v<std::remove_const_t<Type>, typename Get::value_type> && ...), "Invalid component type");
            return storage().get(entt);
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        return storage().get(entt);
    }

    /**
     * @brief Iterates entities and components and applies the given function
     * object to them.
     *
     * The function object is invoked for each entity. It is provided with the
     * entity itself and a reference to the component if it's a non-empty one.
     * The _constness_ of the component is as requested.<br/>
     * The signature of the function must be equivalent to one of the following
     * forms:
     *
     * @code{.cpp}
     * void(const entity_type, Type &);
     * void(typename Type &);
     * @endcode
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        if constexpr(is_applicable_v<Func, decltype(*each().begin())>) {
            for(const auto pack: each()) {
                std::apply(func, pack);
            }
        } else if constexpr(ignore_as_empty_v<typename Get::value_type>) {
            for(size_type pos{}, last = size(); pos < last; ++pos) {
                func();
            }
        } else {
            for(auto &&component: storage()) {
                func(component);
            }
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a view.
     *
     * The iterable object returns a tuple that contains the current entity and
     * a reference to its component if it's a non-empty one. The _constness_ of
     * the component is as requested.
     *
     * @return An iterable object to use to _visit_ the view.
     */
    [[nodiscard]] iterable each() const noexcept {
        return storage().each();
    }

    /**
     * @brief Combines two views in a _more specific_ one (friend function).
     * @tparam OGet Component list of the view to combine with.
     * @tparam OExclude Filter list of the view to combine with.
     * @param other The view to combine with.
     * @return A more specific view.
     */
    template<typename... OGet, typename... OExclude>
    [[nodiscard]] auto operator|(const basic_view<get_t<OGet...>, exclude_t<OExclude...>> &other) const noexcept {
        return std::make_from_tuple<basic_view<get_t<Get, OGet...>, exclude_t<OExclude...>>>(
            std::apply([](auto *...curr) { return std::forward_as_tuple(*curr...); }, std::tuple_cat(pools, other.pools, other.filter)));
    }

private:
    std::tuple<Get *> pools;
    std::tuple<> filter;
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of storage classes used to create the view.
 * @param storage The storage for the types to iterate.
 */
template<typename... Type>
basic_view(Type &...storage) -> basic_view<get_t<Type...>, exclude_t<>>;

/**
 * @brief Deduction guide.
 * @tparam Get Types of components iterated by the view.
 * @tparam Exclude Types of components used to filter the view.
 */
template<typename... Get, typename... Exclude>
basic_view(std::tuple<Get &...>, std::tuple<Exclude &...> = {}) -> basic_view<get_t<Get...>, exclude_t<Exclude...>>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Converts a registry to a view.
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class as_view {
    template<typename... Get, typename... Exclude>
    auto dispatch(get_t<Get...>, exclude_t<Exclude...>) const {
        return reg.template view<constness_as_t<typename Get::value_type, Get>...>(exclude_t<constness_as_t<typename Exclude::value_type, Exclude>...>{});
    }

public:
    /*! @brief Type of registry to convert. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = std::remove_const_t<typename registry_type::entity_type>;

    /**
     * @brief Constructs a converter for a given registry.
     * @param source A valid reference to a registry.
     */
    as_view(registry_type &source) noexcept
        : reg{source} {}

    /**
     * @brief Conversion function from a registry to a view.
     * @tparam Get Type of storage used to construct the view.
     * @tparam Exclude Types of storage used to filter the view.
     * @return A newly created view.
     */
    template<typename Get, typename Exclude>
    operator basic_view<Get, Exclude>() const {
        return dispatch(Get{}, Exclude{});
    }

private:
    registry_type &reg;
};

/**
 * @brief Converts a registry to a group.
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class as_group {
    template<typename... Owned, typename... Get, typename... Exclude>
    auto dispatch(owned_t<Owned...>, get_t<Get...>, exclude_t<Exclude...>) const {
        if constexpr(std::is_const_v<registry_type>) {
            return reg.template group_if_exists<typename Owned::value_type...>(get_t<typename Get::value_type...>{}, exclude_t<typename Exclude::value_type...>{});
        } else {
            return reg.template group<constness_as_t<typename Owned::value_type, Owned>...>(get_t<constness_as_t<typename Get::value_type, Get>...>{}, exclude_t<constness_as_t<typename Exclude::value_type, Exclude>...>{});
        }
    }

public:
    /*! @brief Type of registry to convert. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = std::remove_const_t<typename registry_type::entity_type>;

    /**
     * @brief Constructs a converter for a given registry.
     * @param source A valid reference to a registry.
     */
    as_group(registry_type &source) noexcept
        : reg{source} {}

    /**
     * @brief Conversion function from a registry to a group.
     * @tparam Owned Types of _owned_ by the group.
     * @tparam Get Types of storage _observed_ by the group.
     * @tparam Exclude Types of storage used to filter the group.
     * @return A newly created group.
     */
    template<typename Owned, typename Get, typename Exclude>
    operator basic_group<Owned, Get, Exclude>() const {
        return dispatch(Owned{}, Get{}, Exclude{});
    }

private:
    registry_type &reg;
};

/**
 * @brief Helper to create a listener that directly invokes a member function.
 * @tparam Member Member function to invoke on a component of the given type.
 * @tparam Registry Basic registry type.
 * @param reg A registry that contains the given entity and its components.
 * @param entt Entity from which to get the component.
 */
template<auto Member, typename Registry = std::decay_t<nth_argument_t<0u, Member>>>
void invoke(Registry &reg, const typename Registry::entity_type entt) {
    static_assert(std::is_member_function_pointer_v<decltype(Member)>, "Invalid pointer to non-static member function");
    delegate<void(Registry &, const typename Registry::entity_type)> func;
    func.template connect<Member>(reg.template get<member_class_t<decltype(Member)>>(entt));
    func(reg, entt);
}

/**
 * @brief Returns the entity associated with a given component.
 *
 * @warning
 * Currently, this function only works correctly with the default pool as it
 * makes assumptions about how the components are laid out.
 *
 * @tparam Registry Basic registry type.
 * @tparam Component Type of component.
 * @param reg A registry that contains the given entity and its components.
 * @param instance A valid component instance.
 * @return The entity associated with the given component.
 */
template<typename Registry, typename Component>
typename Registry::entity_type to_entity(const Registry &reg, const Component &instance) {
    const auto &storage = reg.template storage<Component>();
    const typename Registry::base_type &base = storage;
    const auto *addr = std::addressof(instance);

    for(auto it = base.rbegin(), last = base.rend(); it < last; it += component_traits<Component>::page_size) {
        if(const auto dist = (addr - std::addressof(storage.get(*it))); dist >= 0 && dist < static_cast<decltype(dist)>(component_traits<Component>::page_size)) {
            return *(it + dist);
        }
    }

    return null;
}

} // namespace entt

#endif

// #include "entity/observer.hpp"
#ifndef ENTT_ENTITY_OBSERVER_HPP
#define ENTT_ENTITY_OBSERVER_HPP

#include <cstddef>
#include <cstdint>
#include <limits>
#include <type_traits>
#include <utility>
// #include "../core/type_traits.hpp"

// #include "../signal/delegate.hpp"

// #include "fwd.hpp"

// #include "storage.hpp"


namespace entt {

/*! @brief Grouping matcher. */
template<typename...>
struct matcher {};

/**
 * @brief Collector.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error, but for a few reasonable cases.
 */
template<typename...>
struct basic_collector;

/**
 * @brief Collector.
 *
 * A collector contains a set of rules (literally, matchers) to use to track
 * entities.<br/>
 * Its main purpose is to generate a descriptor that allows an observer to know
 * how to connect to a registry.
 */
template<>
struct basic_collector<> {
    /**
     * @brief Adds a grouping matcher to the collector.
     * @tparam AllOf Types of components tracked by the matcher.
     * @tparam NoneOf Types of components used to filter out entities.
     * @return The updated collector.
     */
    template<typename... AllOf, typename... NoneOf>
    static constexpr auto group(exclude_t<NoneOf...> = {}) noexcept {
        return basic_collector<matcher<type_list<>, type_list<>, type_list<NoneOf...>, AllOf...>>{};
    }

    /**
     * @brief Adds an observing matcher to the collector.
     * @tparam AnyOf Type of component for which changes should be detected.
     * @return The updated collector.
     */
    template<typename AnyOf>
    static constexpr auto update() noexcept {
        return basic_collector<matcher<type_list<>, type_list<>, AnyOf>>{};
    }
};

/**
 * @brief Collector.
 * @copydetails basic_collector<>
 * @tparam Reject Untracked types used to filter out entities.
 * @tparam Require Untracked types required by the matcher.
 * @tparam Rule Specific details of the current matcher.
 * @tparam Other Other matchers.
 */
template<typename... Reject, typename... Require, typename... Rule, typename... Other>
struct basic_collector<matcher<type_list<Reject...>, type_list<Require...>, Rule...>, Other...> {
    /*! @brief Current matcher. */
    using current_type = matcher<type_list<Reject...>, type_list<Require...>, Rule...>;

    /**
     * @brief Adds a grouping matcher to the collector.
     * @tparam AllOf Types of components tracked by the matcher.
     * @tparam NoneOf Types of components used to filter out entities.
     * @return The updated collector.
     */
    template<typename... AllOf, typename... NoneOf>
    static constexpr auto group(exclude_t<NoneOf...> = {}) noexcept {
        return basic_collector<matcher<type_list<>, type_list<>, type_list<NoneOf...>, AllOf...>, current_type, Other...>{};
    }

    /**
     * @brief Adds an observing matcher to the collector.
     * @tparam AnyOf Type of component for which changes should be detected.
     * @return The updated collector.
     */
    template<typename AnyOf>
    static constexpr auto update() noexcept {
        return basic_collector<matcher<type_list<>, type_list<>, AnyOf>, current_type, Other...>{};
    }

    /**
     * @brief Updates the filter of the last added matcher.
     * @tparam AllOf Types of components required by the matcher.
     * @tparam NoneOf Types of components used to filter out entities.
     * @return The updated collector.
     */
    template<typename... AllOf, typename... NoneOf>
    static constexpr auto where(exclude_t<NoneOf...> = {}) noexcept {
        using extended_type = matcher<type_list<Reject..., NoneOf...>, type_list<Require..., AllOf...>, Rule...>;
        return basic_collector<extended_type, Other...>{};
    }
};

/*! @brief Variable template used to ease the definition of collectors. */
inline constexpr basic_collector<> collector{};

/**
 * @brief Observer.
 *
 * An observer returns all the entities and only the entities that fit the
 * requirements of at least one matcher. Moreover, it's guaranteed that the
 * entity list is tightly packed in memory for fast iterations.<br/>
 * In general, observers don't stay true to the order of any set of components.
 *
 * Observers work mainly with two types of matchers, provided through a
 * collector:
 *
 * * Observing matcher: an observer will return at least all the living entities
 *   for which one or more of the given components have been updated and not yet
 *   destroyed.
 * * Grouping matcher: an observer will return at least all the living entities
 *   that would have entered the given group if it existed and that would have
 *   not yet left it.
 *
 * If an entity respects the requirements of multiple matchers, it will be
 * returned once and only once by the observer in any case.
 *
 * Matchers support also filtering by means of a _where_ clause that accepts
 * both a list of types and an exclusion list.<br/>
 * Whenever a matcher finds that an entity matches its requirements, the
 * condition of the filter is verified before to register the entity itself.
 * Moreover, a registered entity isn't returned by the observer if the condition
 * set by the filter is broken in the meantime.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New instances of the given components are created and assigned to entities.
 * * The entity currently pointed is modified (as an example, if one of the
 *   given components is removed from the entity to which the iterator points).
 * * The entity currently pointed is destroyed.
 *
 * In all the other cases, modifying the pools of the given components in any
 * way invalidates all the iterators and using them results in undefined
 * behavior.
 *
 * @warning
 * Lifetime of an observer doesn't necessarily have to overcome that of the
 * registry to which it is connected. However, the observer must be disconnected
 * from the registry before being destroyed to avoid crashes due to dangling
 * pointers.
 *
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class basic_observer: private basic_storage<std::uint32_t, typename Registry::entity_type> {
    using base_type = basic_storage<std::uint32_t, typename Registry::entity_type>;

    template<typename>
    struct matcher_handler;

    template<typename... Reject, typename... Require, typename AnyOf>
    struct matcher_handler<matcher<type_list<Reject...>, type_list<Require...>, AnyOf>> {
        template<std::size_t Index>
        static void maybe_valid_if(basic_observer &obs, Registry &reg, const typename Registry::entity_type entt) {
            if(reg.template all_of<Require...>(entt) && !reg.template any_of<Reject...>(entt)) {
                if(!obs.contains(entt)) {
                    obs.emplace(entt);
                }

                obs.get(entt) |= (1 << Index);
            }
        }

        template<std::size_t Index>
        static void discard_if(basic_observer &obs, Registry &, const typename Registry::entity_type entt) {
            if(obs.contains(entt) && !(obs.get(entt) &= (~(1 << Index)))) {
                obs.erase(entt);
            }
        }

        template<std::size_t Index>
        static void connect(basic_observer &obs, Registry &reg) {
            (reg.template on_destroy<Require>().template connect<&discard_if<Index>>(obs), ...);
            (reg.template on_construct<Reject>().template connect<&discard_if<Index>>(obs), ...);
            reg.template on_update<AnyOf>().template connect<&maybe_valid_if<Index>>(obs);
            reg.template on_destroy<AnyOf>().template connect<&discard_if<Index>>(obs);
        }

        static void disconnect(basic_observer &obs, Registry &reg) {
            (reg.template on_destroy<Require>().disconnect(obs), ...);
            (reg.template on_construct<Reject>().disconnect(obs), ...);
            reg.template on_update<AnyOf>().disconnect(obs);
            reg.template on_destroy<AnyOf>().disconnect(obs);
        }
    };

    template<typename... Reject, typename... Require, typename... NoneOf, typename... AllOf>
    struct matcher_handler<matcher<type_list<Reject...>, type_list<Require...>, type_list<NoneOf...>, AllOf...>> {
        template<std::size_t Index, typename... Ignore>
        static void maybe_valid_if(basic_observer &obs, Registry &reg, const typename Registry::entity_type entt) {
            auto condition = [&reg, entt]() {
                if constexpr(sizeof...(Ignore) == 0) {
                    return reg.template all_of<AllOf..., Require...>(entt) && !reg.template any_of<NoneOf..., Reject...>(entt);
                } else {
                    return reg.template all_of<AllOf..., Require...>(entt) && ((std::is_same_v<Ignore..., NoneOf> || !reg.template any_of<NoneOf>(entt)) && ...) && !reg.template any_of<Reject...>(entt);
                }
            };

            if(condition()) {
                if(!obs.contains(entt)) {
                    obs.emplace(entt);
                }

                obs.get(entt) |= (1 << Index);
            }
        }

        template<std::size_t Index>
        static void discard_if(basic_observer &obs, Registry &, const typename Registry::entity_type entt) {
            if(obs.contains(entt) && !(obs.get(entt) &= (~(1 << Index)))) {
                obs.erase(entt);
            }
        }

        template<std::size_t Index>
        static void connect(basic_observer &obs, Registry &reg) {
            (reg.template on_destroy<Require>().template connect<&discard_if<Index>>(obs), ...);
            (reg.template on_construct<Reject>().template connect<&discard_if<Index>>(obs), ...);
            (reg.template on_construct<AllOf>().template connect<&maybe_valid_if<Index>>(obs), ...);
            (reg.template on_destroy<NoneOf>().template connect<&maybe_valid_if<Index, NoneOf>>(obs), ...);
            (reg.template on_destroy<AllOf>().template connect<&discard_if<Index>>(obs), ...);
            (reg.template on_construct<NoneOf>().template connect<&discard_if<Index>>(obs), ...);
        }

        static void disconnect(basic_observer &obs, Registry &reg) {
            (reg.template on_destroy<Require>().disconnect(obs), ...);
            (reg.template on_construct<Reject>().disconnect(obs), ...);
            (reg.template on_construct<AllOf>().disconnect(obs), ...);
            (reg.template on_destroy<NoneOf>().disconnect(obs), ...);
            (reg.template on_destroy<AllOf>().disconnect(obs), ...);
            (reg.template on_construct<NoneOf>().disconnect(obs), ...);
        }
    };

    template<typename... Matcher>
    static void disconnect(Registry &reg, basic_observer &obs) {
        (matcher_handler<Matcher>::disconnect(obs, reg), ...);
    }

    template<typename... Matcher, std::size_t... Index>
    void connect(Registry &reg, std::index_sequence<Index...>) {
        static_assert(sizeof...(Matcher) < std::numeric_limits<typename base_type::value_type>::digits, "Too many matchers");
        (matcher_handler<Matcher>::template connect<Index>(*this, reg), ...);
        release.template connect<&basic_observer::disconnect<Matcher...>>(reg);
    }

public:
    /*! Basic registry type. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename registry_type::entity_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Random access iterator type. */
    using iterator = typename registry_type::base_type::iterator;

    /*! @brief Default constructor. */
    basic_observer()
        : release{} {}

    /*! @brief Default copy constructor, deleted on purpose. */
    basic_observer(const basic_observer &) = delete;
    /*! @brief Default move constructor, deleted on purpose. */
    basic_observer(basic_observer &&) = delete;

    /**
     * @brief Creates an observer and connects it to a given registry.
     * @tparam Matcher Types of matchers to use to initialize the observer.
     * @param reg A valid reference to a registry.
     */
    template<typename... Matcher>
    basic_observer(registry_type &reg, basic_collector<Matcher...>)
        : basic_observer{} {
        connect<Matcher...>(reg, std::index_sequence_for<Matcher...>{});
    }

    /*! @brief Default destructor. */
    ~basic_observer() = default;

    /**
     * @brief Default copy assignment operator, deleted on purpose.
     * @return This observer.
     */
    basic_observer &operator=(const basic_observer &) = delete;

    /**
     * @brief Default move assignment operator, deleted on purpose.
     * @return This observer.
     */
    basic_observer &operator=(basic_observer &&) = delete;

    /**
     * @brief Connects an observer to a given registry.
     * @tparam Matcher Types of matchers to use to initialize the observer.
     * @param reg A valid reference to a registry.
     */
    template<typename... Matcher>
    void connect(registry_type &reg, basic_collector<Matcher...>) {
        disconnect();
        connect<Matcher...>(reg, std::index_sequence_for<Matcher...>{});
        base_type::clear();
    }

    /*! @brief Disconnects an observer from the registry it keeps track of. */
    void disconnect() {
        if(release) {
            release(*this);
            release.reset();
        }
    }

    /**
     * @brief Returns the number of elements in an observer.
     * @return Number of elements.
     */
    [[nodiscard]] size_type size() const noexcept {
        return base_type::size();
    }

    /**
     * @brief Checks whether an observer is empty.
     * @return True if the observer is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return base_type::empty();
    }

    /**
     * @brief Direct access to the list of entities of the observer.
     *
     * The returned pointer is such that range `[data(), data() + size())` is
     * always a valid range, even if the container is empty.
     *
     * @note
     * Entities are in the reverse order as returned by the `begin`/`end`
     * iterators.
     *
     * @return A pointer to the array of entities.
     */
    [[nodiscard]] const entity_type *data() const noexcept {
        return base_type::data();
    }

    /**
     * @brief Returns an iterator to the first entity of the observer.
     *
     * The returned iterator points to the first entity of the observer. If the
     * container is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the observer.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return base_type::base_type::begin();
    }

    /**
     * @brief Returns an iterator that is past the last entity of the observer.
     *
     * The returned iterator points to the entity following the last entity of
     * the observer. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * observer.
     */
    [[nodiscard]] iterator end() const noexcept {
        return base_type::base_type::end();
    }

    /*! @brief Clears the underlying container. */
    void clear() noexcept {
        base_type::clear();
    }

    /**
     * @brief Iterates entities and applies the given function object to them.
     *
     * The function object is invoked for each entity.<br/>
     * The signature of the function must be equivalent to the following form:
     *
     * @code{.cpp}
     * void(const entity_type);
     * @endcode
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        for(const auto entity: *this) {
            func(entity);
        }
    }

    /**
     * @brief Iterates entities and applies the given function object to them,
     * then clears the observer.
     *
     * @sa each
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) {
        std::as_const(*this).each(std::move(func));
        clear();
    }

private:
    delegate<void(basic_observer &)> release;
};

} // namespace entt

#endif

// #include "entity/organizer.hpp"
#ifndef ENTT_ENTITY_ORGANIZER_HPP
#define ENTT_ENTITY_ORGANIZER_HPP

#include <cstddef>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../core/type_info.hpp"

// #include "../core/type_traits.hpp"

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "../graph/adjacency_matrix.hpp"
#ifndef ENTT_GRAPH_ADJACENCY_MATRIX_HPP
#define ENTT_GRAPH_ADJACENCY_MATRIX_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_GRAPH_FWD_HPP
#define ENTT_GRAPH_FWD_HPP

#include <cstddef>
#include <memory>
// #include "../core/fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/*! @brief Undirected graph category tag. */
struct directed_tag {};

/*! @brief Directed graph category tag. */
struct undirected_tag: directed_tag {};

template<typename, typename = std::allocator<std::size_t>>
class adjacency_matrix;

template<typename = std::allocator<id_type>>
class basic_flow;

/*! @brief Alias declaration for the most common use case. */
using flow = basic_flow<>;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class edge_iterator {
    using size_type = std::size_t;

public:
    using value_type = std::pair<size_type, size_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr edge_iterator() noexcept
        : it{},
          vert{},
          pos{},
          last{},
          offset{} {}

    constexpr edge_iterator(It base, const size_type vertices, const size_type from, const size_type to, const size_type step) noexcept
        : it{std::move(base)},
          vert{vertices},
          pos{from},
          last{to},
          offset{step} {
        for(; pos != last && !it[pos]; pos += offset) {}
    }

    constexpr edge_iterator &operator++() noexcept {
        for(pos += offset; pos != last && !it[pos]; pos += offset) {}
        return *this;
    }

    constexpr edge_iterator operator++(int) noexcept {
        edge_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::make_pair<size_type>(pos / vert, pos % vert);
    }

    template<typename Type>
    friend constexpr bool operator==(const edge_iterator<Type> &, const edge_iterator<Type> &) noexcept;

private:
    It it;
    size_type vert;
    size_type pos;
    size_type last;
    size_type offset{};
};

template<typename Container>
[[nodiscard]] inline constexpr bool operator==(const edge_iterator<Container> &lhs, const edge_iterator<Container> &rhs) noexcept {
    return lhs.pos == rhs.pos;
}

template<typename Container>
[[nodiscard]] inline constexpr bool operator!=(const edge_iterator<Container> &lhs, const edge_iterator<Container> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic implementation of a directed adjacency matrix.
 * @tparam Category Either a directed or undirected category tag.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Category, typename Allocator>
class adjacency_matrix {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_base_of_v<directed_tag, Category>, "Invalid graph category");
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::size_t>, "Invalid value type");
    using container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Vertex type. */
    using vertex_type = size_type;
    /*! @brief Edge type. */
    using edge_type = std::pair<vertex_type, vertex_type>;
    /*! @brief Vertex iterator type. */
    using vertex_iterator = iota_iterator<vertex_type>;
    /*! @brief Edge iterator type. */
    using edge_iterator = internal::edge_iterator<typename container_type::const_iterator>;
    /*! @brief Out edge iterator type. */
    using out_edge_iterator = edge_iterator;
    /*! @brief In edge iterator type. */
    using in_edge_iterator = edge_iterator;
    /*! @brief Graph category tag. */
    using graph_category = Category;

    /*! @brief Default constructor. */
    adjacency_matrix() noexcept(noexcept(allocator_type{}))
        : adjacency_matrix{0u} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit adjacency_matrix(const allocator_type &allocator) noexcept
        : adjacency_matrix{0u, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied number of vertices.
     * @param vertices Number of vertices.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(const size_type vertices, const allocator_type &allocator = allocator_type{})
        : matrix{vertices * vertices, allocator},
          vert{vertices} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    adjacency_matrix(const adjacency_matrix &other)
        : adjacency_matrix{other, other.get_allocator()} {}

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(const adjacency_matrix &other, const allocator_type &allocator)
        : matrix{other.matrix, allocator},
          vert{other.vert} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    adjacency_matrix(adjacency_matrix &&other) noexcept
        : adjacency_matrix{std::move(other), other.get_allocator()} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(adjacency_matrix &&other, const allocator_type &allocator)
        : matrix{std::move(other.matrix), allocator},
          vert{std::exchange(other.vert, 0u)} {}

    /**
     * @brief Default copy assignment operator.
     * @param other The instance to copy from.
     * @return This container.
     */
    adjacency_matrix &operator=(const adjacency_matrix &other) {
        matrix = other.matrix;
        vert = other.vert;
        return *this;
    }

    /**
     * @brief Default move assignment operator.
     * @param other The instance to move from.
     * @return This container.
     */
    adjacency_matrix &operator=(adjacency_matrix &&other) noexcept {
        matrix = std::move(other.matrix);
        vert = std::exchange(other.vert, 0u);
        return *this;
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return matrix.get_allocator();
    }

    /*! @brief Clears the adjacency matrix. */
    void clear() noexcept {
        matrix.clear();
        vert = {};
    }

    /**
     * @brief Exchanges the contents with those of a given adjacency matrix.
     * @param other Adjacency matrix to exchange the content with.
     */
    void swap(adjacency_matrix &other) {
        using std::swap;
        swap(matrix, other.matrix);
        swap(vert, other.vert);
    }

    /**
     * @brief Returns the number of vertices.
     * @return The number of vertices.
     */
    [[nodiscard]] size_type size() const noexcept {
        return vert;
    }

    /**
     * @brief Returns an iterable object to visit all vertices of a matrix.
     * @return An iterable object to visit all vertices of a matrix.
     */
    [[nodiscard]] iterable_adaptor<vertex_iterator> vertices() const noexcept {
        return {0u, vert};
    }

    /**
     * @brief Returns an iterable object to visit all edges of a matrix.
     * @return An iterable object to visit all edges of a matrix.
     */
    [[nodiscard]] iterable_adaptor<edge_iterator> edges() const noexcept {
        const auto it = matrix.cbegin();
        const auto sz = matrix.size();
        return {{it, vert, 0u, sz, 1u}, {it, vert, sz, sz, 1u}};
    }

    /**
     * @brief Returns an iterable object to visit all out edges of a vertex.
     * @param vertex The vertex of which to return all out edges.
     * @return An iterable object to visit all out edges of a vertex.
     */
    [[nodiscard]] iterable_adaptor<out_edge_iterator> out_edges(const vertex_type vertex) const noexcept {
        const auto it = matrix.cbegin();
        const auto from = vertex * vert;
        const auto to = vertex * vert + vert;
        return {{it, vert, from, to, 1u}, {it, vert, to, to, 1u}};
    }

    /**
     * @brief Returns an iterable object to visit all in edges of a vertex.
     * @param vertex The vertex of which to return all in edges.
     * @return An iterable object to visit all in edges of a vertex.
     */
    [[nodiscard]] iterable_adaptor<in_edge_iterator> in_edges(const vertex_type vertex) const noexcept {
        const auto it = matrix.cbegin();
        const auto from = vertex;
        const auto to = vert * (vert - 1u) + vertex;
        return {{it, vert, from, to, vert}, {it, vert, to, to, vert}};
    }

    /**
     * @brief Resizes an adjacency matrix.
     * @param vertices The new number of vertices.
     */
    void resize(const size_type vertices) {
        adjacency_matrix other{vertices, get_allocator()};

        for(auto [lhs, rhs]: edges()) {
            other.insert(lhs, rhs);
        }

        other.swap(*this);
    }

    /**
     * @brief Inserts an edge into the adjacency matrix, if it does not exist.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<edge_iterator, bool> insert(const vertex_type lhs, const vertex_type rhs) {
        const auto pos = lhs * vert + rhs;

        if constexpr(std::is_same_v<graph_category, undirected_tag>) {
            const auto rev = rhs * vert + lhs;
            ENTT_ASSERT(matrix[pos] == matrix[rev], "Something went really wrong");
            matrix[rev] = 1u;
        }

        const auto inserted = !std::exchange(matrix[pos], 1u);
        return {edge_iterator{matrix.cbegin(), vert, pos, matrix.size(), 1u}, inserted};
    }

    /**
     * @brief Removes the edge associated with a pair of given vertices.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const vertex_type lhs, const vertex_type rhs) {
        const auto pos = lhs * vert + rhs;

        if constexpr(std::is_same_v<graph_category, undirected_tag>) {
            const auto rev = rhs * vert + lhs;
            ENTT_ASSERT(matrix[pos] == matrix[rev], "Something went really wrong");
            matrix[rev] = 0u;
        }

        return std::exchange(matrix[pos], 0u);
    }

    /**
     * @brief Checks if an adjacency matrix contains a given edge.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return True if there is such an edge, false otherwise.
     */
    [[nodiscard]] bool contains(const vertex_type lhs, const vertex_type rhs) const {
        const auto pos = lhs * vert + rhs;
        return pos < matrix.size() && matrix[pos];
    }

private:
    container_type matrix;
    size_type vert;
};

} // namespace entt

#endif

// #include "../graph/flow.hpp"
#ifndef ENTT_GRAPH_FLOW_HPP
#define ENTT_GRAPH_FLOW_HPP

#include <algorithm>
#include <cstddef>
#include <functional>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../container/dense_map.hpp"
#ifndef ENTT_CONTAINER_DENSE_MAP_HPP
#define ENTT_CONTAINER_DENSE_MAP_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CONTAINER_FWD_HPP
#define ENTT_CONTAINER_FWD_HPP

#include <functional>
#include <memory>

namespace entt {

template<
    typename Key,
    typename Type,
    typename = std::hash<Key>,
    typename = std::equal_to<Key>,
    typename = std::allocator<std::pair<const Key, Type>>>
class dense_map;

template<
    typename Type,
    typename = std::hash<Type>,
    typename = std::equal_to<Type>,
    typename = std::allocator<Type>>
class dense_set;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Key, typename Type>
struct dense_map_node final {
    using value_type = std::pair<Key, Type>;

    template<typename... Args>
    dense_map_node(const std::size_t pos, Args &&...args)
        : next{pos},
          element{std::forward<Args>(args)...} {}

    template<typename Allocator, typename... Args>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const std::size_t pos, Args &&...args)
        : next{pos},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::forward<Args>(args)...)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const dense_map_node &other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, other.element)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, dense_map_node &&other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::move(other.element))} {}

    std::size_t next;
    value_type element;
};

template<typename It>
class dense_map_iterator final {
    template<typename>
    friend class dense_map_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_iterator() noexcept
        : it{} {}

    constexpr dense_map_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_iterator(const dense_map_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_map_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_map_iterator operator++(int) noexcept {
        dense_map_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_map_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_map_iterator operator--(int) noexcept {
        dense_map_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_map_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_map_iterator operator+(const difference_type value) const noexcept {
        dense_map_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_map_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_map_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].element.first, it[value].element.second};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->element.first, it->element.second};
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_map_local_iterator final {
    template<typename>
    friend class dense_map_local_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_map_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_local_iterator(const dense_map_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_map_local_iterator &operator++() noexcept {
        return offset = it[offset].next, *this;
    }

    constexpr dense_map_local_iterator operator++(int) noexcept {
        dense_map_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it[offset].element.first, it[offset].element.second};
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for key-value pairs with unique keys.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on the hash of its key. Keys with the same hash
 * code appear in the same bucket.
 *
 * @tparam Key Key type of the associative container.
 * @tparam Type Mapped type of the associative container.
 * @tparam Hash Type of function to use to hash the keys.
 * @tparam KeyEqual Type of function to use to compare the keys for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Key, typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_map {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = internal::dense_map_node<Key, Type>;
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::pair<const Key, Type>>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t key_to_bucket(const Other &key) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(key)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other, typename... Args>
    [[nodiscard]] auto insert_or_do_nothing(Other &&key, Args &&...args) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::piecewise_construct, std::forward_as_tuple(std::forward<Other>(key)), std::forward_as_tuple(std::forward<Args>(args)...));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    template<typename Other, typename Arg>
    [[nodiscard]] auto insert_or_overwrite(Other &&key, Arg &&value) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            it->second = std::forward<Arg>(value);
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(key), std::forward<Arg>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + key_to_bucket(packed.first().back().element.first);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].next) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Key;
    /*! @brief Mapped type of the container. */
    using mapped_type = Type;
    /*! @brief Key-value type of the container. */
    using value_type = std::pair<const Key, Type>;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the keys. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the keys for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Input iterator type. */
    using iterator = internal::dense_map_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_iterator = internal::dense_map_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Input iterator type. */
    using local_iterator = internal::dense_map_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_local_iterator = internal::dense_map_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_map()
        : dense_map{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const allocator_type &allocator)
        : dense_map{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const allocator_type &allocator)
        : dense_map{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_map{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_map(const dense_map &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_map(const dense_map &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_map(dense_map &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_map(dense_map &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_map &operator=(const dense_map &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_map &operator=(dense_map &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if the key does not exist.
     * @param value A key-value pair eventually convertible to the value type.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value.first, value.second);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value.first), std::move(value.second));
    }

    /**
     * @copydoc insert
     * @tparam Arg Type of the key-value pair to insert into the container.
     */
    template<typename Arg>
    std::enable_if_t<std::is_constructible_v<value_type, Arg &&>, std::pair<iterator, bool>>
    insert(Arg &&value) {
        return insert_or_do_nothing(std::forward<Arg>(value).first, std::forward<Arg>(value).second);
    }

    /**
     * @brief Inserts elements into the container, if their keys do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Inserts an element into the container or assigns to the current
     * element if the key already exists.
     * @tparam Arg Type of the value to insert or assign.
     * @param key A key used both to look up and to insert if not found.
     * @param value A value to insert or assign.
     * @return A pair consisting of an iterator to the element and a bool
     * denoting whether the insertion took place.
     */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(const key_type &key, Arg &&value) {
        return insert_or_overwrite(key, std::forward<Arg>(value));
    }

    /*! @copydoc insert_or_assign */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(key_type &&key, Arg &&value) {
        return insert_or_overwrite(std::move(key), std::forward<Arg>(value));
    }

    /**
     * @brief Constructs an element in-place, if the key does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace([[maybe_unused]] Args &&...args) {
        if constexpr(sizeof...(Args) == 0u) {
            return insert_or_do_nothing(key_type{});
        } else if constexpr(sizeof...(Args) == 1u) {
            return insert_or_do_nothing(std::forward<Args>(args).first..., std::forward<Args>(args).second...);
        } else if constexpr(sizeof...(Args) == 2u) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(packed.first().size(), std::forward<Args>(args)...);
            const auto index = key_to_bucket(node.element.first);

            if(auto it = constrained_find(node.element.first, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.next, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Inserts in-place if the key does not exist, does nothing if the
     * key exists.
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param key A key used both to look up and to insert if not found.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(const key_type &key, Args &&...args) {
        return insert_or_do_nothing(key, std::forward<Args>(args)...);
    }

    /*! @copydoc try_emplace */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(key_type &&key, Args &&...args) {
        return insert_or_do_nothing(std::move(key), std::forward<Args>(args)...);
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(pos->first);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].element.first);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given key.
     * @param key A key value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const key_type &key) {
        for(size_type *curr = sparse.first().data() + key_to_bucket(key); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].next) {
            if(packed.second()(packed.first()[*curr].element.first, key)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].next;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_map &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Accesses a given element with bounds checking.
     * @param key A key of an element to find.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &at(const key_type &key) {
        auto it = find(key);
        ENTT_ASSERT(it != end(), "Invalid key");
        return it->second;
    }

    /*! @copydoc at */
    [[nodiscard]] const mapped_type &at(const key_type &key) const {
        auto it = find(key);
        ENTT_ASSERT(it != cend(), "Invalid key");
        return it->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](const key_type &key) {
        return insert_or_do_nothing(key).first->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](key_type &&key) {
        return insert_or_do_nothing(std::move(key)).first->second;
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const key_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given key.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const key_type &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const key_type &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Finds an element with a key that compares _equivalent_ to a given
     * key.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Returns a range containing all elements with a given key.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const key_type &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const key_type &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given key.
     * @tparam Other Type of an element to search for.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given key.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const key_type &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Checks if the container contains an element with a key that
     * compares _equivalent_ to a given value.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given key.
     * @param key The value of the key to examine.
     * @return The bucket for the given key.
     */
    [[nodiscard]] size_type bucket(const key_type &key) const {
        return key_to_bucket(key);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = key_to_bucket(packed.first()[pos].element.first);
                packed.first()[pos].next = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the keys.
     * @return The function used to hash the keys.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare keys for equality.
     * @return The function used to compare keys for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace std {

template<typename Key, typename Value, typename Allocator>
struct uses_allocator<entt::internal::dense_map_node<Key, Value>, Allocator>
    : std::true_type {};

} // namespace std

/**
 * Internal details not to be documented.
 * @endcond
 */

#endif

// #include "../container/dense_set.hpp"
#ifndef ENTT_CONTAINER_DENSE_SET_HPP
#define ENTT_CONTAINER_DENSE_SET_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/compressed_pair.hpp"

// #include "../core/memory.hpp"

// #include "../core/type_traits.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class dense_set_iterator final {
    template<typename>
    friend class dense_set_iterator;

public:
    using value_type = typename It::value_type::second_type;
    using pointer = const value_type *;
    using reference = const value_type &;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::random_access_iterator_tag;

    constexpr dense_set_iterator() noexcept
        : it{} {}

    constexpr dense_set_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_set_iterator(const dense_set_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_set_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_set_iterator operator++(int) noexcept {
        dense_set_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_set_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_set_iterator operator--(int) noexcept {
        dense_set_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_set_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_set_iterator operator+(const difference_type value) const noexcept {
        dense_set_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_set_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_set_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return it[value].second;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::addressof(it->second);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_set_local_iterator final {
    template<typename>
    friend class dense_set_local_iterator;

public:
    using value_type = typename It::value_type::second_type;
    using pointer = const value_type *;
    using reference = const value_type &;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::forward_iterator_tag;

    constexpr dense_set_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_set_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_set_local_iterator(const dense_set_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_set_local_iterator &operator++() noexcept {
        return offset = it[offset].first, *this;
    }

    constexpr dense_set_local_iterator operator++(int) noexcept {
        dense_set_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::addressof(it[offset].second);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_set_local_iterator<ILhs> &lhs, const dense_set_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_set_local_iterator<ILhs> &lhs, const dense_set_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for unique objects of a given type.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on its hash. Elements with the same hash code
 * appear in the same bucket.
 *
 * @tparam Type Value type of the associative container.
 * @tparam Hash Type of function to use to hash the values.
 * @tparam KeyEqual Type of function to use to compare the values for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_set {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = std::pair<std::size_t, Type>;
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t value_to_bucket(const Other &value) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(value)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &value, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(*it, value)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &value, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(*it, value)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other>
    [[nodiscard]] auto insert_or_do_nothing(Other &&value) {
        const auto index = value_to_bucket(value);

        if(auto it = constrained_find(value, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + value_to_bucket(packed.first().back().second);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].first) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Type;
    /*! @brief Value type of the container. */
    using value_type = Type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the elements. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the elements for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Random access iterator type. */
    using iterator = internal::dense_set_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant random access iterator type. */
    using const_iterator = internal::dense_set_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Forward iterator type. */
    using local_iterator = internal::dense_set_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant forward iterator type. */
    using const_local_iterator = internal::dense_set_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_set()
        : dense_set{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_set(const allocator_type &allocator)
        : dense_set{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_set(const size_type cnt, const allocator_type &allocator)
        : dense_set{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_set(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_set{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_set(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_set(const dense_set &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_set(const dense_set &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_set(dense_set &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_set(dense_set &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_set &operator=(const dense_set &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_set &operator=(dense_set &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if it does not exist.
     * @param value An element to insert into the container.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value));
    }

    /**
     * @brief Inserts elements into the container, if they do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Constructs an element in-place, if it does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace(Args &&...args) {
        if constexpr(((sizeof...(Args) == 1u) && ... && std::is_same_v<std::decay_t<Args>, value_type>)) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(std::piecewise_construct, std::make_tuple(packed.first().size()), std::forward_as_tuple(std::forward<Args>(args)...));
            const auto index = value_to_bucket(node.second);

            if(auto it = constrained_find(node.second, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.first, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(*pos);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].second);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given value.
     * @param value Value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const value_type &value) {
        for(size_type *curr = sparse.first().data() + value_to_bucket(value); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].first) {
            if(packed.second()(packed.first()[*curr].second, value)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].first;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_set &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Returns the number of elements matching a value (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const value_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given value.
     * @param value Value of an element to search for.
     * @return An iterator to an element with the given value. If no such
     * element is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const value_type &value) {
        return constrained_find(value, value_to_bucket(value));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const value_type &value) const {
        return constrained_find(value, value_to_bucket(value));
    }

    /**
     * @brief Finds an element that compares _equivalent_ to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return An iterator to an element with the given value. If no such
     * element is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &value) {
        return constrained_find(value, value_to_bucket(value));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &value) const {
        return constrained_find(value, value_to_bucket(value));
    }

    /**
     * @brief Returns a range containing all elements with a given value.
     * @param value Value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const value_type &value) {
        const auto it = find(value);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const value_type &value) const {
        const auto it = find(value);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &value) {
        const auto it = find(value);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &value) const {
        const auto it = find(value);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given value.
     * @param value Value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const value_type &value) const {
        return (find(value) != cend());
    }

    /**
     * @brief Checks if the container contains an element that compares
     * _equivalent_ to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &value) const {
        return (find(value) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given element.
     * @param value The value of the element to examine.
     * @return The bucket for the given element.
     */
    [[nodiscard]] size_type bucket(const value_type &value) const {
        return value_to_bucket(value);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = value_to_bucket(packed.first()[pos].second);
                packed.first()[pos].first = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the elements.
     * @return The function used to hash the elements.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare elements for equality.
     * @return The function used to compare elements for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/fwd.hpp"

// #include "../core/iterator.hpp"

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "adjacency_matrix.hpp"
#ifndef ENTT_GRAPH_ADJACENCY_MATRIX_HPP
#define ENTT_GRAPH_ADJACENCY_MATRIX_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/iterator.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class edge_iterator {
    using size_type = std::size_t;

public:
    using value_type = std::pair<size_type, size_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr edge_iterator() noexcept
        : it{},
          vert{},
          pos{},
          last{},
          offset{} {}

    constexpr edge_iterator(It base, const size_type vertices, const size_type from, const size_type to, const size_type step) noexcept
        : it{std::move(base)},
          vert{vertices},
          pos{from},
          last{to},
          offset{step} {
        for(; pos != last && !it[pos]; pos += offset) {}
    }

    constexpr edge_iterator &operator++() noexcept {
        for(pos += offset; pos != last && !it[pos]; pos += offset) {}
        return *this;
    }

    constexpr edge_iterator operator++(int) noexcept {
        edge_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::make_pair<size_type>(pos / vert, pos % vert);
    }

    template<typename Type>
    friend constexpr bool operator==(const edge_iterator<Type> &, const edge_iterator<Type> &) noexcept;

private:
    It it;
    size_type vert;
    size_type pos;
    size_type last;
    size_type offset{};
};

template<typename Container>
[[nodiscard]] inline constexpr bool operator==(const edge_iterator<Container> &lhs, const edge_iterator<Container> &rhs) noexcept {
    return lhs.pos == rhs.pos;
}

template<typename Container>
[[nodiscard]] inline constexpr bool operator!=(const edge_iterator<Container> &lhs, const edge_iterator<Container> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic implementation of a directed adjacency matrix.
 * @tparam Category Either a directed or undirected category tag.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Category, typename Allocator>
class adjacency_matrix {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_base_of_v<directed_tag, Category>, "Invalid graph category");
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::size_t>, "Invalid value type");
    using container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Vertex type. */
    using vertex_type = size_type;
    /*! @brief Edge type. */
    using edge_type = std::pair<vertex_type, vertex_type>;
    /*! @brief Vertex iterator type. */
    using vertex_iterator = iota_iterator<vertex_type>;
    /*! @brief Edge iterator type. */
    using edge_iterator = internal::edge_iterator<typename container_type::const_iterator>;
    /*! @brief Out edge iterator type. */
    using out_edge_iterator = edge_iterator;
    /*! @brief In edge iterator type. */
    using in_edge_iterator = edge_iterator;
    /*! @brief Graph category tag. */
    using graph_category = Category;

    /*! @brief Default constructor. */
    adjacency_matrix() noexcept(noexcept(allocator_type{}))
        : adjacency_matrix{0u} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit adjacency_matrix(const allocator_type &allocator) noexcept
        : adjacency_matrix{0u, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied number of vertices.
     * @param vertices Number of vertices.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(const size_type vertices, const allocator_type &allocator = allocator_type{})
        : matrix{vertices * vertices, allocator},
          vert{vertices} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    adjacency_matrix(const adjacency_matrix &other)
        : adjacency_matrix{other, other.get_allocator()} {}

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(const adjacency_matrix &other, const allocator_type &allocator)
        : matrix{other.matrix, allocator},
          vert{other.vert} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    adjacency_matrix(adjacency_matrix &&other) noexcept
        : adjacency_matrix{std::move(other), other.get_allocator()} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(adjacency_matrix &&other, const allocator_type &allocator)
        : matrix{std::move(other.matrix), allocator},
          vert{std::exchange(other.vert, 0u)} {}

    /**
     * @brief Default copy assignment operator.
     * @param other The instance to copy from.
     * @return This container.
     */
    adjacency_matrix &operator=(const adjacency_matrix &other) {
        matrix = other.matrix;
        vert = other.vert;
        return *this;
    }

    /**
     * @brief Default move assignment operator.
     * @param other The instance to move from.
     * @return This container.
     */
    adjacency_matrix &operator=(adjacency_matrix &&other) noexcept {
        matrix = std::move(other.matrix);
        vert = std::exchange(other.vert, 0u);
        return *this;
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return matrix.get_allocator();
    }

    /*! @brief Clears the adjacency matrix. */
    void clear() noexcept {
        matrix.clear();
        vert = {};
    }

    /**
     * @brief Exchanges the contents with those of a given adjacency matrix.
     * @param other Adjacency matrix to exchange the content with.
     */
    void swap(adjacency_matrix &other) {
        using std::swap;
        swap(matrix, other.matrix);
        swap(vert, other.vert);
    }

    /**
     * @brief Returns the number of vertices.
     * @return The number of vertices.
     */
    [[nodiscard]] size_type size() const noexcept {
        return vert;
    }

    /**
     * @brief Returns an iterable object to visit all vertices of a matrix.
     * @return An iterable object to visit all vertices of a matrix.
     */
    [[nodiscard]] iterable_adaptor<vertex_iterator> vertices() const noexcept {
        return {0u, vert};
    }

    /**
     * @brief Returns an iterable object to visit all edges of a matrix.
     * @return An iterable object to visit all edges of a matrix.
     */
    [[nodiscard]] iterable_adaptor<edge_iterator> edges() const noexcept {
        const auto it = matrix.cbegin();
        const auto sz = matrix.size();
        return {{it, vert, 0u, sz, 1u}, {it, vert, sz, sz, 1u}};
    }

    /**
     * @brief Returns an iterable object to visit all out edges of a vertex.
     * @param vertex The vertex of which to return all out edges.
     * @return An iterable object to visit all out edges of a vertex.
     */
    [[nodiscard]] iterable_adaptor<out_edge_iterator> out_edges(const vertex_type vertex) const noexcept {
        const auto it = matrix.cbegin();
        const auto from = vertex * vert;
        const auto to = vertex * vert + vert;
        return {{it, vert, from, to, 1u}, {it, vert, to, to, 1u}};
    }

    /**
     * @brief Returns an iterable object to visit all in edges of a vertex.
     * @param vertex The vertex of which to return all in edges.
     * @return An iterable object to visit all in edges of a vertex.
     */
    [[nodiscard]] iterable_adaptor<in_edge_iterator> in_edges(const vertex_type vertex) const noexcept {
        const auto it = matrix.cbegin();
        const auto from = vertex;
        const auto to = vert * (vert - 1u) + vertex;
        return {{it, vert, from, to, vert}, {it, vert, to, to, vert}};
    }

    /**
     * @brief Resizes an adjacency matrix.
     * @param vertices The new number of vertices.
     */
    void resize(const size_type vertices) {
        adjacency_matrix other{vertices, get_allocator()};

        for(auto [lhs, rhs]: edges()) {
            other.insert(lhs, rhs);
        }

        other.swap(*this);
    }

    /**
     * @brief Inserts an edge into the adjacency matrix, if it does not exist.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<edge_iterator, bool> insert(const vertex_type lhs, const vertex_type rhs) {
        const auto pos = lhs * vert + rhs;

        if constexpr(std::is_same_v<graph_category, undirected_tag>) {
            const auto rev = rhs * vert + lhs;
            ENTT_ASSERT(matrix[pos] == matrix[rev], "Something went really wrong");
            matrix[rev] = 1u;
        }

        const auto inserted = !std::exchange(matrix[pos], 1u);
        return {edge_iterator{matrix.cbegin(), vert, pos, matrix.size(), 1u}, inserted};
    }

    /**
     * @brief Removes the edge associated with a pair of given vertices.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const vertex_type lhs, const vertex_type rhs) {
        const auto pos = lhs * vert + rhs;

        if constexpr(std::is_same_v<graph_category, undirected_tag>) {
            const auto rev = rhs * vert + lhs;
            ENTT_ASSERT(matrix[pos] == matrix[rev], "Something went really wrong");
            matrix[rev] = 0u;
        }

        return std::exchange(matrix[pos], 0u);
    }

    /**
     * @brief Checks if an adjacency matrix contains a given edge.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return True if there is such an edge, false otherwise.
     */
    [[nodiscard]] bool contains(const vertex_type lhs, const vertex_type rhs) const {
        const auto pos = lhs * vert + rhs;
        return pos < matrix.size() && matrix[pos];
    }

private:
    container_type matrix;
    size_type vert;
};

} // namespace entt

#endif

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class for creating task graphs.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Allocator>
class basic_flow {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, id_type>, "Invalid value type");
    using task_container_type = dense_set<id_type, identity, std::equal_to<id_type>, typename alloc_traits::template rebind_alloc<id_type>>;
    using ro_rw_container_type = std::vector<std::pair<std::size_t, bool>, typename alloc_traits::template rebind_alloc<std::pair<std::size_t, bool>>>;
    using deps_container_type = dense_map<id_type, ro_rw_container_type, identity, std::equal_to<id_type>, typename alloc_traits::template rebind_alloc<std::pair<const id_type, ro_rw_container_type>>>;

    void emplace(const id_type res, const bool is_rw) {
        ENTT_ASSERT(index.first() < vertices.size(), "Invalid node");

        if(!deps.contains(res) && sync_on != vertices.size()) {
            deps[res].emplace_back(sync_on, true);
        }

        deps[res].emplace_back(index.first(), is_rw);
    }

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Iterable task list. */
    using iterable = iterable_adaptor<typename task_container_type::const_iterator>;

    /*! @brief Default constructor. */
    basic_flow()
        : basic_flow{allocator_type{}} {}

    /**
     * @brief Constructs a flow builder with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_flow(const allocator_type &allocator)
        : index{0u, allocator},
          vertices{},
          deps{},
          sync_on{} {}

    /*! @brief Default copy constructor. */
    basic_flow(const basic_flow &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    basic_flow(const basic_flow &other, const allocator_type &allocator)
        : index{other.index.first(), allocator},
          vertices{other.vertices, allocator},
          deps{other.deps, allocator},
          sync_on{other.sync_on} {}

    /*! @brief Default move constructor. */
    basic_flow(basic_flow &&) noexcept = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_flow(basic_flow &&other, const allocator_type &allocator)
        : index{other.index.first(), allocator},
          vertices{std::move(other.vertices), allocator},
          deps{std::move(other.deps), allocator},
          sync_on{other.sync_on} {}

    /**
     * @brief Default copy assignment operator.
     * @return This flow builder.
     */
    basic_flow &operator=(const basic_flow &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This flow builder.
     */
    basic_flow &operator=(basic_flow &&) noexcept = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return allocator_type{index.second()};
    }

    /**
     * @brief Returns the identifier at specified location.
     * @param pos Position of the identifier to return.
     * @return The requested identifier.
     */
    [[nodiscard]] id_type operator[](const size_type pos) const {
        return vertices.cbegin()[pos];
    }

    /*! @brief Clears the flow builder. */
    void clear() noexcept {
        index.first() = sync_on = {};
        vertices.clear();
        deps.clear();
    }

    /**
     * @brief Exchanges the contents with those of a given flow builder.
     * @param other Flow builder to exchange the content with.
     */
    void swap(basic_flow &other) {
        using std::swap;
        std::swap(index, other.index);
        std::swap(vertices, other.vertices);
        std::swap(deps, other.deps);
        std::swap(sync_on, other.sync_on);
    }

    /**
     * @brief Returns the number of tasks.
     * @return The number of tasks.
     */
    [[nodiscard]] size_type size() const noexcept {
        return vertices.size();
    }

    /**
     * @brief Binds a task to a flow builder.
     * @param value Task identifier.
     * @return This flow builder.
     */
    basic_flow &bind(const id_type value) {
        sync_on += (sync_on == vertices.size());
        const auto it = vertices.emplace(value).first;
        index.first() = size_type(it - vertices.begin());
        return *this;
    }

    /**
     * @brief Turns the current task into a sync point.
     * @return This flow builder.
     */
    basic_flow &sync() {
        ENTT_ASSERT(index.first() < vertices.size(), "Invalid node");
        sync_on = index.first();

        for(const auto &elem: deps) {
            elem.second.emplace_back(sync_on, true);
        }

        return *this;
    }

    /**
     * @brief Assigns a resource to the current task with a given access mode.
     * @param res Resource identifier.
     * @param is_rw Access mode.
     * @return This flow builder.
     */
    basic_flow &set(const id_type res, bool is_rw = false) {
        emplace(res, is_rw);
        return *this;
    }

    /**
     * @brief Assigns a read-only resource to the current task.
     * @param res Resource identifier.
     * @return This flow builder.
     */
    basic_flow &ro(const id_type res) {
        emplace(res, false);
        return *this;
    }

    /**
     * @brief Assigns a range of read-only resources to the current task.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return This flow builder.
     */
    template<typename It>
    std::enable_if_t<std::is_same_v<std::remove_const_t<typename std::iterator_traits<It>::value_type>, id_type>, basic_flow &>
    ro(It first, It last) {
        for(; first != last; ++first) {
            emplace(*first, false);
        }

        return *this;
    }

    /**
     * @brief Assigns a writable resource to the current task.
     * @param res Resource identifier.
     * @return This flow builder.
     */
    basic_flow &rw(const id_type res) {
        emplace(res, true);
        return *this;
    }

    /**
     * @brief Assigns a range of writable resources to the current task.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return This flow builder.
     */
    template<typename It>
    std::enable_if_t<std::is_same_v<std::remove_const_t<typename std::iterator_traits<It>::value_type>, id_type>, basic_flow &>
    rw(It first, It last) {
        for(; first != last; ++first) {
            emplace(*first, true);
        }

        return *this;
    }

    /**
     * @brief Generates a task graph for the current content.
     * @return The adjacency matrix of the task graph.
     */
    [[nodiscard]] adjacency_matrix<directed_tag> graph() const {
        const auto length = vertices.size();
        adjacency_matrix<directed_tag> matrix{length};

        // creates the adjacency matrix
        for(const auto &elem: deps) {
            const auto last = elem.second.cend();
            auto it = elem.second.cbegin();

            while(it != last) {
                if(it->second) {
                    // rw item
                    if(auto curr = it++; it != last) {
                        if(it->second) {
                            matrix.insert(curr->first, it->first);
                        } else if(const auto next = std::find_if(it, last, [](const auto &value) { return value.second; }); next != last) {
                            for(; it != next; ++it) {
                                matrix.insert(curr->first, it->first);
                                matrix.insert(it->first, next->first);
                            }
                        } else {
                            for(; it != next; ++it) {
                                matrix.insert(curr->first, it->first);
                            }
                        }
                    }
                } else {
                    // ro item (first iteration only)
                    if(const auto next = std::find_if(it, last, [](const auto &value) { return value.second; }); next != last) {
                        for(; it != next; ++it) {
                            matrix.insert(it->first, next->first);
                        }
                    } else {
                        it = last;
                    }
                }
            }
        }

        // computes the transitive closure
        for(std::size_t vk{}; vk < length; ++vk) {
            for(std::size_t vi{}; vi < length; ++vi) {
                for(std::size_t vj{}; vj < length; ++vj) {
                    if(matrix.contains(vi, vk) && matrix.contains(vk, vj)) {
                        matrix.insert(vi, vj);
                    }
                }
            }
        }

        // applies the transitive reduction
        for(std::size_t vert{}; vert < length; ++vert) {
            matrix.erase(vert, vert);
        }

        for(std::size_t vj{}; vj < length; ++vj) {
            for(std::size_t vi{}; vi < length; ++vi) {
                if(matrix.contains(vi, vj)) {
                    for(std::size_t vk{}; vk < length; ++vk) {
                        if(matrix.contains(vj, vk)) {
                            matrix.erase(vi, vk);
                        }
                    }
                }
            }
        }

        return matrix;
    }

private:
    compressed_pair<size_type, allocator_type> index;
    task_container_type vertices;
    deps_container_type deps;
    size_type sync_on;
};

} // namespace entt

#endif

// #include "fwd.hpp"

// #include "helper.hpp"
#ifndef ENTT_ENTITY_HELPER_HPP
#define ENTT_ENTITY_HELPER_HPP

#include <memory>
#include <type_traits>
// #include "../core/fwd.hpp"

// #include "../core/type_traits.hpp"

// #include "../signal/delegate.hpp"

// #include "component.hpp"

// #include "fwd.hpp"

// #include "group.hpp"

// #include "view.hpp"


namespace entt {

/**
 * @brief Converts a registry to a view.
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class as_view {
    template<typename... Get, typename... Exclude>
    auto dispatch(get_t<Get...>, exclude_t<Exclude...>) const {
        return reg.template view<constness_as_t<typename Get::value_type, Get>...>(exclude_t<constness_as_t<typename Exclude::value_type, Exclude>...>{});
    }

public:
    /*! @brief Type of registry to convert. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = std::remove_const_t<typename registry_type::entity_type>;

    /**
     * @brief Constructs a converter for a given registry.
     * @param source A valid reference to a registry.
     */
    as_view(registry_type &source) noexcept
        : reg{source} {}

    /**
     * @brief Conversion function from a registry to a view.
     * @tparam Get Type of storage used to construct the view.
     * @tparam Exclude Types of storage used to filter the view.
     * @return A newly created view.
     */
    template<typename Get, typename Exclude>
    operator basic_view<Get, Exclude>() const {
        return dispatch(Get{}, Exclude{});
    }

private:
    registry_type &reg;
};

/**
 * @brief Converts a registry to a group.
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class as_group {
    template<typename... Owned, typename... Get, typename... Exclude>
    auto dispatch(owned_t<Owned...>, get_t<Get...>, exclude_t<Exclude...>) const {
        if constexpr(std::is_const_v<registry_type>) {
            return reg.template group_if_exists<typename Owned::value_type...>(get_t<typename Get::value_type...>{}, exclude_t<typename Exclude::value_type...>{});
        } else {
            return reg.template group<constness_as_t<typename Owned::value_type, Owned>...>(get_t<constness_as_t<typename Get::value_type, Get>...>{}, exclude_t<constness_as_t<typename Exclude::value_type, Exclude>...>{});
        }
    }

public:
    /*! @brief Type of registry to convert. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = std::remove_const_t<typename registry_type::entity_type>;

    /**
     * @brief Constructs a converter for a given registry.
     * @param source A valid reference to a registry.
     */
    as_group(registry_type &source) noexcept
        : reg{source} {}

    /**
     * @brief Conversion function from a registry to a group.
     * @tparam Owned Types of _owned_ by the group.
     * @tparam Get Types of storage _observed_ by the group.
     * @tparam Exclude Types of storage used to filter the group.
     * @return A newly created group.
     */
    template<typename Owned, typename Get, typename Exclude>
    operator basic_group<Owned, Get, Exclude>() const {
        return dispatch(Owned{}, Get{}, Exclude{});
    }

private:
    registry_type &reg;
};

/**
 * @brief Helper to create a listener that directly invokes a member function.
 * @tparam Member Member function to invoke on a component of the given type.
 * @tparam Registry Basic registry type.
 * @param reg A registry that contains the given entity and its components.
 * @param entt Entity from which to get the component.
 */
template<auto Member, typename Registry = std::decay_t<nth_argument_t<0u, Member>>>
void invoke(Registry &reg, const typename Registry::entity_type entt) {
    static_assert(std::is_member_function_pointer_v<decltype(Member)>, "Invalid pointer to non-static member function");
    delegate<void(Registry &, const typename Registry::entity_type)> func;
    func.template connect<Member>(reg.template get<member_class_t<decltype(Member)>>(entt));
    func(reg, entt);
}

/**
 * @brief Returns the entity associated with a given component.
 *
 * @warning
 * Currently, this function only works correctly with the default pool as it
 * makes assumptions about how the components are laid out.
 *
 * @tparam Registry Basic registry type.
 * @tparam Component Type of component.
 * @param reg A registry that contains the given entity and its components.
 * @param instance A valid component instance.
 * @return The entity associated with the given component.
 */
template<typename Registry, typename Component>
typename Registry::entity_type to_entity(const Registry &reg, const Component &instance) {
    const auto &storage = reg.template storage<Component>();
    const typename Registry::base_type &base = storage;
    const auto *addr = std::addressof(instance);

    for(auto it = base.rbegin(), last = base.rend(); it < last; it += component_traits<Component>::page_size) {
        if(const auto dist = (addr - std::addressof(storage.get(*it))); dist >= 0 && dist < static_cast<decltype(dist)>(component_traits<Component>::page_size)) {
            return *(it + dist);
        }
    }

    return null;
}

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename>
struct is_view: std::false_type {};

template<typename... Args>
struct is_view<basic_view<Args...>>: std::true_type {};

template<typename Type>
inline constexpr bool is_view_v = is_view<Type>::value;

template<typename Type, typename Override>
struct unpack_type {
    using ro = std::conditional_t<
        type_list_contains_v<Override, const Type> || (std::is_const_v<Type> && !type_list_contains_v<Override, std::remove_const_t<Type>>),
        type_list<std::remove_const_t<Type>>,
        type_list<>>;

    using rw = std::conditional_t<
        type_list_contains_v<Override, std::remove_const_t<Type>> || (!std::is_const_v<Type> && !type_list_contains_v<Override, const Type>),
        type_list<Type>,
        type_list<>>;
};

template<typename... Args, typename... Override>
struct unpack_type<basic_registry<Args...>, type_list<Override...>> {
    using ro = type_list<>;
    using rw = type_list<>;
};

template<typename... Args, typename... Override>
struct unpack_type<const basic_registry<Args...>, type_list<Override...>>
    : unpack_type<basic_registry<Args...>, type_list<Override...>> {};

template<typename... Get, typename... Exclude, typename... Override>
struct unpack_type<basic_view<get_t<Get...>, exclude_t<Exclude...>>, type_list<Override...>> {
    using ro = type_list_cat_t<type_list<typename Exclude::value_type...>, typename unpack_type<constness_as_t<typename Get::value_type, Get>, type_list<Override...>>::ro...>;
    using rw = type_list_cat_t<typename unpack_type<constness_as_t<typename Get::value_type, Get>, type_list<Override...>>::rw...>;
};

template<typename... Get, typename... Exclude, typename... Override>
struct unpack_type<const basic_view<get_t<Get...>, exclude_t<Exclude...>>, type_list<Override...>>
    : unpack_type<basic_view<get_t<Get...>, exclude_t<Exclude...>>, type_list<Override...>> {};

template<typename, typename>
struct resource_traits;

template<typename... Args, typename... Req>
struct resource_traits<type_list<Args...>, type_list<Req...>> {
    using args = type_list<std::remove_const_t<Args>...>;
    using ro = type_list_cat_t<typename unpack_type<Args, type_list<Req...>>::ro..., typename unpack_type<Req, type_list<>>::ro...>;
    using rw = type_list_cat_t<typename unpack_type<Args, type_list<Req...>>::rw..., typename unpack_type<Req, type_list<>>::rw...>;
};

template<typename... Req, typename Ret, typename... Args>
resource_traits<type_list<std::remove_reference_t<Args>...>, type_list<Req...>> free_function_to_resource_traits(Ret (*)(Args...));

template<typename... Req, typename Ret, typename Type, typename... Args>
resource_traits<type_list<std::remove_reference_t<Args>...>, type_list<Req...>> constrained_function_to_resource_traits(Ret (*)(Type &, Args...));

template<typename... Req, typename Ret, typename Class, typename... Args>
resource_traits<type_list<std::remove_reference_t<Args>...>, type_list<Req...>> constrained_function_to_resource_traits(Ret (Class::*)(Args...));

template<typename... Req, typename Ret, typename Class, typename... Args>
resource_traits<type_list<std::remove_reference_t<Args>...>, type_list<Req...>> constrained_function_to_resource_traits(Ret (Class::*)(Args...) const);

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Utility class for creating a static task graph.
 *
 * This class offers minimal support (but sufficient in many cases) for creating
 * an execution graph from functions and their requirements on resources.<br/>
 * Note that the resulting tasks aren't executed in any case. This isn't the
 * goal of the tool. Instead, they are returned to the user in the form of a
 * graph that allows for safe execution.
 *
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class basic_organizer final {
    using callback_type = void(const void *, Registry &);
    using prepare_type = void(Registry &);
    using dependency_type = std::size_t(const bool, const type_info **, const std::size_t);

    struct vertex_data final {
        std::size_t ro_count{};
        std::size_t rw_count{};
        const char *name{};
        const void *payload{};
        callback_type *callback{};
        dependency_type *dependency;
        prepare_type *prepare{};
        const type_info *info{};
    };

    template<typename Type>
    [[nodiscard]] static decltype(auto) extract(Registry &reg) {
        if constexpr(std::is_same_v<Type, Registry>) {
            return reg;
        } else if constexpr(internal::is_view_v<Type>) {
            return as_view{reg};
        } else {
            return reg.ctx().template emplace<std::remove_reference_t<Type>>();
        }
    }

    template<typename... Args>
    [[nodiscard]] static auto to_args(Registry &reg, type_list<Args...>) {
        return std::tuple<decltype(extract<Args>(reg))...>(extract<Args>(reg)...);
    }

    template<typename... Type>
    static std::size_t fill_dependencies(type_list<Type...>, [[maybe_unused]] const type_info **buffer, [[maybe_unused]] const std::size_t count) {
        if constexpr(sizeof...(Type) == 0u) {
            return {};
        } else {
            const type_info *info[sizeof...(Type)]{&type_id<Type>()...};
            const auto length = count < sizeof...(Type) ? count : sizeof...(Type);

            for(std::size_t pos{}; pos < length; ++pos) {
                buffer[pos] = info[pos];
            }

            return length;
        }
    }

    template<typename... RO, typename... RW>
    void track_dependencies(std::size_t index, const bool requires_registry, type_list<RO...>, type_list<RW...>) {
        builder.bind(static_cast<id_type>(index));
        builder.set(type_hash<Registry>::value(), requires_registry || (sizeof...(RO) + sizeof...(RW) == 0u));
        (builder.ro(type_hash<RO>::value()), ...);
        (builder.rw(type_hash<RW>::value()), ...);
    }

public:
    /*! Basic registry type. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename registry_type::entity_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Raw task function type. */
    using function_type = callback_type;

    /*! @brief Vertex type of a task graph defined as an adjacency list. */
    struct vertex {
        /**
         * @brief Constructs a vertex of the task graph.
         * @param vtype True if the vertex is a top-level one, false otherwise.
         * @param data The data associated with the vertex.
         * @param edges The indices of the children in the adjacency list.
         */
        vertex(const bool vtype, vertex_data data, std::vector<std::size_t> edges)
            : is_top_level{vtype},
              node{std::move(data)},
              reachable{std::move(edges)} {}

        /**
         * @brief Fills a buffer with the type info objects for the writable
         * resources of a vertex.
         * @param buffer A buffer pre-allocated by the user.
         * @param length The length of the user-supplied buffer.
         * @return The number of type info objects written to the buffer.
         */
        size_type ro_dependency(const type_info **buffer, const std::size_t length) const noexcept {
            return node.dependency(false, buffer, length);
        }

        /**
         * @brief Fills a buffer with the type info objects for the read-only
         * resources of a vertex.
         * @param buffer A buffer pre-allocated by the user.
         * @param length The length of the user-supplied buffer.
         * @return The number of type info objects written to the buffer.
         */
        size_type rw_dependency(const type_info **buffer, const std::size_t length) const noexcept {
            return node.dependency(true, buffer, length);
        }

        /**
         * @brief Returns the number of read-only resources of a vertex.
         * @return The number of read-only resources of the vertex.
         */
        size_type ro_count() const noexcept {
            return node.ro_count;
        }

        /**
         * @brief Returns the number of writable resources of a vertex.
         * @return The number of writable resources of the vertex.
         */
        size_type rw_count() const noexcept {
            return node.rw_count;
        }

        /**
         * @brief Checks if a vertex is also a top-level one.
         * @return True if the vertex is a top-level one, false otherwise.
         */
        bool top_level() const noexcept {
            return is_top_level;
        }

        /**
         * @brief Returns a type info object associated with a vertex.
         * @return A properly initialized type info object.
         */
        const type_info &info() const noexcept {
            return *node.info;
        }

        /**
         * @brief Returns a user defined name associated with a vertex, if any.
         * @return The user defined name associated with the vertex, if any.
         */
        const char *name() const noexcept {
            return node.name;
        }

        /**
         * @brief Returns the function associated with a vertex.
         * @return The function associated with the vertex.
         */
        function_type *callback() const noexcept {
            return node.callback;
        }

        /**
         * @brief Returns the payload associated with a vertex, if any.
         * @return The payload associated with the vertex, if any.
         */
        const void *data() const noexcept {
            return node.payload;
        }

        /**
         * @brief Returns the list of nodes reachable from a given vertex.
         * @return The list of nodes reachable from the vertex.
         */
        const std::vector<std::size_t> &children() const noexcept {
            return reachable;
        }

        /**
         * @brief Prepares a registry and assures that all required resources
         * are properly instantiated before using them.
         * @param reg A valid registry.
         */
        void prepare(registry_type &reg) const {
            node.prepare ? node.prepare(reg) : void();
        }

    private:
        bool is_top_level;
        vertex_data node;
        std::vector<std::size_t> reachable;
    };

    /**
     * @brief Adds a free function to the task list.
     * @tparam Candidate Function to add to the task list.
     * @tparam Req Additional requirements and/or override resource access mode.
     * @param name Optional name to associate with the task.
     */
    template<auto Candidate, typename... Req>
    void emplace(const char *name = nullptr) {
        using resource_type = decltype(internal::free_function_to_resource_traits<Req...>(Candidate));
        constexpr auto requires_registry = type_list_contains_v<typename resource_type::args, registry_type>;

        callback_type *callback = +[](const void *, registry_type &reg) {
            std::apply(Candidate, to_args(reg, typename resource_type::args{}));
        };

        vertex_data vdata{
            resource_type::ro::size,
            resource_type::rw::size,
            name,
            nullptr,
            callback,
            +[](const bool rw, const type_info **buffer, const std::size_t length) { return rw ? fill_dependencies(typename resource_type::rw{}, buffer, length) : fill_dependencies(typename resource_type::ro{}, buffer, length); },
            +[](registry_type &reg) { void(to_args(reg, typename resource_type::args{})); },
            &type_id<std::integral_constant<decltype(Candidate), Candidate>>()};

        track_dependencies(vertices.size(), requires_registry, typename resource_type::ro{}, typename resource_type::rw{});
        vertices.push_back(std::move(vdata));
    }

    /**
     * @brief Adds a free function with payload or a member function with an
     * instance to the task list.
     * @tparam Candidate Function or member to add to the task list.
     * @tparam Req Additional requirements and/or override resource access mode.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     * @param name Optional name to associate with the task.
     */
    template<auto Candidate, typename... Req, typename Type>
    void emplace(Type &value_or_instance, const char *name = nullptr) {
        using resource_type = decltype(internal::constrained_function_to_resource_traits<Req...>(Candidate));
        constexpr auto requires_registry = type_list_contains_v<typename resource_type::args, registry_type>;

        callback_type *callback = +[](const void *payload, registry_type &reg) {
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            std::apply(Candidate, std::tuple_cat(std::forward_as_tuple(*curr), to_args(reg, typename resource_type::args{})));
        };

        vertex_data vdata{
            resource_type::ro::size,
            resource_type::rw::size,
            name,
            &value_or_instance,
            callback,
            +[](const bool rw, const type_info **buffer, const std::size_t length) { return rw ? fill_dependencies(typename resource_type::rw{}, buffer, length) : fill_dependencies(typename resource_type::ro{}, buffer, length); },
            +[](registry_type &reg) { void(to_args(reg, typename resource_type::args{})); },
            &type_id<std::integral_constant<decltype(Candidate), Candidate>>()};

        track_dependencies(vertices.size(), requires_registry, typename resource_type::ro{}, typename resource_type::rw{});
        vertices.push_back(std::move(vdata));
    }

    /**
     * @brief Adds an user defined function with optional payload to the task
     * list.
     * @tparam Req Additional requirements and/or override resource access mode.
     * @param func Function to add to the task list.
     * @param payload User defined arbitrary data.
     * @param name Optional name to associate with the task.
     */
    template<typename... Req>
    void emplace(function_type *func, const void *payload = nullptr, const char *name = nullptr) {
        using resource_type = internal::resource_traits<type_list<>, type_list<Req...>>;
        track_dependencies(vertices.size(), true, typename resource_type::ro{}, typename resource_type::rw{});

        vertex_data vdata{
            resource_type::ro::size,
            resource_type::rw::size,
            name,
            payload,
            func,
            +[](const bool rw, const type_info **buffer, const std::size_t length) { return rw ? fill_dependencies(typename resource_type::rw{}, buffer, length) : fill_dependencies(typename resource_type::ro{}, buffer, length); },
            nullptr,
            &type_id<void>()};

        vertices.push_back(std::move(vdata));
    }

    /**
     * @brief Generates a task graph for the current content.
     * @return The adjacency list of the task graph.
     */
    std::vector<vertex> graph() {
        std::vector<vertex> adjacency_list{};
        adjacency_list.reserve(vertices.size());
        auto adjacency_matrix = builder.graph();

        for(auto curr: adjacency_matrix.vertices()) {
            const auto iterable = adjacency_matrix.in_edges(curr);
            std::vector<std::size_t> reachable{};

            for(auto &&edge: adjacency_matrix.out_edges(curr)) {
                reachable.push_back(edge.second);
            }

            adjacency_list.emplace_back(iterable.cbegin() == iterable.cend(), vertices[curr], std::move(reachable));
        }

        return adjacency_list;
    }

    /*! @brief Erases all elements from a container. */
    void clear() {
        builder.clear();
        vertices.clear();
    }

private:
    std::vector<vertex_data> vertices;
    flow builder;
};

} // namespace entt

#endif

// #include "entity/registry.hpp"
#ifndef ENTT_ENTITY_REGISTRY_HPP
#define ENTT_ENTITY_REGISTRY_HPP

#include <algorithm>
#include <cstddef>
#include <functional>
#include <iterator>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../container/dense_map.hpp"
#ifndef ENTT_CONTAINER_DENSE_MAP_HPP
#define ENTT_CONTAINER_DENSE_MAP_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CONTAINER_FWD_HPP
#define ENTT_CONTAINER_FWD_HPP

#include <functional>
#include <memory>

namespace entt {

template<
    typename Key,
    typename Type,
    typename = std::hash<Key>,
    typename = std::equal_to<Key>,
    typename = std::allocator<std::pair<const Key, Type>>>
class dense_map;

template<
    typename Type,
    typename = std::hash<Type>,
    typename = std::equal_to<Type>,
    typename = std::allocator<Type>>
class dense_set;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Key, typename Type>
struct dense_map_node final {
    using value_type = std::pair<Key, Type>;

    template<typename... Args>
    dense_map_node(const std::size_t pos, Args &&...args)
        : next{pos},
          element{std::forward<Args>(args)...} {}

    template<typename Allocator, typename... Args>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const std::size_t pos, Args &&...args)
        : next{pos},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::forward<Args>(args)...)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const dense_map_node &other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, other.element)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, dense_map_node &&other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::move(other.element))} {}

    std::size_t next;
    value_type element;
};

template<typename It>
class dense_map_iterator final {
    template<typename>
    friend class dense_map_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_iterator() noexcept
        : it{} {}

    constexpr dense_map_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_iterator(const dense_map_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_map_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_map_iterator operator++(int) noexcept {
        dense_map_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_map_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_map_iterator operator--(int) noexcept {
        dense_map_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_map_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_map_iterator operator+(const difference_type value) const noexcept {
        dense_map_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_map_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_map_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].element.first, it[value].element.second};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->element.first, it->element.second};
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_map_local_iterator final {
    template<typename>
    friend class dense_map_local_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_map_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_local_iterator(const dense_map_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_map_local_iterator &operator++() noexcept {
        return offset = it[offset].next, *this;
    }

    constexpr dense_map_local_iterator operator++(int) noexcept {
        dense_map_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it[offset].element.first, it[offset].element.second};
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for key-value pairs with unique keys.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on the hash of its key. Keys with the same hash
 * code appear in the same bucket.
 *
 * @tparam Key Key type of the associative container.
 * @tparam Type Mapped type of the associative container.
 * @tparam Hash Type of function to use to hash the keys.
 * @tparam KeyEqual Type of function to use to compare the keys for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Key, typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_map {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = internal::dense_map_node<Key, Type>;
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::pair<const Key, Type>>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t key_to_bucket(const Other &key) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(key)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other, typename... Args>
    [[nodiscard]] auto insert_or_do_nothing(Other &&key, Args &&...args) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::piecewise_construct, std::forward_as_tuple(std::forward<Other>(key)), std::forward_as_tuple(std::forward<Args>(args)...));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    template<typename Other, typename Arg>
    [[nodiscard]] auto insert_or_overwrite(Other &&key, Arg &&value) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            it->second = std::forward<Arg>(value);
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(key), std::forward<Arg>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + key_to_bucket(packed.first().back().element.first);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].next) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Key;
    /*! @brief Mapped type of the container. */
    using mapped_type = Type;
    /*! @brief Key-value type of the container. */
    using value_type = std::pair<const Key, Type>;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the keys. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the keys for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Input iterator type. */
    using iterator = internal::dense_map_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_iterator = internal::dense_map_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Input iterator type. */
    using local_iterator = internal::dense_map_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_local_iterator = internal::dense_map_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_map()
        : dense_map{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const allocator_type &allocator)
        : dense_map{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const allocator_type &allocator)
        : dense_map{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_map{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_map(const dense_map &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_map(const dense_map &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_map(dense_map &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_map(dense_map &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_map &operator=(const dense_map &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_map &operator=(dense_map &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if the key does not exist.
     * @param value A key-value pair eventually convertible to the value type.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value.first, value.second);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value.first), std::move(value.second));
    }

    /**
     * @copydoc insert
     * @tparam Arg Type of the key-value pair to insert into the container.
     */
    template<typename Arg>
    std::enable_if_t<std::is_constructible_v<value_type, Arg &&>, std::pair<iterator, bool>>
    insert(Arg &&value) {
        return insert_or_do_nothing(std::forward<Arg>(value).first, std::forward<Arg>(value).second);
    }

    /**
     * @brief Inserts elements into the container, if their keys do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Inserts an element into the container or assigns to the current
     * element if the key already exists.
     * @tparam Arg Type of the value to insert or assign.
     * @param key A key used both to look up and to insert if not found.
     * @param value A value to insert or assign.
     * @return A pair consisting of an iterator to the element and a bool
     * denoting whether the insertion took place.
     */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(const key_type &key, Arg &&value) {
        return insert_or_overwrite(key, std::forward<Arg>(value));
    }

    /*! @copydoc insert_or_assign */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(key_type &&key, Arg &&value) {
        return insert_or_overwrite(std::move(key), std::forward<Arg>(value));
    }

    /**
     * @brief Constructs an element in-place, if the key does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace([[maybe_unused]] Args &&...args) {
        if constexpr(sizeof...(Args) == 0u) {
            return insert_or_do_nothing(key_type{});
        } else if constexpr(sizeof...(Args) == 1u) {
            return insert_or_do_nothing(std::forward<Args>(args).first..., std::forward<Args>(args).second...);
        } else if constexpr(sizeof...(Args) == 2u) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(packed.first().size(), std::forward<Args>(args)...);
            const auto index = key_to_bucket(node.element.first);

            if(auto it = constrained_find(node.element.first, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.next, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Inserts in-place if the key does not exist, does nothing if the
     * key exists.
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param key A key used both to look up and to insert if not found.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(const key_type &key, Args &&...args) {
        return insert_or_do_nothing(key, std::forward<Args>(args)...);
    }

    /*! @copydoc try_emplace */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(key_type &&key, Args &&...args) {
        return insert_or_do_nothing(std::move(key), std::forward<Args>(args)...);
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(pos->first);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].element.first);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given key.
     * @param key A key value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const key_type &key) {
        for(size_type *curr = sparse.first().data() + key_to_bucket(key); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].next) {
            if(packed.second()(packed.first()[*curr].element.first, key)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].next;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_map &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Accesses a given element with bounds checking.
     * @param key A key of an element to find.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &at(const key_type &key) {
        auto it = find(key);
        ENTT_ASSERT(it != end(), "Invalid key");
        return it->second;
    }

    /*! @copydoc at */
    [[nodiscard]] const mapped_type &at(const key_type &key) const {
        auto it = find(key);
        ENTT_ASSERT(it != cend(), "Invalid key");
        return it->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](const key_type &key) {
        return insert_or_do_nothing(key).first->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](key_type &&key) {
        return insert_or_do_nothing(std::move(key)).first->second;
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const key_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given key.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const key_type &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const key_type &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Finds an element with a key that compares _equivalent_ to a given
     * key.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Returns a range containing all elements with a given key.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const key_type &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const key_type &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given key.
     * @tparam Other Type of an element to search for.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given key.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const key_type &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Checks if the container contains an element with a key that
     * compares _equivalent_ to a given value.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given key.
     * @param key The value of the key to examine.
     * @return The bucket for the given key.
     */
    [[nodiscard]] size_type bucket(const key_type &key) const {
        return key_to_bucket(key);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = key_to_bucket(packed.first()[pos].element.first);
                packed.first()[pos].next = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the keys.
     * @return The function used to hash the keys.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare keys for equality.
     * @return The function used to compare keys for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace std {

template<typename Key, typename Value, typename Allocator>
struct uses_allocator<entt::internal::dense_map_node<Key, Value>, Allocator>
    : std::true_type {};

} // namespace std

/**
 * Internal details not to be documented.
 * @endcond
 */

#endif

// #include "../core/algorithm.hpp"

// #include "../core/any.hpp"

// #include "../core/compressed_pair.hpp"

// #include "../core/fwd.hpp"

// #include "../core/iterator.hpp"

// #include "../core/memory.hpp"

// #include "../core/type_info.hpp"

// #include "../core/type_traits.hpp"

// #include "../core/utility.hpp"

// #include "component.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"

// #include "group.hpp"

// #include "sparse_set.hpp"

// #include "storage.hpp"

// #include "view.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class registry_storage_iterator final {
    template<typename Other>
    friend class registry_storage_iterator;

    using mapped_type = std::remove_reference_t<decltype(std::declval<It>()->second)>;

public:
    using value_type = std::pair<id_type, constness_as_t<typename mapped_type::element_type, mapped_type> &>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr registry_storage_iterator() noexcept
        : it{} {}

    constexpr registry_storage_iterator(It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr registry_storage_iterator(const registry_storage_iterator<Other> &other) noexcept
        : registry_storage_iterator{other.it} {}

    constexpr registry_storage_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr registry_storage_iterator operator++(int) noexcept {
        registry_storage_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr registry_storage_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr registry_storage_iterator operator--(int) noexcept {
        registry_storage_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr registry_storage_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr registry_storage_iterator operator+(const difference_type value) const noexcept {
        registry_storage_iterator copy = *this;
        return (copy += value);
    }

    constexpr registry_storage_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr registry_storage_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].first, *it[value].second};
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->first, *it->second};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const registry_storage_iterator<ILhs> &, const registry_storage_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const registry_storage_iterator<ILhs> &, const registry_storage_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const registry_storage_iterator<ILhs> &, const registry_storage_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const registry_storage_iterator<ILhs> &lhs, const registry_storage_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const registry_storage_iterator<ILhs> &lhs, const registry_storage_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const registry_storage_iterator<ILhs> &lhs, const registry_storage_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const registry_storage_iterator<ILhs> &lhs, const registry_storage_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const registry_storage_iterator<ILhs> &lhs, const registry_storage_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const registry_storage_iterator<ILhs> &lhs, const registry_storage_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const registry_storage_iterator<ILhs> &lhs, const registry_storage_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

class registry_context {
    using key_type = id_type;
    using mapped_type = basic_any<0u>;
    using container_type = dense_map<key_type, mapped_type, identity>;

public:
    template<typename Type, typename... Args>
    [[deprecated("Use ::emplace_as instead")]] Type &emplace_hint(const id_type id, Args &&...args) {
        return emplace_as<Type>(id, std::forward<Args>(args)...);
    }

    template<typename Type, typename... Args>
    Type &emplace_as(const id_type id, Args &&...args) {
        return any_cast<Type &>(ctx.try_emplace(id, std::in_place_type<Type>, std::forward<Args>(args)...).first->second);
    }

    template<typename Type, typename... Args>
    Type &emplace(Args &&...args) {
        return emplace_as<Type>(type_id<Type>().hash(), std::forward<Args>(args)...);
    }

    template<typename Type>
    Type &insert_or_assign(const id_type id, Type &&value) {
        return any_cast<std::remove_cv_t<std::remove_reference_t<Type>> &>(ctx.insert_or_assign(id, std::forward<Type>(value)).first->second);
    }

    template<typename Type>
    Type &insert_or_assign(Type &&value) {
        return insert_or_assign(type_id<Type>().hash(), std::forward<Type>(value));
    }

    template<typename Type>
    bool erase(const id_type id = type_id<Type>().hash()) {
        const auto it = ctx.find(id);
        return it != ctx.end() && it->second.type() == type_id<Type>() ? (ctx.erase(it), true) : false;
    }

    template<typename Type>
    [[deprecated("Use ::get instead")]] [[nodiscard]] const Type &at(const id_type id = type_id<Type>().hash()) const {
        return get<Type>(id);
    }

    template<typename Type>
    [[deprecated("Use ::get instead")]] [[nodiscard]] Type &at(const id_type id = type_id<Type>().hash()) {
        return get<Type>(id);
    }

    template<typename Type>
    [[nodiscard]] const Type &get(const id_type id = type_id<Type>().hash()) const {
        return any_cast<const Type &>(ctx.at(id));
    }

    template<typename Type>
    [[nodiscard]] Type &get(const id_type id = type_id<Type>().hash()) {
        return any_cast<Type &>(ctx.at(id));
    }

    template<typename Type>
    [[nodiscard]] const Type *find(const id_type id = type_id<Type>().hash()) const {
        const auto it = ctx.find(id);
        return it != ctx.cend() ? any_cast<const Type>(&it->second) : nullptr;
    }

    template<typename Type>
    [[nodiscard]] Type *find(const id_type id = type_id<Type>().hash()) {
        const auto it = ctx.find(id);
        return it != ctx.end() ? any_cast<Type>(&it->second) : nullptr;
    }

    template<typename Type>
    [[nodiscard]] bool contains(const id_type id = type_id<Type>().hash()) const {
        const auto it = ctx.find(id);
        return it != ctx.cend() && it->second.type() == type_id<Type>();
    }

private:
    container_type ctx;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Fast and reliable entity-component system.
 * @tparam Entity A valid entity type (see entt_traits for more details).
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Entity, typename Allocator>
class basic_registry {
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Entity>, "Invalid value type");
    using basic_common_type = basic_sparse_set<Entity, Allocator>;
    using entity_traits = entt_traits<Entity>;

    template<typename Type>
    using storage_for_type = typename storage_for<Type, Entity, typename alloc_traits::template rebind_alloc<std::remove_const_t<Type>>>::type;

    template<typename...>
    struct group_handler;

    template<typename... Exclude, typename... Get, typename... Owned>
    struct group_handler<exclude_t<Exclude...>, get_t<Get...>, Owned...> {
        // nasty workaround for an issue with the toolset v141 that doesn't accept a fold expression here
        static_assert(!std::disjunction_v<std::bool_constant<component_traits<Owned>::in_place_delete>...>, "Groups do not support in-place delete");
        using value_type = std::conditional_t<sizeof...(Owned) == 0, basic_common_type, std::size_t>;
        value_type current{};

        template<typename... Args>
        group_handler(Args &&...args)
            : current{std::forward<Args>(args)...} {}

        template<typename Type>
        void maybe_valid_if(basic_registry &owner, const Entity entt) {
            [[maybe_unused]] const auto cpools = std::forward_as_tuple(owner.assure<Owned>()...);

            const auto is_valid = ((std::is_same_v<Type, Owned> || std::get<storage_for_type<Owned> &>(cpools).contains(entt)) && ...)
                                  && ((std::is_same_v<Type, Get> || owner.assure<Get>().contains(entt)) && ...)
                                  && ((std::is_same_v<Type, Exclude> || !owner.assure<Exclude>().contains(entt)) && ...);

            if constexpr(sizeof...(Owned) == 0) {
                if(is_valid && !current.contains(entt)) {
                    current.emplace(entt);
                }
            } else {
                if(is_valid && !(std::get<0>(cpools).index(entt) < current)) {
                    const auto pos = current++;
                    (std::get<storage_for_type<Owned> &>(cpools).swap_elements(std::get<storage_for_type<Owned> &>(cpools).data()[pos], entt), ...);
                }
            }
        }

        void discard_if([[maybe_unused]] basic_registry &owner, const Entity entt) {
            if constexpr(sizeof...(Owned) == 0) {
                current.remove(entt);
            } else {
                if(const auto cpools = std::forward_as_tuple(owner.assure<Owned>()...); std::get<0>(cpools).contains(entt) && (std::get<0>(cpools).index(entt) < current)) {
                    const auto pos = --current;
                    (std::get<storage_for_type<Owned> &>(cpools).swap_elements(std::get<storage_for_type<Owned> &>(cpools).data()[pos], entt), ...);
                }
            }
        }
    };

    struct group_data {
        std::size_t size;
        std::shared_ptr<void> group;
        bool (*owned)(const id_type) noexcept;
        bool (*get)(const id_type) noexcept;
        bool (*exclude)(const id_type) noexcept;
    };

    template<typename Type>
    [[nodiscard]] auto &assure(const id_type id = type_hash<Type>::value()) {
        static_assert(std::is_same_v<Type, std::decay_t<Type>>, "Non-decayed types not allowed");
        auto &cpool = pools[id];

        if(!cpool) {
            cpool = std::allocate_shared<storage_for_type<std::remove_const_t<Type>>>(get_allocator(), get_allocator());
            cpool->bind(forward_as_any(*this));
        }

        ENTT_ASSERT(cpool->type() == type_id<Type>(), "Unexpected type");
        return static_cast<storage_for_type<Type> &>(*cpool);
    }

    template<typename Type>
    [[nodiscard]] const auto &assure(const id_type id = type_hash<Type>::value()) const {
        static_assert(std::is_same_v<Type, std::decay_t<Type>>, "Non-decayed types not allowed");

        if(const auto it = pools.find(id); it != pools.cend()) {
            ENTT_ASSERT(it->second->type() == type_id<Type>(), "Unexpected type");
            return static_cast<const storage_for_type<Type> &>(*it->second);
        }

        static storage_for_type<Type> placeholder{};
        return placeholder;
    }

    auto generate_identifier(const std::size_t pos) noexcept {
        ENTT_ASSERT(pos < entity_traits::to_entity(null), "No entities available");
        return entity_traits::combine(static_cast<typename entity_traits::entity_type>(pos), {});
    }

    auto recycle_identifier() noexcept {
        ENTT_ASSERT(free_list != null, "No entities available");
        const auto curr = entity_traits::to_entity(free_list);
        free_list = entity_traits::combine(entity_traits::to_integral(epool[curr]), tombstone);
        return (epool[curr] = entity_traits::combine(curr, entity_traits::to_integral(epool[curr])));
    }

    auto release_entity(const Entity entt, const typename entity_traits::version_type version) {
        const typename entity_traits::version_type vers = version + (version == entity_traits::to_version(tombstone));
        epool[entity_traits::to_entity(entt)] = entity_traits::construct(entity_traits::to_integral(free_list), vers);
        free_list = entity_traits::combine(entity_traits::to_integral(entt), tombstone);
        return vers;
    }

    void rebind() {
        for(auto &&curr: pools) {
            curr.second->bind(forward_as_any(*this));
        }
    }

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Underlying entity identifier. */
    using entity_type = Entity;
    /*! @brief Underlying version type. */
    using version_type = typename entity_traits::version_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = basic_common_type;
    /*! @brief Context type. */
    using context = internal::registry_context;

    /*! @brief Default constructor. */
    basic_registry()
        : basic_registry{allocator_type{}} {}

    /**
     * @brief Constructs an empty registry with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_registry(const allocator_type &allocator)
        : basic_registry{0u, allocator} {}

    /**
     * @brief Allocates enough memory upon construction to store `count` pools.
     * @param count The number of pools to allocate memory for.
     * @param allocator The allocator to use.
     */
    basic_registry(const size_type count, const allocator_type &allocator = allocator_type{})
        : vars{},
          free_list{tombstone},
          epool{allocator},
          pools{allocator},
          groups{allocator} {
        pools.reserve(count);
    }

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_registry(basic_registry &&other) noexcept
        : vars{std::move(other.vars)},
          free_list{std::move(other.free_list)},
          epool{std::move(other.epool)},
          pools{std::move(other.pools)},
          groups{std::move(other.groups)} {
        rebind();
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This registry.
     */
    basic_registry &operator=(basic_registry &&other) noexcept {
        vars = std::move(other.vars);
        free_list = std::move(other.free_list);
        epool = std::move(other.epool);
        pools = std::move(other.pools);
        groups = std::move(other.groups);

        rebind();

        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given registry.
     * @param other Registry to exchange the content with.
     */
    void swap(basic_registry &other) {
        using std::swap;
        swap(vars, other.vars);
        swap(free_list, other.free_list);
        swap(epool, other.epool);
        swap(pools, other.pools);
        swap(groups, other.groups);

        rebind();
        other.rebind();
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return epool.get_allocator();
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a registry.
     *
     * The iterable object returns a pair that contains the name and a reference
     * to the current storage.
     *
     * @return An iterable object to use to _visit_ the registry.
     */
    [[nodiscard]] auto storage() noexcept {
        return iterable_adaptor{internal::registry_storage_iterator{pools.begin()}, internal::registry_storage_iterator{pools.end()}};
    }

    /*! @copydoc storage */
    [[nodiscard]] auto storage() const noexcept {
        return iterable_adaptor{internal::registry_storage_iterator{pools.cbegin()}, internal::registry_storage_iterator{pools.cend()}};
    }

    /**
     * @brief Finds the storage associated with a given name, if any.
     * @param id Name used to map the storage within the registry.
     * @return A pointer to the storage if it exists, a null pointer otherwise.
     */
    [[nodiscard]] base_type *storage(const id_type id) {
        return const_cast<base_type *>(std::as_const(*this).storage(id));
    }

    /**
     * @brief Finds the storage associated with a given name, if any.
     * @param id Name used to map the storage within the registry.
     * @return A pointer to the storage if it exists, a null pointer otherwise.
     */
    [[nodiscard]] const base_type *storage(const id_type id) const {
        const auto it = pools.find(id);
        return it == pools.cend() ? nullptr : it->second.get();
    }

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Type Type of component of which to return the storage.
     * @param id Optional name used to map the storage within the registry.
     * @return The storage for the given component type.
     */
    template<typename Type>
    decltype(auto) storage(const id_type id = type_hash<Type>::value()) {
        return assure<Type>(id);
    }

    /**
     * @brief Returns the storage for a given component type.
     *
     * @warning
     * If a storage for the given component doesn't exist yet, a temporary
     * placeholder is returned instead.
     *
     * @tparam Type Type of component of which to return the storage.
     * @param id Optional name used to map the storage within the registry.
     * @return The storage for the given component type.
     */
    template<typename Type>
    decltype(auto) storage(const id_type id = type_hash<Type>::value()) const {
        return assure<Type>(id);
    }

    /**
     * @brief Returns the number of entities created so far.
     * @return Number of entities created so far.
     */
    [[nodiscard]] size_type size() const noexcept {
        return epool.size();
    }

    /**
     * @brief Returns the number of entities still in use.
     * @return Number of entities still in use.
     */
    [[nodiscard]] size_type alive() const {
        auto sz = epool.size();

        for(auto curr = free_list; curr != null; --sz) {
            curr = epool[entity_traits::to_entity(curr)];
        }

        return sz;
    }

    /**
     * @brief Increases the capacity (number of entities) of the registry.
     * @param cap Desired capacity.
     */
    void reserve(const size_type cap) {
        epool.reserve(cap);
    }

    /**
     * @brief Returns the number of entities that a registry has currently
     * allocated space for.
     * @return Capacity of the registry.
     */
    [[nodiscard]] size_type capacity() const noexcept {
        return epool.capacity();
    }

    /**
     * @brief Checks whether the registry is empty (no entities still in use).
     * @return True if the registry is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const {
        return !alive();
    }

    /**
     * @brief Direct access to the list of entities of a registry.
     *
     * The returned pointer is such that range `[data(), data() + size())` is
     * always a valid range, even if the registry is empty.
     *
     * @warning
     * This list contains both valid and destroyed entities and isn't suitable
     * for direct use.
     *
     * @return A pointer to the array of entities.
     */
    [[nodiscard]] const entity_type *data() const noexcept {
        return epool.data();
    }

    /**
     * @brief Returns the head of the list of released entities.
     *
     * This function is intended for use in conjunction with `assign`.<br/>
     * The returned entity has an invalid identifier in all cases.
     *
     * @return The head of the list of released entities.
     */
    [[nodiscard]] entity_type released() const noexcept {
        return free_list;
    }

    /**
     * @brief Checks if an identifier refers to a valid entity.
     * @param entt An identifier, either valid or not.
     * @return True if the identifier is valid, false otherwise.
     */
    [[nodiscard]] bool valid(const entity_type entt) const {
        const auto pos = size_type(entity_traits::to_entity(entt));
        return (pos < epool.size() && epool[pos] == entt);
    }

    /**
     * @brief Returns the actual version for an identifier.
     * @param entt A valid identifier.
     * @return The version for the given identifier if valid, the tombstone
     * version otherwise.
     */
    [[nodiscard]] version_type current(const entity_type entt) const {
        const auto pos = size_type(entity_traits::to_entity(entt));
        return entity_traits::to_version(pos < epool.size() ? epool[pos] : tombstone);
    }

    /**
     * @brief Creates a new entity or recycles a destroyed one.
     * @return A valid identifier.
     */
    [[nodiscard]] entity_type create() {
        return (free_list == null) ? epool.emplace_back(generate_identifier(epool.size())) : recycle_identifier();
    }

    /**
     * @copybrief create
     *
     * If the requested entity isn't in use, the suggested identifier is used.
     * Otherwise, a new identifier is generated.
     *
     * @param hint Required identifier.
     * @return A valid identifier.
     */
    [[nodiscard]] entity_type create(const entity_type hint) {
        const auto length = epool.size();

        if(hint == null || hint == tombstone) {
            return create();
        } else if(const auto req = entity_traits::to_entity(hint); !(req < length)) {
            epool.resize(size_type(req) + 1u, null);

            for(auto pos = length; pos < req; ++pos) {
                release_entity(generate_identifier(pos), {});
            }

            return (epool[req] = hint);
        } else if(const auto curr = entity_traits::to_entity(epool[req]); req == curr) {
            return create();
        } else {
            auto *it = &free_list;
            for(; entity_traits::to_entity(*it) != req; it = &epool[entity_traits::to_entity(*it)]) {}
            *it = entity_traits::combine(curr, entity_traits::to_integral(*it));
            return (epool[req] = hint);
        }
    }

    /**
     * @brief Assigns each element in a range an identifier.
     *
     * @sa create
     *
     * @tparam It Type of forward iterator.
     * @param first An iterator to the first element of the range to generate.
     * @param last An iterator past the last element of the range to generate.
     */
    template<typename It>
    void create(It first, It last) {
        for(; free_list != null && first != last; ++first) {
            *first = recycle_identifier();
        }

        const auto length = epool.size();
        epool.resize(length + std::distance(first, last), null);

        for(auto pos = length; first != last; ++first, ++pos) {
            *first = epool[pos] = generate_identifier(pos);
        }
    }

    /**
     * @brief Assigns identifiers to an empty registry.
     *
     * This function is intended for use in conjunction with `data`, `size` and
     * `released`.<br/>
     * Don't try to inject ranges of randomly generated entities nor the _wrong_
     * head for the list of destroyed entities. There is no guarantee that a
     * registry will continue to work properly in this case.
     *
     * @warning
     * There must be no entities still alive for this to work properly.
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param destroyed The head of the list of destroyed entities.
     */
    template<typename It>
    void assign(It first, It last, const entity_type destroyed) {
        ENTT_ASSERT(!alive(), "Entities still alive");
        epool.assign(first, last);
        free_list = destroyed;
    }

    /**
     * @brief Releases an identifier.
     *
     * The version is updated and the identifier can be recycled at any time.
     *
     * @warning
     * Attempting to use an invalid entity results in undefined behavior.
     *
     * @param entt A valid identifier.
     * @return The version of the recycled entity.
     */
    version_type release(const entity_type entt) {
        return release(entt, static_cast<version_type>(entity_traits::to_version(entt) + 1u));
    }

    /**
     * @brief Releases an identifier.
     *
     * The suggested version or the valid version closest to the suggested one
     * is used instead of the implicitly generated version.
     *
     * @sa release
     *
     * @param entt A valid identifier.
     * @param version A desired version upon destruction.
     * @return The version actually assigned to the entity.
     */
    version_type release(const entity_type entt, const version_type version) {
        ENTT_ASSERT(valid(entt), "Invalid identifier");
        ENTT_ASSERT(std::all_of(pools.cbegin(), pools.cend(), [entt](auto &&curr) { return (curr.second->current(entt) == entity_traits::to_version(tombstone)); }), "Non-orphan entity");
        return release_entity(entt, version);
    }

    /**
     * @brief Releases all identifiers in a range.
     *
     * @sa release
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    template<typename It>
    void release(It first, It last) {
        for(; first != last; ++first) {
            release(*first);
        }
    }

    /**
     * @brief Destroys an entity and releases its identifier.
     *
     * @sa release
     *
     * @warning
     * Adding or removing components to an entity that is being destroyed can
     * result in undefined behavior. Attempting to use an invalid entity results
     * in undefined behavior.
     *
     * @param entt A valid identifier.
     * @return The version of the recycled entity.
     */
    version_type destroy(const entity_type entt) {
        return destroy(entt, static_cast<version_type>(entity_traits::to_version(entt) + 1u));
    }

    /**
     * @brief Destroys an entity and releases its identifier.
     *
     * The suggested version or the valid version closest to the suggested one
     * is used instead of the implicitly generated version.
     *
     * @sa destroy
     *
     * @param entt A valid identifier.
     * @param version A desired version upon destruction.
     * @return The version actually assigned to the entity.
     */
    version_type destroy(const entity_type entt, const version_type version) {
        for(size_type pos = pools.size(); pos; --pos) {
            pools.begin()[pos - 1u].second->remove(entt);
        }

        return release(entt, version);
    }

    /**
     * @brief Destroys all entities in a range and releases their identifiers.
     *
     * @sa destroy
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    template<typename It>
    void destroy(It first, It last) {
        for(; first != last; ++first) {
            destroy(*first);
        }
    }

    /**
     * @brief Assigns the given component to an entity.
     *
     * The component must have a proper constructor or be of aggregate type.
     *
     * @warning
     * Attempting to assign a component to an entity that already owns it
     * results in undefined behavior.
     *
     * @tparam Type Type of component to create.
     * @tparam Args Types of arguments to use to construct the component.
     * @param entt A valid identifier.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the newly created component.
     */
    template<typename Type, typename... Args>
    decltype(auto) emplace(const entity_type entt, Args &&...args) {
        return assure<Type>().emplace(entt, std::forward<Args>(args)...);
    }

    /**
     * @brief Assigns each entity in a range the given component.
     *
     * @sa emplace
     *
     * @tparam Type Type of component to create.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param value An instance of the component to assign.
     */
    template<typename Type, typename It>
    void insert(It first, It last, const Type &value = {}) {
        assure<Type>().insert(first, last, value);
    }

    /**
     * @brief Assigns each entity in a range the given components.
     *
     * @sa emplace
     *
     * @tparam Type Type of component to create.
     * @tparam EIt Type of input iterator.
     * @tparam CIt Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param from An iterator to the first element of the range of components.
     */
    template<typename Type, typename EIt, typename CIt, typename = std::enable_if_t<std::is_same_v<typename std::iterator_traits<CIt>::value_type, Type>>>
    void insert(EIt first, EIt last, CIt from) {
        assure<Type>().insert(first, last, from);
    }

    /**
     * @brief Assigns or replaces the given component for an entity.
     *
     * @sa emplace
     * @sa replace
     *
     * @tparam Type Type of component to assign or replace.
     * @tparam Args Types of arguments to use to construct the component.
     * @param entt A valid identifier.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the newly created component.
     */
    template<typename Type, typename... Args>
    decltype(auto) emplace_or_replace(const entity_type entt, Args &&...args) {
        if(auto &cpool = assure<Type>(); cpool.contains(entt)) {
            return cpool.patch(entt, [&args...](auto &...curr) { ((curr = Type{std::forward<Args>(args)...}), ...); });
        } else {
            return cpool.emplace(entt, std::forward<Args>(args)...);
        }
    }

    /**
     * @brief Patches the given component for an entity.
     *
     * The signature of the function should be equivalent to the following:
     *
     * @code{.cpp}
     * void(Type &);
     * @endcode
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned. However, this function can be used to trigger an update signal
     * for them.
     *
     * @warning
     * Attempting to to patch a component of an entity that doesn't own it
     * results in undefined behavior.
     *
     * @tparam Type Type of component to patch.
     * @tparam Func Types of the function objects to invoke.
     * @param entt A valid identifier.
     * @param func Valid function objects.
     * @return A reference to the patched component.
     */
    template<typename Type, typename... Func>
    decltype(auto) patch(const entity_type entt, Func &&...func) {
        return assure<Type>().patch(entt, std::forward<Func>(func)...);
    }

    /**
     * @brief Replaces the given component for an entity.
     *
     * The component must have a proper constructor or be of aggregate type.
     *
     * @warning
     * Attempting to replace a component of an entity that doesn't own it
     * results in undefined behavior.
     *
     * @tparam Type Type of component to replace.
     * @tparam Args Types of arguments to use to construct the component.
     * @param entt A valid identifier.
     * @param args Parameters to use to initialize the component.
     * @return A reference to the component being replaced.
     */
    template<typename Type, typename... Args>
    decltype(auto) replace(const entity_type entt, Args &&...args) {
        return patch<Type>(entt, [&args...](auto &...curr) { ((curr = Type{std::forward<Args>(args)...}), ...); });
    }

    /**
     * @brief Removes the given components from an entity.
     *
     * @tparam Type Type of component to remove.
     * @tparam Other Other types of components to remove.
     * @param entt A valid identifier.
     * @return The number of components actually removed.
     */
    template<typename Type, typename... Other>
    size_type remove(const entity_type entt) {
        return (assure<Type>().remove(entt) + ... + assure<Other>().remove(entt));
    }

    /**
     * @brief Removes the given components from all the entities in a range.
     *
     * @sa remove
     *
     * @tparam Type Type of component to remove.
     * @tparam Other Other types of components to remove.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @return The number of components actually removed.
     */
    template<typename Type, typename... Other, typename It>
    size_type remove(It first, It last) {
        if constexpr(sizeof...(Other) == 0u) {
            return assure<Type>().remove(std::move(first), std::move(last));
        } else {
            size_type count{};

            for(auto cpools = std::forward_as_tuple(assure<Type>(), assure<Other>()...); first != last; ++first) {
                count += std::apply([entt = *first](auto &...curr) { return (curr.remove(entt) + ... + 0u); }, cpools);
            }

            return count;
        }
    }

    /**
     * @brief Erases the given components from an entity.
     *
     * @warning
     * Attempting to erase a component from an entity that doesn't own it
     * results in undefined behavior.
     *
     * @tparam Type Types of components to erase.
     * @tparam Other Other types of components to erase.
     * @param entt A valid identifier.
     */
    template<typename Type, typename... Other>
    void erase(const entity_type entt) {
        (assure<Type>().erase(entt), (assure<Other>().erase(entt), ...));
    }

    /**
     * @brief Erases the given components from all the entities in a range.
     *
     * @sa erase
     *
     * @tparam Type Types of components to erase.
     * @tparam Other Other types of components to erase.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    template<typename Type, typename... Other, typename It>
    void erase(It first, It last) {
        if constexpr(sizeof...(Other) == 0u) {
            assure<Type>().erase(std::move(first), std::move(last));
        } else {
            for(auto cpools = std::forward_as_tuple(assure<Type>(), assure<Other>()...); first != last; ++first) {
                std::apply([entt = *first](auto &...curr) { (curr.erase(entt), ...); }, cpools);
            }
        }
    }

    /**
     * @brief Removes all tombstones from a registry or only the pools for the
     * given components.
     * @tparam Type Types of components for which to clear all tombstones.
     */
    template<typename... Type>
    void compact() {
        if constexpr(sizeof...(Type) == 0) {
            for(auto &&curr: pools) {
                curr.second->compact();
            }
        } else {
            (assure<Type>().compact(), ...);
        }
    }

    /**
     * @brief Check if an entity is part of all the given storage.
     * @tparam Type Type of storage to check for.
     * @param entt A valid identifier.
     * @return True if the entity is part of all the storage, false otherwise.
     */
    template<typename... Type>
    [[nodiscard]] bool all_of(const entity_type entt) const {
        return (assure<std::remove_const_t<Type>>().contains(entt) && ...);
    }

    /**
     * @brief Check if an entity is part of at least one given storage.
     * @tparam Type Type of storage to check for.
     * @param entt A valid identifier.
     * @return True if the entity is part of at least one storage, false
     * otherwise.
     */
    template<typename... Type>
    [[nodiscard]] bool any_of(const entity_type entt) const {
        return (assure<std::remove_const_t<Type>>().contains(entt) || ...);
    }

    /**
     * @brief Returns references to the given components for an entity.
     *
     * @warning
     * Attempting to get a component from an entity that doesn't own it results
     * in undefined behavior.
     *
     * @tparam Type Types of components to get.
     * @param entt A valid identifier.
     * @return References to the components owned by the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get([[maybe_unused]] const entity_type entt) const {
        if constexpr(sizeof...(Type) == 1u) {
            return (assure<std::remove_const_t<Type>>().get(entt), ...);
        } else {
            return std::forward_as_tuple(get<Type>(entt)...);
        }
    }

    /*! @copydoc get */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get([[maybe_unused]] const entity_type entt) {
        if constexpr(sizeof...(Type) == 1u) {
            return (const_cast<Type &>(std::as_const(*this).template get<Type>(entt)), ...);
        } else {
            return std::forward_as_tuple(get<Type>(entt)...);
        }
    }

    /**
     * @brief Returns a reference to the given component for an entity.
     *
     * In case the entity doesn't own the component, the parameters provided are
     * used to construct it.
     *
     * @sa get
     * @sa emplace
     *
     * @tparam Type Type of component to get.
     * @tparam Args Types of arguments to use to construct the component.
     * @param entt A valid identifier.
     * @param args Parameters to use to initialize the component.
     * @return Reference to the component owned by the entity.
     */
    template<typename Type, typename... Args>
    [[nodiscard]] decltype(auto) get_or_emplace(const entity_type entt, Args &&...args) {
        if(auto &cpool = assure<Type>(); cpool.contains(entt)) {
            return cpool.get(entt);
        } else {
            return cpool.emplace(entt, std::forward<Args>(args)...);
        }
    }

    /**
     * @brief Returns pointers to the given components for an entity.
     *
     * @note
     * The registry retains ownership of the pointed-to components.
     *
     * @tparam Type Types of components to get.
     * @param entt A valid identifier.
     * @return Pointers to the components owned by the entity.
     */
    template<typename... Type>
    [[nodiscard]] auto try_get([[maybe_unused]] const entity_type entt) const {
        if constexpr(sizeof...(Type) == 1) {
            const auto &cpool = assure<std::remove_const_t<Type>...>();
            return cpool.contains(entt) ? std::addressof(cpool.get(entt)) : nullptr;
        } else {
            return std::make_tuple(try_get<Type>(entt)...);
        }
    }

    /*! @copydoc try_get */
    template<typename... Type>
    [[nodiscard]] auto try_get([[maybe_unused]] const entity_type entt) {
        if constexpr(sizeof...(Type) == 1) {
            return (const_cast<Type *>(std::as_const(*this).template try_get<Type>(entt)), ...);
        } else {
            return std::make_tuple(try_get<Type>(entt)...);
        }
    }

    /**
     * @brief Clears a whole registry or the pools for the given components.
     * @tparam Type Types of components to remove from their entities.
     */
    template<typename... Type>
    void clear() {
        if constexpr(sizeof...(Type) == 0) {
            for(auto &&curr: pools) {
                curr.second->clear();
            }

            each([this](const auto entity) { this->release(entity); });
        } else {
            (assure<Type>().clear(), ...);
        }
    }

    /**
     * @brief Iterates all the entities that are still in use.
     *
     * The signature of the function should be equivalent to the following:
     *
     * @code{.cpp}
     * void(const Entity);
     * @endcode
     *
     * It's not defined whether entities created during iteration are returned.
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        if(free_list == null) {
            for(auto pos = epool.size(); pos; --pos) {
                func(epool[pos - 1]);
            }
        } else {
            for(auto pos = epool.size(); pos; --pos) {
                if(const auto entity = epool[pos - 1]; entity_traits::to_entity(entity) == (pos - 1)) {
                    func(entity);
                }
            }
        }
    }

    /**
     * @brief Checks if an entity has components assigned.
     * @param entt A valid identifier.
     * @return True if the entity has no components assigned, false otherwise.
     */
    [[nodiscard]] bool orphan(const entity_type entt) const {
        return std::none_of(pools.cbegin(), pools.cend(), [entt](auto &&curr) { return curr.second->contains(entt); });
    }

    /**
     * @brief Returns a sink object for the given component.
     *
     * Use this function to receive notifications whenever a new instance of the
     * given component is created and assigned to an entity.<br/>
     * The function type for a listener is equivalent to:
     *
     * @code{.cpp}
     * void(basic_registry<Entity> &, Entity);
     * @endcode
     *
     * Listeners are invoked **after** assigning the component to the entity.
     *
     * @sa sink
     *
     * @tparam Type Type of component of which to get the sink.
     * @return A temporary sink object.
     */
    template<typename Type>
    [[nodiscard]] auto on_construct() {
        return assure<Type>().on_construct();
    }

    /**
     * @brief Returns a sink object for the given component.
     *
     * Use this function to receive notifications whenever an instance of the
     * given component is explicitly updated.<br/>
     * The function type for a listener is equivalent to:
     *
     * @code{.cpp}
     * void(basic_registry<Entity> &, Entity);
     * @endcode
     *
     * Listeners are invoked **after** updating the component.
     *
     * @sa sink
     *
     * @tparam Type Type of component of which to get the sink.
     * @return A temporary sink object.
     */
    template<typename Type>
    [[nodiscard]] auto on_update() {
        return assure<Type>().on_update();
    }

    /**
     * @brief Returns a sink object for the given component.
     *
     * Use this function to receive notifications whenever an instance of the
     * given component is removed from an entity and thus destroyed.<br/>
     * The function type for a listener is equivalent to:
     *
     * @code{.cpp}
     * void(basic_registry<Entity> &, Entity);
     * @endcode
     *
     * Listeners are invoked **before** removing the component from the entity.
     *
     * @sa sink
     *
     * @tparam Type Type of component of which to get the sink.
     * @return A temporary sink object.
     */
    template<typename Type>
    [[nodiscard]] auto on_destroy() {
        return assure<Type>().on_destroy();
    }

    /**
     * @brief Returns a view for the given components.
     *
     * Views are created on the fly and share with the registry its internal
     * data structures. Feel free to discard them after the use.<br/>
     * Creating and destroying a view is an incredibly cheap operation. As a
     * rule of thumb, storing a view should never be an option.
     *
     * @tparam Type Type of component used to construct the view.
     * @tparam Other Other types of components used to construct the view.
     * @tparam Exclude Types of components used to filter the view.
     * @return A newly created view.
     */
    template<typename Type, typename... Other, typename... Exclude>
    [[nodiscard]] basic_view<get_t<storage_for_type<const Type>, storage_for_type<const Other>...>, exclude_t<storage_for_type<const Exclude>...>>
    view(exclude_t<Exclude...> = {}) const {
        return {assure<std::remove_const_t<Type>>(), assure<std::remove_const_t<Other>>()..., assure<std::remove_const_t<Exclude>>()...};
    }

    /*! @copydoc view */
    template<typename Type, typename... Other, typename... Exclude>
    [[nodiscard]] basic_view<get_t<storage_for_type<Type>, storage_for_type<Other>...>, exclude_t<storage_for_type<Exclude>...>>
    view(exclude_t<Exclude...> = {}) {
        return {assure<std::remove_const_t<Type>>(), assure<std::remove_const_t<Other>>()..., assure<std::remove_const_t<Exclude>>()...};
    }

    /**
     * @brief Returns a group for the given components.
     *
     * Groups are created on the fly and share with the registry its internal
     * data structures. Feel free to discard them after the use.<br/>
     * Creating and destroying a group is an incredibly cheap operation. As a
     * rule of thumb, storing a group should never be an option.
     *
     * Groups support exclusion lists and can own types of components. The more
     * types are owned by a group, the faster it is to iterate entities and
     * components.<br/>
     * However, groups also affect some features of the registry such as the
     * creation and destruction of components.
     *
     * @note
     * Pools of components that are owned by a group cannot be sorted anymore.
     * The group takes the ownership of the pools and arrange components so as
     * to iterate them as fast as possible.
     *
     * @tparam Owned Type of storage _owned_ by the group.
     * @tparam Get Type of storage _observed_ by the group.
     * @tparam Exclude Type of storage used to filter the group.
     * @return A newly created group.
     */
    template<typename... Owned, typename... Get, typename... Exclude>
    [[nodiscard]] basic_group<owned_t<storage_for_type<Owned>...>, get_t<storage_for_type<Get>...>, exclude_t<storage_for_type<Exclude>...>>
    group(get_t<Get...> = {}, exclude_t<Exclude...> = {}) {
        static_assert(sizeof...(Owned) + sizeof...(Get) > 0, "Exclusion-only groups are not supported");
        static_assert(sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude) > 1, "Single component groups are not allowed");

        using handler_type = group_handler<exclude_t<std::remove_const_t<Exclude>...>, get_t<std::remove_const_t<Get>...>, std::remove_const_t<Owned>...>;

        const auto cpools = std::forward_as_tuple(assure<std::remove_const_t<Owned>>()..., assure<std::remove_const_t<Get>>()...);
        constexpr auto size = sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude);
        handler_type *handler = nullptr;

        auto it = std::find_if(groups.cbegin(), groups.cend(), [size](const auto &gdata) {
            return gdata.size == size
                   && (gdata.owned(type_hash<std::remove_const_t<Owned>>::value()) && ...)
                   && (gdata.get(type_hash<std::remove_const_t<Get>>::value()) && ...)
                   && (gdata.exclude(type_hash<std::remove_const_t<Exclude>>::value()) && ...);
        });

        if(it != groups.cend()) {
            handler = static_cast<handler_type *>(it->group.get());
        } else {
            group_data candidate = {
                size,
                std::apply([this](auto &&...args) { return std::allocate_shared<handler_type>(get_allocator(), std::forward<decltype(args)>(args)...); }, entt::uses_allocator_construction_args<typename handler_type::value_type>(get_allocator())),
                []([[maybe_unused]] const id_type ctype) noexcept { return ((ctype == type_hash<std::remove_const_t<Owned>>::value()) || ...); },
                []([[maybe_unused]] const id_type ctype) noexcept { return ((ctype == type_hash<std::remove_const_t<Get>>::value()) || ...); },
                []([[maybe_unused]] const id_type ctype) noexcept { return ((ctype == type_hash<std::remove_const_t<Exclude>>::value()) || ...); },
            };

            handler = static_cast<handler_type *>(candidate.group.get());

            const void *maybe_valid_if = nullptr;
            const void *discard_if = nullptr;

            if constexpr(sizeof...(Owned) == 0) {
                groups.push_back(std::move(candidate));
            } else {
                [[maybe_unused]] auto has_conflict = [size](const auto &gdata) {
                    const auto overlapping = (0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value()));
                    const auto sz = overlapping + (0u + ... + gdata.get(type_hash<std::remove_const_t<Get>>::value())) + (0u + ... + gdata.exclude(type_hash<std::remove_const_t<Exclude>>::value()));
                    return !overlapping || ((sz == size) || (sz == gdata.size));
                };

                ENTT_ASSERT(std::all_of(groups.cbegin(), groups.cend(), std::move(has_conflict)), "Conflicting groups");

                const auto next = std::find_if_not(groups.cbegin(), groups.cend(), [size](const auto &gdata) {
                    return !(0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value())) || (size > gdata.size);
                });

                const auto prev = std::find_if(std::make_reverse_iterator(next), groups.crend(), [](const auto &gdata) {
                    return (0u + ... + gdata.owned(type_hash<std::remove_const_t<Owned>>::value()));
                });

                maybe_valid_if = (next == groups.cend() ? maybe_valid_if : next->group.get());
                discard_if = (prev == groups.crend() ? discard_if : prev->group.get());
                groups.insert(next, std::move(candidate));
            }

            (on_construct<std::remove_const_t<Owned>>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<std::remove_const_t<Owned>>>(*handler), ...);
            (on_construct<std::remove_const_t<Get>>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<std::remove_const_t<Get>>>(*handler), ...);
            (on_destroy<std::remove_const_t<Exclude>>().before(maybe_valid_if).template connect<&handler_type::template maybe_valid_if<std::remove_const_t<Exclude>>>(*handler), ...);

            (on_destroy<std::remove_const_t<Owned>>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);
            (on_destroy<std::remove_const_t<Get>>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);
            (on_construct<std::remove_const_t<Exclude>>().before(discard_if).template connect<&handler_type::discard_if>(*handler), ...);

            if constexpr(sizeof...(Owned) == 0) {
                for(const auto entity: view<Owned..., Get...>(exclude<Exclude...>)) {
                    handler->current.emplace(entity);
                }
            } else {
                // we cannot iterate backwards because we want to leave behind valid entities in case of owned types
                for(auto *first = std::get<0>(cpools).data(), *last = first + std::get<0>(cpools).size(); first != last; ++first) {
                    handler->template maybe_valid_if<type_list_element_t<0, type_list<std::remove_const_t<Owned>...>>>(*this, *first);
                }
            }
        }

        return {handler->current, std::get<storage_for_type<std::remove_const_t<Owned>> &>(cpools)..., std::get<storage_for_type<std::remove_const_t<Get>> &>(cpools)...};
    }

    /*! @copydoc group */
    template<typename... Owned, typename... Get, typename... Exclude>
    [[nodiscard]] basic_group<owned_t<storage_for_type<const Owned>...>, get_t<storage_for_type<const Get>...>, exclude_t<storage_for_type<const Exclude>...>>
    group_if_exists(get_t<Get...> = {}, exclude_t<Exclude...> = {}) const {
        auto it = std::find_if(groups.cbegin(), groups.cend(), [](const auto &gdata) {
            return gdata.size == (sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude))
                   && (gdata.owned(type_hash<std::remove_const_t<Owned>>::value()) && ...)
                   && (gdata.get(type_hash<std::remove_const_t<Get>>::value()) && ...)
                   && (gdata.exclude(type_hash<std::remove_const_t<Exclude>>::value()) && ...);
        });

        if(it == groups.cend()) {
            return {};
        } else {
            using handler_type = group_handler<exclude_t<std::remove_const_t<Exclude>...>, get_t<std::remove_const_t<Get>...>, std::remove_const_t<Owned>...>;
            return {static_cast<handler_type *>(it->group.get())->current, assure<std::remove_const_t<Owned>>()..., assure<std::remove_const_t<Get>>()...};
        }
    }

    /**
     * @brief Checks whether the given components belong to any group.
     * @tparam Component Types of components in which one is interested.
     * @return True if the pools of the given components are _free_, false
     * otherwise.
     */
    template<typename... Type>
    [[nodiscard]] bool owned() const {
        return std::any_of(groups.cbegin(), groups.cend(), [](auto &&gdata) { return (gdata.owned(type_hash<std::remove_const_t<Type>>::value()) || ...); });
    }

    /**
     * @brief Checks whether a group can be sorted.
     * @tparam Owned Type of storage _owned_ by the group.
     * @tparam Get Type of storage _observed_ by the group.
     * @tparam Exclude Type of storage used to filter the group.
     * @return True if the group can be sorted, false otherwise.
     */
    template<typename... Owned, typename... Get, typename... Exclude>
    [[nodiscard]] bool sortable(const basic_group<owned_t<Owned...>, get_t<Get...>, exclude_t<Exclude...>> &) noexcept {
        constexpr auto size = sizeof...(Owned) + sizeof...(Get) + sizeof...(Exclude);
        auto pred = [size](const auto &gdata) { return (0u + ... + gdata.owned(type_hash<typename Owned::value_type>::value())) && (size < gdata.size); };
        return std::find_if(groups.cbegin(), groups.cend(), std::move(pred)) == groups.cend();
    }

    /**
     * @brief Sorts the elements of a given component.
     *
     * The order remains valid until a component of the given type is assigned
     * to or removed from an entity.<br/>
     * The comparison function object returns `true` if the first element is
     * _less_ than the second one, `false` otherwise. Its signature is also
     * equivalent to one of the following:
     *
     * @code{.cpp}
     * bool(const Entity, const Entity);
     * bool(const Type &, const Type &);
     * @endcode
     *
     * Moreover, it shall induce a _strict weak ordering_ on the values.<br/>
     * The sort function object offers an `operator()` that accepts:
     *
     * * An iterator to the first element of the range to sort.
     * * An iterator past the last element of the range to sort.
     * * A comparison function object to use to compare the elements.
     *
     * The comparison function object hasn't necessarily the type of the one
     * passed along with the other parameters to this member function.
     *
     * @warning
     * Pools of components owned by a group cannot be sorted.
     *
     * @tparam Type Type of components to sort.
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename Type, typename Compare, typename Sort = std_sort, typename... Args>
    void sort(Compare compare, Sort algo = Sort{}, Args &&...args) {
        ENTT_ASSERT(!owned<Type>(), "Cannot sort owned storage");
        auto &cpool = assure<Type>();

        if constexpr(std::is_invocable_v<Compare, decltype(cpool.get({})), decltype(cpool.get({}))>) {
            auto comp = [&cpool, compare = std::move(compare)](const auto lhs, const auto rhs) { return compare(std::as_const(cpool.get(lhs)), std::as_const(cpool.get(rhs))); };
            cpool.sort(std::move(comp), std::move(algo), std::forward<Args>(args)...);
        } else {
            cpool.sort(std::move(compare), std::move(algo), std::forward<Args>(args)...);
        }
    }

    /**
     * @brief Sorts two pools of components in the same way.
     *
     * Being `To` and `From` the two sets, after invoking this function an
     * iterator for `To` returns elements according to the following rules:
     *
     * * All entities in `To` that are also in `From` are returned first
     *   according to the order they have in `From`.
     * * All entities in `To` that are not in `From` are returned in no
     *   particular order after all the other entities.
     *
     * Any subsequent change to `From` won't affect the order in `To`.
     *
     * @warning
     * Pools of components owned by a group cannot be sorted.
     *
     * @tparam To Type of components to sort.
     * @tparam From Type of components to use to sort.
     */
    template<typename To, typename From>
    void sort() {
        ENTT_ASSERT(!owned<To>(), "Cannot sort owned storage");
        assure<To>().respect(assure<From>());
    }

    /**
     * @brief Returns the context object, that is, a general purpose container.
     * @return The context object, that is, a general purpose container.
     */
    context &ctx() noexcept {
        return vars;
    }

    /*! @copydoc ctx */
    const context &ctx() const noexcept {
        return vars;
    }

private:
    context vars;
    entity_type free_list;
    std::vector<entity_type, allocator_type> epool;
    // std::shared_ptr because of its type erased allocator which is useful here
    dense_map<id_type, std::shared_ptr<base_type>, identity, std::equal_to<id_type>, typename alloc_traits::template rebind_alloc<std::pair<const id_type, std::shared_ptr<base_type>>>> pools;
    std::vector<group_data, typename alloc_traits::template rebind_alloc<group_data>> groups;
};

} // namespace entt

#endif

// #include "entity/runtime_view.hpp"
#ifndef ENTT_ENTITY_RUNTIME_VIEW_HPP
#define ENTT_ENTITY_RUNTIME_VIEW_HPP

#include <algorithm>
#include <cstddef>
#include <iterator>
#include <utility>
#include <vector>
// #include "entity.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Set>
class runtime_view_iterator final {
    using iterator_type = typename Set::iterator;

    [[nodiscard]] bool valid() const {
        return (!tombstone_check || *it != tombstone)
               && std::all_of(++pools->begin(), pools->end(), [entt = *it](const auto *curr) { return curr->contains(entt); })
               && std::none_of(filter->cbegin(), filter->cend(), [entt = *it](const auto *curr) { return curr && curr->contains(entt); });
    }

public:
    using difference_type = typename iterator_type::difference_type;
    using value_type = typename iterator_type::value_type;
    using pointer = typename iterator_type::pointer;
    using reference = typename iterator_type::reference;
    using iterator_category = std::bidirectional_iterator_tag;

    constexpr runtime_view_iterator() noexcept
        : pools{},
          filter{},
          it{},
          tombstone_check{} {}

    runtime_view_iterator(const std::vector<Set *> &cpools, const std::vector<Set *> &ignore, iterator_type curr) noexcept
        : pools{&cpools},
          filter{&ignore},
          it{curr},
          tombstone_check{pools->size() == 1u && (*pools)[0u]->policy() == deletion_policy::in_place} {
        if(it != (*pools)[0]->end() && !valid()) {
            ++(*this);
        }
    }

    runtime_view_iterator &operator++() {
        while(++it != (*pools)[0]->end() && !valid()) {}
        return *this;
    }

    runtime_view_iterator operator++(int) {
        runtime_view_iterator orig = *this;
        return ++(*this), orig;
    }

    runtime_view_iterator &operator--() {
        while(--it != (*pools)[0]->begin() && !valid()) {}
        return *this;
    }

    runtime_view_iterator operator--(int) {
        runtime_view_iterator orig = *this;
        return operator--(), orig;
    }

    [[nodiscard]] pointer operator->() const noexcept {
        return it.operator->();
    }

    [[nodiscard]] reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr bool operator==(const runtime_view_iterator &other) const noexcept {
        return it == other.it;
    }

    [[nodiscard]] constexpr bool operator!=(const runtime_view_iterator &other) const noexcept {
        return !(*this == other);
    }

private:
    const std::vector<Set *> *pools;
    const std::vector<Set *> *filter;
    iterator_type it;
    bool tombstone_check;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Generic runtime view.
 *
 * Runtime views iterate over those entities that have at least all the given
 * components in their bags. During initialization, a runtime view looks at the
 * number of entities available for each component and picks up a reference to
 * the smallest set of candidate entities in order to get a performance boost
 * when iterate.<br/>
 * Order of elements during iterations are highly dependent on the order of the
 * underlying data structures. See sparse_set and its specializations for more
 * details.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New instances of the given components are created and assigned to entities.
 * * The entity currently pointed is modified (as an example, if one of the
 *   given components is removed from the entity to which the iterator points).
 * * The entity currently pointed is destroyed.
 *
 * In all the other cases, modifying the pools of the given components in any
 * way invalidates all the iterators and using them results in undefined
 * behavior.
 *
 * @note
 * Views share references to the underlying data structures of the registry that
 * generated them. Therefore any change to the entities and to the components
 * made by means of the registry are immediately reflected by the views, unless
 * a pool was missing when the view was built (in this case, the view won't
 * have a valid reference and won't be updated accordingly).
 *
 * @warning
 * Lifetime of a view must not overcome that of the registry that generated it.
 * In any other case, attempting to use a view results in undefined behavior.
 *
 * @tparam Type Common base type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Allocator>
class basic_runtime_view {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type *>, "Invalid value type");
    using container_type = std::vector<Type *, Allocator>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename Type::entity_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = Type;
    /*! @brief Bidirectional iterator type. */
    using iterator = internal::runtime_view_iterator<base_type>;

    /*! @brief Default constructor to use to create empty, invalid views. */
    basic_runtime_view() noexcept
        : basic_runtime_view{allocator_type{}} {}

    /**
     * @brief Constructs an empty, invalid view with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_runtime_view(const allocator_type &allocator)
        : pools{allocator},
          filter{allocator} {}

    /*! @brief Default copy constructor. */
    basic_runtime_view(const basic_runtime_view &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    basic_runtime_view(const basic_runtime_view &other, const allocator_type &allocator)
        : pools{other.pools, allocator},
          filter{other.filter, allocator} {}

    /*! @brief Default move constructor. */
    basic_runtime_view(basic_runtime_view &&) noexcept(std::is_nothrow_move_constructible_v<container_type>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_runtime_view(basic_runtime_view &&other, const allocator_type &allocator)
        : pools{std::move(other.pools), allocator},
          filter{std::move(other.filter), allocator} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    basic_runtime_view &operator=(const basic_runtime_view &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    basic_runtime_view &operator=(basic_runtime_view &&) noexcept(std::is_nothrow_move_assignable_v<container_type>) = default;

    /**
     * @brief Exchanges the contents with those of a given view.
     * @param other View to exchange the content with.
     */
    void swap(basic_runtime_view &other) {
        using std::swap;
        swap(pools, other.pools);
        swap(filter, other.filter);
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return pools.get_allocator();
    }

    /*! @brief Clears the view. */
    void clear() {
        pools.clear();
        filter.clear();
    }

    /**
     * @brief Appends an opaque storage object to a runtime view.
     * @param base An opaque reference to a storage object.
     * @return This runtime view.
     */
    basic_runtime_view &iterate(base_type &base) {
        if(pools.empty() || !(base.size() < pools[0u]->size())) {
            pools.push_back(&base);
        } else {
            pools.push_back(std::exchange(pools[0u], &base));
        }

        return *this;
    }

    /**
     * @brief Adds an opaque storage object as a filter of a runtime view.
     * @param base An opaque reference to a storage object.
     * @return This runtime view.
     */
    basic_runtime_view &exclude(base_type &base) {
        filter.push_back(&base);
        return *this;
    }

    /**
     * @brief Estimates the number of entities iterated by the view.
     * @return Estimated number of entities iterated by the view.
     */
    [[nodiscard]] size_type size_hint() const {
        return pools.empty() ? size_type{} : pools.front()->size();
    }

    /**
     * @brief Returns an iterator to the first entity that has the given
     * components.
     *
     * The returned iterator points to the first entity that has the given
     * components. If the view is empty, the returned iterator will be equal to
     * `end()`.
     *
     * @return An iterator to the first entity that has the given components.
     */
    [[nodiscard]] iterator begin() const {
        return pools.empty() ? iterator{} : iterator{pools, filter, pools[0]->begin()};
    }

    /**
     * @brief Returns an iterator that is past the last entity that has the
     * given components.
     *
     * The returned iterator points to the entity following the last entity that
     * has the given components. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the entity following the last entity that has the
     * given components.
     */
    [[nodiscard]] iterator end() const {
        return pools.empty() ? iterator{} : iterator{pools, filter, pools[0]->end()};
    }

    /**
     * @brief Checks if a view contains an entity.
     * @param entt A valid identifier.
     * @return True if the view contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const {
        return !pools.empty()
               && std::all_of(pools.cbegin(), pools.cend(), [entt](const auto *curr) { return curr->contains(entt); })
               && std::none_of(filter.cbegin(), filter.cend(), [entt](const auto *curr) { return curr && curr->contains(entt); });
    }

    /**
     * @brief Iterates entities and applies the given function object to them.
     *
     * The function object is invoked for each entity. It is provided only with
     * the entity itself. To get the components, users can use the registry with
     * which the view was built.<br/>
     * The signature of the function should be equivalent to the following:
     *
     * @code{.cpp}
     * void(const entity_type);
     * @endcode
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        for(const auto entity: *this) {
            func(entity);
        }
    }

private:
    container_type pools;
    container_type filter;
};

} // namespace entt

#endif

// #include "entity/snapshot.hpp"
#ifndef ENTT_ENTITY_SNAPSHOT_HPP
#define ENTT_ENTITY_SNAPSHOT_HPP

#include <array>
#include <cstddef>
#include <iterator>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../container/dense_map.hpp"

// #include "../core/type_traits.hpp"

// #include "component.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"

// #include "view.hpp"


namespace entt {

/**
 * @brief Utility class to create snapshots from a registry.
 *
 * A _snapshot_ can be either a dump of the entire registry or a narrower
 * selection of components of interest.<br/>
 * This type can be used in both cases if provided with a correctly configured
 * output archive.
 *
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class basic_snapshot {
    using entity_traits = entt_traits<typename Registry::entity_type>;

    template<typename Component, typename Archive, typename It>
    void get(Archive &archive, std::size_t sz, It first, It last) const {
        const auto view = reg->template view<const Component>();
        archive(typename entity_traits::entity_type(sz));

        while(first != last) {
            const auto entt = *(first++);

            if(reg->template all_of<Component>(entt)) {
                std::apply(archive, std::tuple_cat(std::make_tuple(entt), view.get(entt)));
            }
        }
    }

    template<typename... Component, typename Archive, typename It, std::size_t... Index>
    void component(Archive &archive, It first, It last, std::index_sequence<Index...>) const {
        std::array<std::size_t, sizeof...(Index)> size{};
        auto begin = first;

        while(begin != last) {
            const auto entt = *(begin++);
            ((reg->template all_of<Component>(entt) ? ++size[Index] : 0u), ...);
        }

        (get<Component>(archive, size[Index], first, last), ...);
    }

public:
    /*! Basic registry type. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename registry_type::entity_type;

    /**
     * @brief Constructs an instance that is bound to a given registry.
     * @param source A valid reference to a registry.
     */
    basic_snapshot(const registry_type &source) noexcept
        : reg{&source} {}

    /*! @brief Default move constructor. */
    basic_snapshot(basic_snapshot &&) noexcept = default;

    /*! @brief Default move assignment operator. @return This snapshot. */
    basic_snapshot &operator=(basic_snapshot &&) noexcept = default;

    /**
     * @brief Puts aside all the entities from the underlying registry.
     *
     * Entities are serialized along with their versions. Destroyed entities are
     * taken in consideration as well by this function.
     *
     * @tparam Archive Type of output archive.
     * @param archive A valid reference to an output archive.
     * @return An object of this type to continue creating the snapshot.
     */
    template<typename Archive>
    const basic_snapshot &entities(Archive &archive) const {
        const auto sz = reg->size();

        archive(typename entity_traits::entity_type(sz + 1u));
        archive(reg->released());

        for(auto first = reg->data(), last = first + sz; first != last; ++first) {
            archive(*first);
        }

        return *this;
    }

    /**
     * @brief Puts aside the given components.
     *
     * Each instance is serialized together with the entity to which it belongs.
     * Entities are serialized along with their versions.
     *
     * @tparam Component Types of components to serialize.
     * @tparam Archive Type of output archive.
     * @param archive A valid reference to an output archive.
     * @return An object of this type to continue creating the snapshot.
     */
    template<typename... Component, typename Archive>
    const basic_snapshot &component(Archive &archive) const {
        if constexpr(sizeof...(Component) == 1u) {
            const auto view = reg->template view<const Component...>();
            (component<Component>(archive, view.rbegin(), view.rend()), ...);
            return *this;
        } else {
            (component<Component>(archive), ...);
            return *this;
        }
    }

    /**
     * @brief Puts aside the given components for the entities in a range.
     *
     * Each instance is serialized together with the entity to which it belongs.
     * Entities are serialized along with their versions.
     *
     * @tparam Component Types of components to serialize.
     * @tparam Archive Type of output archive.
     * @tparam It Type of input iterator.
     * @param archive A valid reference to an output archive.
     * @param first An iterator to the first element of the range to serialize.
     * @param last An iterator past the last element of the range to serialize.
     * @return An object of this type to continue creating the snapshot.
     */
    template<typename... Component, typename Archive, typename It>
    const basic_snapshot &component(Archive &archive, It first, It last) const {
        component<Component...>(archive, first, last, std::index_sequence_for<Component...>{});
        return *this;
    }

private:
    const registry_type *reg;
};

/**
 * @brief Utility class to restore a snapshot as a whole.
 *
 * A snapshot loader requires that the destination registry be empty and loads
 * all the data at once while keeping intact the identifiers that the entities
 * originally had.<br/>
 * An example of use is the implementation of a save/restore utility.
 *
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class basic_snapshot_loader {
    using entity_traits = entt_traits<typename Registry::entity_type>;

    template<typename Component, typename Archive>
    void assign(Archive &archive) const {
        typename entity_traits::entity_type length{};
        entity_type entt;

        archive(length);

        if constexpr(ignore_as_empty_v<Component>) {
            while(length--) {
                archive(entt);
                const auto entity = reg->valid(entt) ? entt : reg->create(entt);
                ENTT_ASSERT(entity == entt, "Entity not available for use");
                reg->template emplace<Component>(entt);
            }
        } else {
            Component instance;

            while(length--) {
                archive(entt, instance);
                const auto entity = reg->valid(entt) ? entt : reg->create(entt);
                ENTT_ASSERT(entity == entt, "Entity not available for use");
                reg->template emplace<Component>(entt, std::move(instance));
            }
        }
    }

public:
    /*! Basic registry type. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename registry_type::entity_type;

    /**
     * @brief Constructs an instance that is bound to a given registry.
     * @param source A valid reference to a registry.
     */
    basic_snapshot_loader(registry_type &source) noexcept
        : reg{&source} {
        // restoring a snapshot as a whole requires a clean registry
        ENTT_ASSERT(reg->empty(), "Registry must be empty");
    }

    /*! @brief Default move constructor. */
    basic_snapshot_loader(basic_snapshot_loader &&) noexcept = default;

    /*! @brief Default move assignment operator. @return This loader. */
    basic_snapshot_loader &operator=(basic_snapshot_loader &&) noexcept = default;

    /**
     * @brief Restores entities that were in use during serialization.
     *
     * This function restores the entities that were in use during serialization
     * and gives them the versions they originally had.
     *
     * @tparam Archive Type of input archive.
     * @param archive A valid reference to an input archive.
     * @return A valid loader to continue restoring data.
     */
    template<typename Archive>
    const basic_snapshot_loader &entities(Archive &archive) const {
        typename entity_traits::entity_type length{};

        archive(length);
        std::vector<entity_type> all(length);

        for(std::size_t pos{}; pos < length; ++pos) {
            archive(all[pos]);
        }

        reg->assign(++all.cbegin(), all.cend(), all[0u]);

        return *this;
    }

    /**
     * @brief Restores components and assigns them to the right entities.
     *
     * The template parameter list must be exactly the same used during
     * serialization. In the event that the entity to which the component is
     * assigned doesn't exist yet, the loader will take care to create it with
     * the version it originally had.
     *
     * @tparam Component Types of components to restore.
     * @tparam Archive Type of input archive.
     * @param archive A valid reference to an input archive.
     * @return A valid loader to continue restoring data.
     */
    template<typename... Component, typename Archive>
    const basic_snapshot_loader &component(Archive &archive) const {
        (assign<Component>(archive), ...);
        return *this;
    }

    /**
     * @brief Destroys those entities that have no components.
     *
     * In case all the entities were serialized but only part of the components
     * was saved, it could happen that some of the entities have no components
     * once restored.<br/>
     * This functions helps to identify and destroy those entities.
     *
     * @return A valid loader to continue restoring data.
     */
    const basic_snapshot_loader &orphans() const {
        reg->each([this](const auto entt) {
            if(reg->orphan(entt)) {
                reg->release(entt);
            }
        });

        return *this;
    }

private:
    registry_type *reg;
};

/**
 * @brief Utility class for _continuous loading_.
 *
 * A _continuous loader_ is designed to load data from a source registry to a
 * (possibly) non-empty destination. The loader can accommodate in a registry
 * more than one snapshot in a sort of _continuous loading_ that updates the
 * destination one step at a time.<br/>
 * Identifiers that entities originally had are not transferred to the target.
 * Instead, the loader maps remote identifiers to local ones while restoring a
 * snapshot.<br/>
 * An example of use is the implementation of a client-server applications with
 * the requirement of transferring somehow parts of the representation side to
 * side.
 *
 * @tparam Registry Basic registry type.
 */
template<typename Registry>
class basic_continuous_loader {
    using entity_traits = entt_traits<typename Registry::entity_type>;

    void destroy(typename Registry::entity_type entt) {
        if(const auto it = remloc.find(entt); it == remloc.cend()) {
            const auto local = reg->create();
            remloc.emplace(entt, std::make_pair(local, true));
            reg->destroy(local);
        }
    }

    void restore(typename Registry::entity_type entt) {
        const auto it = remloc.find(entt);

        if(it == remloc.cend()) {
            const auto local = reg->create();
            remloc.emplace(entt, std::make_pair(local, true));
        } else {
            if(!reg->valid(remloc[entt].first)) {
                remloc[entt].first = reg->create();
            }

            // set the dirty flag
            remloc[entt].second = true;
        }
    }

    template<typename Container>
    auto update(int, Container &container) -> decltype(typename Container::mapped_type{}, void()) {
        // map like container
        Container other;

        for(auto &&pair: container) {
            using first_type = std::remove_const_t<typename std::decay_t<decltype(pair)>::first_type>;
            using second_type = typename std::decay_t<decltype(pair)>::second_type;

            if constexpr(std::is_same_v<first_type, entity_type> && std::is_same_v<second_type, entity_type>) {
                other.emplace(map(pair.first), map(pair.second));
            } else if constexpr(std::is_same_v<first_type, entity_type>) {
                other.emplace(map(pair.first), std::move(pair.second));
            } else {
                static_assert(std::is_same_v<second_type, entity_type>, "Neither the key nor the value are of entity type");
                other.emplace(std::move(pair.first), map(pair.second));
            }
        }

        using std::swap;
        swap(container, other);
    }

    template<typename Container>
    auto update(char, Container &container) -> decltype(typename Container::value_type{}, void()) {
        // vector like container
        static_assert(std::is_same_v<typename Container::value_type, entity_type>, "Invalid value type");

        for(auto &&entt: container) {
            entt = map(entt);
        }
    }

    template<typename Component, typename Other, typename Member>
    void update([[maybe_unused]] Component &instance, [[maybe_unused]] Member Other::*member) {
        if constexpr(!std::is_same_v<Component, Other>) {
            return;
        } else if constexpr(std::is_same_v<Member, entity_type>) {
            instance.*member = map(instance.*member);
        } else {
            // maybe a container? let's try...
            update(0, instance.*member);
        }
    }

    template<typename Component>
    void remove_if_exists() {
        for(auto &&ref: remloc) {
            const auto local = ref.second.first;

            if(reg->valid(local)) {
                reg->template remove<Component>(local);
            }
        }
    }

    template<typename Component, typename Archive, typename... Other, typename... Member>
    void assign(Archive &archive, [[maybe_unused]] Member Other::*...member) {
        typename entity_traits::entity_type length{};
        entity_type entt;

        archive(length);

        if constexpr(ignore_as_empty_v<Component>) {
            while(length--) {
                archive(entt);
                restore(entt);
                reg->template emplace_or_replace<Component>(map(entt));
            }
        } else {
            Component instance;

            while(length--) {
                archive(entt, instance);
                (update(instance, member), ...);
                restore(entt);
                reg->template emplace_or_replace<Component>(map(entt), std::move(instance));
            }
        }
    }

public:
    /*! Basic registry type. */
    using registry_type = Registry;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename registry_type::entity_type;

    /**
     * @brief Constructs an instance that is bound to a given registry.
     * @param source A valid reference to a registry.
     */
    basic_continuous_loader(registry_type &source) noexcept
        : reg{&source} {}

    /*! @brief Default move constructor. */
    basic_continuous_loader(basic_continuous_loader &&) = default;

    /*! @brief Default move assignment operator. @return This loader. */
    basic_continuous_loader &operator=(basic_continuous_loader &&) = default;

    /**
     * @brief Restores entities that were in use during serialization.
     *
     * This function restores the entities that were in use during serialization
     * and creates local counterparts for them if required.
     *
     * @tparam Archive Type of input archive.
     * @param archive A valid reference to an input archive.
     * @return A non-const reference to this loader.
     */
    template<typename Archive>
    basic_continuous_loader &entities(Archive &archive) {
        typename entity_traits::entity_type length{};
        entity_type entt{};

        archive(length);
        // discards the head of the list of destroyed entities
        archive(entt);

        for(std::size_t pos{}, last = length - 1u; pos < last; ++pos) {
            archive(entt);

            if(const auto entity = entity_traits::to_entity(entt); entity == pos) {
                restore(entt);
            } else {
                destroy(entt);
            }
        }

        return *this;
    }

    /**
     * @brief Restores components and assigns them to the right entities.
     *
     * The template parameter list must be exactly the same used during
     * serialization. In the event that the entity to which the component is
     * assigned doesn't exist yet, the loader will take care to create a local
     * counterpart for it.<br/>
     * Members can be either data members of type entity_type or containers of
     * entities. In both cases, the loader will visit them and update the
     * entities by replacing each one with its local counterpart.
     *
     * @tparam Component Type of component to restore.
     * @tparam Archive Type of input archive.
     * @tparam Other Types of components to update with local counterparts.
     * @tparam Member Types of members to update with their local counterparts.
     * @param archive A valid reference to an input archive.
     * @param member Members to update with their local counterparts.
     * @return A non-const reference to this loader.
     */
    template<typename... Component, typename Archive, typename... Other, typename... Member>
    basic_continuous_loader &component(Archive &archive, Member Other::*...member) {
        (remove_if_exists<Component>(), ...);
        (assign<Component>(archive, member...), ...);
        return *this;
    }

    /**
     * @brief Helps to purge entities that no longer have a conterpart.
     *
     * Users should invoke this member function after restoring each snapshot,
     * unless they know exactly what they are doing.
     *
     * @return A non-const reference to this loader.
     */
    basic_continuous_loader &shrink() {
        auto it = remloc.begin();

        while(it != remloc.cend()) {
            const auto local = it->second.first;
            bool &dirty = it->second.second;

            if(dirty) {
                dirty = false;
                ++it;
            } else {
                if(reg->valid(local)) {
                    reg->destroy(local);
                }

                it = remloc.erase(it);
            }
        }

        return *this;
    }

    /**
     * @brief Destroys those entities that have no components.
     *
     * In case all the entities were serialized but only part of the components
     * was saved, it could happen that some of the entities have no components
     * once restored.<br/>
     * This functions helps to identify and destroy those entities.
     *
     * @return A non-const reference to this loader.
     */
    basic_continuous_loader &orphans() {
        reg->each([this](const auto entt) {
            if(reg->orphan(entt)) {
                reg->release(entt);
            }
        });

        return *this;
    }

    /**
     * @brief Tests if a loader knows about a given entity.
     * @param entt A valid identifier.
     * @return True if `entity` is managed by the loader, false otherwise.
     */
    [[nodiscard]] bool contains(entity_type entt) const noexcept {
        return (remloc.find(entt) != remloc.cend());
    }

    /**
     * @brief Returns the identifier to which an entity refers.
     * @param entt A valid identifier.
     * @return The local identifier if any, the null entity otherwise.
     */
    [[nodiscard]] entity_type map(entity_type entt) const noexcept {
        const auto it = remloc.find(entt);
        entity_type other = null;

        if(it != remloc.cend()) {
            other = it->second.first;
        }

        return other;
    }

private:
    dense_map<entity_type, std::pair<entity_type, bool>> remloc;
    registry_type *reg;
};

} // namespace entt

#endif

// #include "entity/sparse_set.hpp"
#ifndef ENTT_ENTITY_SPARSE_SET_HPP
#define ENTT_ENTITY_SPARSE_SET_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/algorithm.hpp"

// #include "../core/any.hpp"

// #include "../core/memory.hpp"

// #include "../core/type_info.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Container>
struct sparse_set_iterator final {
    using value_type = typename Container::value_type;
    using pointer = typename Container::const_pointer;
    using reference = typename Container::const_reference;
    using difference_type = typename Container::difference_type;
    using iterator_category = std::random_access_iterator_tag;

    constexpr sparse_set_iterator() noexcept
        : packed{},
          offset{} {}

    constexpr sparse_set_iterator(const Container &ref, const difference_type idx) noexcept
        : packed{std::addressof(ref)},
          offset{idx} {}

    constexpr sparse_set_iterator &operator++() noexcept {
        return --offset, *this;
    }

    constexpr sparse_set_iterator operator++(int) noexcept {
        sparse_set_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr sparse_set_iterator &operator--() noexcept {
        return ++offset, *this;
    }

    constexpr sparse_set_iterator operator--(int) noexcept {
        sparse_set_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr sparse_set_iterator &operator+=(const difference_type value) noexcept {
        offset -= value;
        return *this;
    }

    constexpr sparse_set_iterator operator+(const difference_type value) const noexcept {
        sparse_set_iterator copy = *this;
        return (copy += value);
    }

    constexpr sparse_set_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr sparse_set_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return packed->data()[index() - value];
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return packed->data() + index();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr difference_type index() const noexcept {
        return offset - 1;
    }

private:
    const Container *packed;
    difference_type offset;
};

template<typename Type, typename Other>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return rhs.index() - lhs.index();
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator==(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator!=(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator<(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return lhs.index() > rhs.index();
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator>(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return lhs.index() < rhs.index();
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator<=(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename Type, typename Other>
[[nodiscard]] constexpr bool operator>=(const sparse_set_iterator<Type> &lhs, const sparse_set_iterator<Other> &rhs) noexcept {
    return !(lhs < rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @brief Sparse set deletion policy. */
enum class deletion_policy : std::uint8_t {
    /*! @brief Swap-and-pop deletion policy. */
    swap_and_pop = 0u,
    /*! @brief In-place deletion policy. */
    in_place = 1u
};

/**
 * @brief Basic sparse set implementation.
 *
 * Sparse set or packed array or whatever is the name users give it.<br/>
 * Two arrays: an _external_ one and an _internal_ one; a _sparse_ one and a
 * _packed_ one; one used for direct access through contiguous memory, the other
 * one used to get the data through an extra level of indirection.<br/>
 * This is largely used by the registry to offer users the fastest access ever
 * to the components. Views and groups in general are almost entirely designed
 * around sparse sets.
 *
 * This type of data structure is widely documented in the literature and on the
 * web. This is nothing more than a customized implementation suitable for the
 * purpose of the framework.
 *
 * @note
 * Internal data structures arrange elements to maximize performance. There are
 * no guarantees that entities are returned in the insertion order when iterate
 * a sparse set. Do not make assumption on the order in any case.
 *
 * @tparam Entity A valid entity type (see entt_traits for more details).
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Entity, typename Allocator>
class basic_sparse_set {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Entity>, "Invalid value type");
    using sparse_container_type = std::vector<typename alloc_traits::pointer, typename alloc_traits::template rebind_alloc<typename alloc_traits::pointer>>;
    using packed_container_type = std::vector<Entity, Allocator>;
    using entity_traits = entt_traits<Entity>;

    [[nodiscard]] auto sparse_ptr(const Entity entt) const {
        const auto pos = static_cast<size_type>(entity_traits::to_entity(entt));
        const auto page = pos / entity_traits::page_size;
        return (page < sparse.size() && sparse[page]) ? (sparse[page] + fast_mod(pos, entity_traits::page_size)) : nullptr;
    }

    [[nodiscard]] auto &sparse_ref(const Entity entt) const {
        ENTT_ASSERT(sparse_ptr(entt), "Invalid element");
        const auto pos = static_cast<size_type>(entity_traits::to_entity(entt));
        return sparse[pos / entity_traits::page_size][fast_mod(pos, entity_traits::page_size)];
    }

    [[nodiscard]] auto &assure_at_least(const Entity entt) {
        const auto pos = static_cast<size_type>(entity_traits::to_entity(entt));
        const auto page = pos / entity_traits::page_size;

        if(!(page < sparse.size())) {
            sparse.resize(page + 1u, nullptr);
        }

        if(!sparse[page]) {
            auto page_allocator{packed.get_allocator()};
            sparse[page] = alloc_traits::allocate(page_allocator, entity_traits::page_size);
            std::uninitialized_fill(sparse[page], sparse[page] + entity_traits::page_size, null);
        }

        auto &elem = sparse[page][fast_mod(pos, entity_traits::page_size)];
        ENTT_ASSERT(elem == null, "Slot not available");
        return elem;
    }

    void release_sparse_pages() {
        auto page_allocator{packed.get_allocator()};

        for(auto &&page: sparse) {
            if(page != nullptr) {
                std::destroy(page, page + entity_traits::page_size);
                alloc_traits::deallocate(page_allocator, page, entity_traits::page_size);
                page = nullptr;
            }
        }
    }

private:
    virtual const void *get_at(const std::size_t) const {
        return nullptr;
    }

    virtual void swap_at(const std::size_t, const std::size_t) {}
    virtual void move_element(const std::size_t, const std::size_t) {}

protected:
    /*! @brief Random access iterator type. */
    using basic_iterator = internal::sparse_set_iterator<packed_container_type>;

    /**
     * @brief Erases an entity from a sparse set.
     * @param it An iterator to the element to pop.
     */
    void swap_and_pop(const basic_iterator it) {
        ENTT_ASSERT(mode == deletion_policy::swap_and_pop, "Deletion policy mismatched");
        auto &self = sparse_ref(*it);
        const auto entt = entity_traits::to_entity(self);
        sparse_ref(packed.back()) = entity_traits::combine(entt, entity_traits::to_integral(packed.back()));
        packed[static_cast<size_type>(entt)] = packed.back();
        // unnecessary but it helps to detect nasty bugs
        ENTT_ASSERT((packed.back() = null, true), "");
        // lazy self-assignment guard
        self = null;
        packed.pop_back();
    }

    /**
     * @brief Erases an entity from a sparse set.
     * @param it An iterator to the element to pop.
     */
    void in_place_pop(const basic_iterator it) {
        ENTT_ASSERT(mode == deletion_policy::in_place, "Deletion policy mismatched");
        const auto entt = entity_traits::to_entity(std::exchange(sparse_ref(*it), null));
        packed[static_cast<size_type>(entt)] = std::exchange(free_list, entity_traits::combine(entt, entity_traits::reserved));
    }

protected:
    /**
     * @brief Erases entities from a sparse set.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    virtual void pop(basic_iterator first, basic_iterator last) {
        if(mode == deletion_policy::swap_and_pop) {
            for(; first != last; ++first) {
                swap_and_pop(first);
            }
        } else {
            for(; first != last; ++first) {
                in_place_pop(first);
            }
        }
    }

    /**
     * @brief Assigns an entity to a sparse set.
     * @param entt A valid identifier.
     * @param force_back Force back insertion.
     * @return Iterator pointing to the emplaced element.
     */
    virtual basic_iterator try_emplace(const Entity entt, const bool force_back, const void * = nullptr) {
        ENTT_ASSERT(!contains(entt), "Set already contains entity");

        if(auto &elem = assure_at_least(entt); free_list == null || force_back) {
            packed.push_back(entt);
            elem = entity_traits::combine(static_cast<typename entity_traits::entity_type>(packed.size() - 1u), entity_traits::to_integral(entt));
            return begin();
        } else {
            const auto pos = static_cast<size_type>(entity_traits::to_entity(free_list));
            elem = entity_traits::combine(entity_traits::to_integral(free_list), entity_traits::to_integral(entt));
            free_list = std::exchange(packed[pos], entt);
            return --(end() - pos);
        }
    }

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename entity_traits::value_type;
    /*! @brief Underlying version type. */
    using version_type = typename entity_traits::version_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Pointer type to contained entities. */
    using pointer = typename packed_container_type::const_pointer;
    /*! @brief Random access iterator type. */
    using iterator = basic_iterator;
    /*! @brief Constant random access iterator type. */
    using const_iterator = iterator;
    /*! @brief Reverse iterator type. */
    using reverse_iterator = std::reverse_iterator<iterator>;
    /*! @brief Constant reverse iterator type. */
    using const_reverse_iterator = reverse_iterator;

    /*! @brief Default constructor. */
    basic_sparse_set()
        : basic_sparse_set{type_id<void>()} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_sparse_set(const allocator_type &allocator)
        : basic_sparse_set{type_id<void>(), deletion_policy::swap_and_pop, allocator} {}

    /**
     * @brief Constructs an empty container with the given policy and allocator.
     * @param pol Type of deletion policy.
     * @param allocator The allocator to use (possibly default-constructed).
     */
    explicit basic_sparse_set(deletion_policy pol, const allocator_type &allocator = {})
        : basic_sparse_set{type_id<void>(), pol, allocator} {}

    /**
     * @brief Constructs an empty container with the given value type, policy
     * and allocator.
     * @param value Returned value type, if any.
     * @param pol Type of deletion policy.
     * @param allocator The allocator to use (possibly default-constructed).
     */
    explicit basic_sparse_set(const type_info &value, deletion_policy pol = deletion_policy::swap_and_pop, const allocator_type &allocator = {})
        : sparse{allocator},
          packed{allocator},
          info{&value},
          free_list{tombstone},
          mode{pol} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_sparse_set(basic_sparse_set &&other) noexcept
        : sparse{std::move(other.sparse)},
          packed{std::move(other.packed)},
          info{other.info},
          free_list{std::exchange(other.free_list, tombstone)},
          mode{other.mode} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_sparse_set(basic_sparse_set &&other, const allocator_type &allocator) noexcept
        : sparse{std::move(other.sparse), allocator},
          packed{std::move(other.packed), allocator},
          info{other.info},
          free_list{std::exchange(other.free_list, tombstone)},
          mode{other.mode} {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || packed.get_allocator() == other.packed.get_allocator(), "Copying a sparse set is not allowed");
    }

    /*! @brief Default destructor. */
    virtual ~basic_sparse_set() {
        release_sparse_pages();
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This sparse set.
     */
    basic_sparse_set &operator=(basic_sparse_set &&other) noexcept {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || packed.get_allocator() == other.packed.get_allocator(), "Copying a sparse set is not allowed");

        release_sparse_pages();
        sparse = std::move(other.sparse);
        packed = std::move(other.packed);
        info = other.info;
        free_list = std::exchange(other.free_list, tombstone);
        mode = other.mode;
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given sparse set.
     * @param other Sparse set to exchange the content with.
     */
    void swap(basic_sparse_set &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(info, other.info);
        swap(free_list, other.free_list);
        swap(mode, other.mode);
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return packed.get_allocator();
    }

    /**
     * @brief Returns the deletion policy of a sparse set.
     * @return The deletion policy of the sparse set.
     */
    [[nodiscard]] deletion_policy policy() const noexcept {
        return mode;
    }

    /**
     * @brief Increases the capacity of a sparse set.
     *
     * If the new capacity is greater than the current capacity, new storage is
     * allocated, otherwise the method does nothing.
     *
     * @param cap Desired capacity.
     */
    virtual void reserve(const size_type cap) {
        packed.reserve(cap);
    }

    /**
     * @brief Returns the number of elements that a sparse set has currently
     * allocated space for.
     * @return Capacity of the sparse set.
     */
    [[nodiscard]] virtual size_type capacity() const noexcept {
        return packed.capacity();
    }

    /*! @brief Requests the removal of unused capacity. */
    virtual void shrink_to_fit() {
        packed.shrink_to_fit();
    }

    /**
     * @brief Returns the extent of a sparse set.
     *
     * The extent of a sparse set is also the size of the internal sparse array.
     * There is no guarantee that the internal packed array has the same size.
     * Usually the size of the internal sparse array is equal or greater than
     * the one of the internal packed array.
     *
     * @return Extent of the sparse set.
     */
    [[nodiscard]] size_type extent() const noexcept {
        return sparse.size() * entity_traits::page_size;
    }

    /**
     * @brief Returns the number of elements in a sparse set.
     *
     * The number of elements is also the size of the internal packed array.
     * There is no guarantee that the internal sparse array has the same size.
     * Usually the size of the internal sparse array is equal or greater than
     * the one of the internal packed array.
     *
     * @return Number of elements.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.size();
    }

    /**
     * @brief Checks whether a sparse set is empty.
     * @return True if the sparse set is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.empty();
    }

    /**
     * @brief Direct access to the internal packed array.
     * @return A pointer to the internal packed array.
     */
    [[nodiscard]] pointer data() const noexcept {
        return packed.data();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first entity of the internal packed
     * array. If the sparse set is empty, the returned iterator will be equal to
     * `end()`.
     *
     * @return An iterator to the first entity of the sparse set.
     */
    [[nodiscard]] const_iterator begin() const noexcept {
        const auto pos = static_cast<typename iterator::difference_type>(packed.size());
        return iterator{packed, pos};
    }

    /*! @copydoc begin */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last entity in
     * a sparse set. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the element following the last entity of a sparse
     * set.
     */
    [[nodiscard]] iterator end() const noexcept {
        return iterator{packed, {}};
    }

    /*! @copydoc end */
    [[nodiscard]] const_iterator cend() const noexcept {
        return end();
    }

    /**
     * @brief Returns a reverse iterator to the beginning.
     *
     * The returned iterator points to the first entity of the reversed internal
     * packed array. If the sparse set is empty, the returned iterator will be
     * equal to `rend()`.
     *
     * @return An iterator to the first entity of the reversed internal packed
     * array.
     */
    [[nodiscard]] const_reverse_iterator rbegin() const noexcept {
        return std::make_reverse_iterator(end());
    }

    /*! @copydoc rbegin */
    [[nodiscard]] const_reverse_iterator crbegin() const noexcept {
        return rbegin();
    }

    /**
     * @brief Returns a reverse iterator to the end.
     *
     * The returned iterator points to the element following the last entity in
     * the reversed sparse set. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last entity of the
     * reversed sparse set.
     */
    [[nodiscard]] reverse_iterator rend() const noexcept {
        return std::make_reverse_iterator(begin());
    }

    /*! @copydoc rend */
    [[nodiscard]] const_reverse_iterator crend() const noexcept {
        return rend();
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        return contains(entt) ? --(end() - index(entt)) : end();
    }

    /**
     * @brief Checks if a sparse set contains an entity.
     * @param entt A valid identifier.
     * @return True if the sparse set contains the entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        const auto elem = sparse_ptr(entt);
        constexpr auto cap = entity_traits::to_entity(null);
        // testing versions permits to avoid accessing the packed array
        return elem && (((~cap & entity_traits::to_integral(entt)) ^ entity_traits::to_integral(*elem)) < cap);
    }

    /**
     * @brief Returns the contained version for an identifier.
     * @param entt A valid identifier.
     * @return The version for the given identifier if present, the tombstone
     * version otherwise.
     */
    [[nodiscard]] version_type current(const entity_type entt) const noexcept {
        const auto elem = sparse_ptr(entt);
        constexpr auto fallback = entity_traits::to_version(tombstone);
        return elem ? entity_traits::to_version(*elem) : fallback;
    }

    /**
     * @brief Returns the position of an entity in a sparse set.
     *
     * @warning
     * Attempting to get the position of an entity that doesn't belong to the
     * sparse set results in undefined behavior.
     *
     * @param entt A valid identifier.
     * @return The position of the entity in the sparse set.
     */
    [[nodiscard]] size_type index(const entity_type entt) const noexcept {
        ENTT_ASSERT(contains(entt), "Set does not contain entity");
        return static_cast<size_type>(entity_traits::to_entity(sparse_ref(entt)));
    }

    /**
     * @brief Returns the entity at specified location, with bounds checking.
     * @param pos The position for which to return the entity.
     * @return The entity at specified location if any, a null entity otherwise.
     */
    [[nodiscard]] entity_type at(const size_type pos) const noexcept {
        return pos < packed.size() ? packed[pos] : null;
    }

    /**
     * @brief Returns the entity at specified location, without bounds checking.
     * @param pos The position for which to return the entity.
     * @return The entity at specified location.
     */
    [[nodiscard]] entity_type operator[](const size_type pos) const noexcept {
        ENTT_ASSERT(pos < packed.size(), "Position is out of bounds");
        return packed[pos];
    }

    /**
     * @brief Returns the element assigned to an entity, if any.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the sparse set results
     * in undefined behavior.
     *
     * @param entt A valid identifier.
     * @return An opaque pointer to the element assigned to the entity, if any.
     */
    [[nodiscard]] const void *get(const entity_type entt) const noexcept {
        return get_at(index(entt));
    }

    /*! @copydoc get */
    [[nodiscard]] void *get(const entity_type entt) noexcept {
        return const_cast<void *>(std::as_const(*this).get(entt));
    }

    /**
     * @brief Assigns an entity to a sparse set.
     *
     * @warning
     * Attempting to assign an entity that already belongs to the sparse set
     * results in undefined behavior.
     *
     * @param entt A valid identifier.
     * @param value Optional opaque value to forward to mixins, if any.
     * @return Iterator pointing to the emplaced element in case of success, the
     * `end()` iterator otherwise.
     */
    iterator emplace(const entity_type entt, const void *value = nullptr) {
        return try_emplace(entt, false, value);
    }

    /**
     * @brief Bump the version number of an entity.
     *
     * @warning
     * Attempting to bump the version of an entity that doesn't belong to the
     * sparse set results in undefined behavior.
     *
     * @param entt A valid identifier.
     */
    void bump(const entity_type entt) {
        auto &entity = sparse_ref(entt);
        ENTT_ASSERT(entt != tombstone && entity != null, "Cannot set the required version");
        entity = entity_traits::combine(entity_traits::to_integral(entity), entity_traits::to_integral(entt));
        packed[static_cast<size_type>(entity_traits::to_entity(entity))] = entt;
    }

    /**
     * @brief Assigns one or more entities to a sparse set.
     *
     * @warning
     * Attempting to assign an entity that already belongs to the sparse set
     * results in undefined behavior.
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @return Iterator pointing to the first element inserted in case of
     * success, the `end()` iterator otherwise.
     */
    template<typename It>
    iterator insert(It first, It last) {
        for(auto it = first; it != last; ++it) {
            try_emplace(*it, true);
        }

        return first == last ? end() : find(*first);
    }

    /**
     * @brief Erases an entity from a sparse set.
     *
     * @warning
     * Attempting to erase an entity that doesn't belong to the sparse set
     * results in undefined behavior.
     *
     * @param entt A valid identifier.
     */
    void erase(const entity_type entt) {
        const auto it = --(end() - index(entt));
        pop(it, it + 1u);
    }

    /**
     * @brief Erases entities from a set.
     *
     * @sa erase
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    template<typename It>
    void erase(It first, It last) {
        if constexpr(std::is_same_v<It, basic_iterator>) {
            pop(first, last);
        } else {
            for(; first != last; ++first) {
                erase(*first);
            }
        }
    }

    /**
     * @brief Removes an entity from a sparse set if it exists.
     * @param entt A valid identifier.
     * @return True if the entity is actually removed, false otherwise.
     */
    bool remove(const entity_type entt) {
        return contains(entt) && (erase(entt), true);
    }

    /**
     * @brief Removes entities from a sparse set if they exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @return The number of entities actually removed.
     */
    template<typename It>
    size_type remove(It first, It last) {
        size_type count{};

        for(; first != last; ++first) {
            count += remove(*first);
        }

        return count;
    }

    /*! @brief Removes all tombstones from the packed array of a sparse set. */
    void compact() {
        size_type from = packed.size();
        for(; from && packed[from - 1u] == tombstone; --from) {}

        for(auto *it = &free_list; *it != null && from; it = std::addressof(packed[entity_traits::to_entity(*it)])) {
            if(const size_type to = entity_traits::to_entity(*it); to < from) {
                --from;
                move_element(from, to);

                using std::swap;
                swap(packed[from], packed[to]);

                const auto entity = static_cast<typename entity_traits::entity_type>(to);
                sparse_ref(packed[to]) = entity_traits::combine(entity, entity_traits::to_integral(packed[to]));
                *it = entity_traits::combine(static_cast<typename entity_traits::entity_type>(from), entity_traits::reserved);
                for(; from && packed[from - 1u] == tombstone; --from) {}
            }
        }

        free_list = tombstone;
        packed.resize(from);
    }

    /**
     * @brief Swaps two entities in a sparse set.
     *
     * For what it's worth, this function affects both the internal sparse array
     * and the internal packed array. Users should not care of that anyway.
     *
     * @warning
     * Attempting to swap entities that don't belong to the sparse set results
     * in undefined behavior.
     *
     * @param lhs A valid identifier.
     * @param rhs A valid identifier.
     */
    void swap_elements(const entity_type lhs, const entity_type rhs) {
        ENTT_ASSERT(contains(lhs) && contains(rhs), "Set does not contain entities");

        auto &entt = sparse_ref(lhs);
        auto &other = sparse_ref(rhs);

        const auto from = entity_traits::to_entity(entt);
        const auto to = entity_traits::to_entity(other);

        // basic no-leak guarantee (with invalid state) if swapping throws
        swap_at(static_cast<size_type>(from), static_cast<size_type>(to));
        entt = entity_traits::combine(to, entity_traits::to_integral(packed[from]));
        other = entity_traits::combine(from, entity_traits::to_integral(packed[to]));

        using std::swap;
        swap(packed[from], packed[to]);
    }

    /**
     * @brief Sort the first count elements according to the given comparison
     * function.
     *
     * The comparison function object must return `true` if the first element
     * is _less_ than the second one, `false` otherwise. The signature of the
     * comparison function should be equivalent to the following:
     *
     * @code{.cpp}
     * bool(const Entity, const Entity);
     * @endcode
     *
     * Moreover, the comparison function object shall induce a
     * _strict weak ordering_ on the values.
     *
     * The sort function object must offer a member function template
     * `operator()` that accepts three arguments:
     *
     * * An iterator to the first element of the range to sort.
     * * An iterator past the last element of the range to sort.
     * * A comparison function to use to compare the elements.
     *
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param length Number of elements to sort.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename Compare, typename Sort = std_sort, typename... Args>
    void sort_n(const size_type length, Compare compare, Sort algo = Sort{}, Args &&...args) {
        ENTT_ASSERT(!(length > packed.size()), "Length exceeds the number of elements");
        ENTT_ASSERT(free_list == null, "Partial sorting with tombstones is not supported");

        algo(packed.rend() - length, packed.rend(), std::move(compare), std::forward<Args>(args)...);

        for(size_type pos{}; pos < length; ++pos) {
            auto curr = pos;
            auto next = index(packed[curr]);

            while(curr != next) {
                const auto idx = index(packed[next]);
                const auto entt = packed[curr];

                swap_at(next, idx);
                const auto entity = static_cast<typename entity_traits::entity_type>(curr);
                sparse_ref(entt) = entity_traits::combine(entity, entity_traits::to_integral(packed[curr]));
                curr = std::exchange(next, idx);
            }
        }
    }

    /**
     * @brief Sort all elements according to the given comparison function.
     *
     * @sa sort_n
     *
     * @tparam Compare Type of comparison function object.
     * @tparam Sort Type of sort function object.
     * @tparam Args Types of arguments to forward to the sort function object.
     * @param compare A valid comparison function object.
     * @param algo A valid sort function object.
     * @param args Arguments to forward to the sort function object, if any.
     */
    template<typename Compare, typename Sort = std_sort, typename... Args>
    void sort(Compare compare, Sort algo = Sort{}, Args &&...args) {
        compact();
        sort_n(packed.size(), std::move(compare), std::move(algo), std::forward<Args>(args)...);
    }

    /**
     * @brief Sort entities according to their order in another sparse set.
     *
     * Entities that are part of both the sparse sets are ordered internally
     * according to the order they have in `other`. All the other entities goes
     * to the end of the list and there are no guarantees on their order.<br/>
     * In other terms, this function can be used to impose the same order on two
     * sets by using one of them as a master and the other one as a slave.
     *
     * Iterating the sparse set with a couple of iterators returns elements in
     * the expected order after a call to `respect`. See `begin` and `end` for
     * more details.
     *
     * @param other The sparse sets that imposes the order of the entities.
     */
    void respect(const basic_sparse_set &other) {
        compact();

        const auto to = other.end();
        auto from = other.begin();

        for(size_type pos = packed.size() - 1; pos && from != to; ++from) {
            if(contains(*from)) {
                if(*from != packed[pos]) {
                    // basic no-leak guarantee (with invalid state) if swapping throws
                    swap_elements(packed[pos], *from);
                }

                --pos;
            }
        }
    }

    /*! @brief Clears a sparse set. */
    void clear() {
        if(const auto last = end(); free_list == null) {
            pop(begin(), last);
        } else {
            for(auto &&entity: *this) {
                // tombstone filter on itself
                if(const auto it = find(entity); it != last) {
                    pop(it, it + 1u);
                }
            }
        }

        free_list = tombstone;
        packed.clear();
    }

    /**
     * @brief Returned value type, if any.
     * @return Returned value type, if any.
     */
    const type_info &type() const noexcept {
        return *info;
    }

    /*! @brief Forwards variables to derived classes, if any. */
    virtual void bind(any) noexcept {}

private:
    sparse_container_type sparse;
    packed_container_type packed;
    const type_info *info;
    entity_type free_list;
    deletion_policy mode;
};

} // namespace entt

#endif

// #include "entity/storage.hpp"
#ifndef ENTT_ENTITY_STORAGE_HPP
#define ENTT_ENTITY_STORAGE_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/compressed_pair.hpp"

// #include "../core/iterator.hpp"

// #include "../core/memory.hpp"

// #include "../core/type_info.hpp"

// #include "component.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"

// #include "sparse_set.hpp"

// #include "storage_mixin.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Container>
class storage_iterator final {
    friend storage_iterator<const Container>;

    using container_type = std::remove_const_t<Container>;
    using alloc_traits = std::allocator_traits<typename container_type::allocator_type>;
    using comp_traits = component_traits<std::remove_pointer_t<typename container_type::value_type>>;

    using iterator_traits = std::iterator_traits<std::conditional_t<
        std::is_const_v<Container>,
        typename alloc_traits::template rebind_traits<typename std::pointer_traits<typename container_type::value_type>::element_type>::const_pointer,
        typename alloc_traits::template rebind_traits<typename std::pointer_traits<typename container_type::value_type>::element_type>::pointer>>;

public:
    using value_type = typename iterator_traits::value_type;
    using pointer = typename iterator_traits::pointer;
    using reference = typename iterator_traits::reference;
    using difference_type = typename iterator_traits::difference_type;
    using iterator_category = std::random_access_iterator_tag;

    constexpr storage_iterator() noexcept = default;

    constexpr storage_iterator(Container *ref, const difference_type idx) noexcept
        : packed{ref},
          offset{idx} {}

    template<bool Const = std::is_const_v<Container>, typename = std::enable_if_t<Const>>
    constexpr storage_iterator(const storage_iterator<std::remove_const_t<Container>> &other) noexcept
        : storage_iterator{other.packed, other.offset} {}

    constexpr storage_iterator &operator++() noexcept {
        return --offset, *this;
    }

    constexpr storage_iterator operator++(int) noexcept {
        storage_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr storage_iterator &operator--() noexcept {
        return ++offset, *this;
    }

    constexpr storage_iterator operator--(int) noexcept {
        storage_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr storage_iterator &operator+=(const difference_type value) noexcept {
        offset -= value;
        return *this;
    }

    constexpr storage_iterator operator+(const difference_type value) const noexcept {
        storage_iterator copy = *this;
        return (copy += value);
    }

    constexpr storage_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr storage_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        const auto pos = index() - value;
        return (*packed)[pos / comp_traits::page_size][fast_mod(pos, comp_traits::page_size)];
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        const auto pos = index();
        return (*packed)[pos / comp_traits::page_size] + fast_mod(pos, comp_traits::page_size);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr difference_type index() const noexcept {
        return offset - 1;
    }

private:
    Container *packed;
    difference_type offset;
};

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return rhs.index() - lhs.index();
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator==(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator!=(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator<(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return lhs.index() > rhs.index();
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator>(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return lhs.index() < rhs.index();
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator<=(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename CLhs, typename CRhs>
[[nodiscard]] constexpr bool operator>=(const storage_iterator<CLhs> &lhs, const storage_iterator<CRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It, typename... Other>
class extended_storage_iterator final {
    template<typename Iter, typename... Args>
    friend class extended_storage_iterator;

public:
    using value_type = decltype(std::tuple_cat(std::make_tuple(*std::declval<It>()), std::forward_as_tuple(*std::declval<Other>()...)));
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr extended_storage_iterator()
        : it{} {}

    constexpr extended_storage_iterator(It base, Other... other)
        : it{base, other...} {}

    template<typename... Args, typename = std::enable_if_t<(!std::is_same_v<Other, Args> && ...) && (std::is_constructible_v<Other, Args> && ...)>>
    constexpr extended_storage_iterator(const extended_storage_iterator<It, Args...> &other)
        : it{other.it} {}

    constexpr extended_storage_iterator &operator++() noexcept {
        return ++std::get<It>(it), (++std::get<Other>(it), ...), *this;
    }

    constexpr extended_storage_iterator operator++(int) noexcept {
        extended_storage_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {*std::get<It>(it), *std::get<Other>(it)...};
    }

    template<typename... CLhs, typename... CRhs>
    friend constexpr bool operator==(const extended_storage_iterator<CLhs...> &, const extended_storage_iterator<CRhs...> &) noexcept;

private:
    std::tuple<It, Other...> it;
};

template<typename... CLhs, typename... CRhs>
[[nodiscard]] constexpr bool operator==(const extended_storage_iterator<CLhs...> &lhs, const extended_storage_iterator<CRhs...> &rhs) noexcept {
    return std::get<0>(lhs.it) == std::get<0>(rhs.it);
}

template<typename... CLhs, typename... CRhs>
[[nodiscard]] constexpr bool operator!=(const extended_storage_iterator<CLhs...> &lhs, const extended_storage_iterator<CRhs...> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic storage implementation.
 *
 * Internal data structures arrange elements to maximize performance. There are
 * no guarantees that objects are returned in the insertion order when iterate
 * a storage. Do not make assumption on the order in any case.
 *
 * @warning
 * Empty types aren't explicitly instantiated. Therefore, many of the functions
 * normally available for non-empty types will not be available for empty ones.
 *
 * @tparam Type Type of objects assigned to the entities.
 * @tparam Entity A valid entity type (see entt_traits for more details).
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Entity, typename Allocator, typename>
class basic_storage: public basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>> {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using underlying_type = basic_sparse_set<Entity, typename alloc_traits::template rebind_alloc<Entity>>;
    using container_type = std::vector<typename alloc_traits::pointer, typename alloc_traits::template rebind_alloc<typename alloc_traits::pointer>>;
    using comp_traits = component_traits<Type>;

    static constexpr bool is_pinned_type_v = !(std::is_move_constructible_v<Type> && std::is_move_assignable_v<Type>);

    [[nodiscard]] auto &element_at(const std::size_t pos) const {
        return packed.first()[pos / comp_traits::page_size][fast_mod(pos, comp_traits::page_size)];
    }

    auto assure_at_least(const std::size_t pos) {
        auto &&container = packed.first();
        const auto idx = pos / comp_traits::page_size;

        if(!(idx < container.size())) {
            auto curr = container.size();
            container.resize(idx + 1u, nullptr);

            ENTT_TRY {
                for(const auto last = container.size(); curr < last; ++curr) {
                    container[curr] = alloc_traits::allocate(packed.second(), comp_traits::page_size);
                }
            }
            ENTT_CATCH {
                container.resize(curr);
                ENTT_THROW;
            }
        }

        return container[idx] + fast_mod(pos, comp_traits::page_size);
    }

    template<typename... Args>
    auto emplace_element(const Entity entt, const bool force_back, Args &&...args) {
        const auto it = base_type::try_emplace(entt, force_back);

        ENTT_TRY {
            auto elem = assure_at_least(static_cast<size_type>(it.index()));
            entt::uninitialized_construct_using_allocator(to_address(elem), packed.second(), std::forward<Args>(args)...);
        }
        ENTT_CATCH {
            base_type::pop(it, it + 1u);
            ENTT_THROW;
        }

        return it;
    }

    void shrink_to_size(const std::size_t sz) {
        for(auto pos = sz, length = base_type::size(); pos < length; ++pos) {
            if constexpr(comp_traits::in_place_delete) {
                if(base_type::at(pos) != tombstone) {
                    std::destroy_at(std::addressof(element_at(pos)));
                }
            } else {
                std::destroy_at(std::addressof(element_at(pos)));
            }
        }

        auto &&container = packed.first();
        auto page_allocator{packed.second()};
        const auto from = (sz + comp_traits::page_size - 1u) / comp_traits::page_size;

        for(auto pos = from, last = container.size(); pos < last; ++pos) {
            alloc_traits::deallocate(page_allocator, container[pos], comp_traits::page_size);
        }

        container.resize(from);
    }

private:
    const void *get_at(const std::size_t pos) const final {
        return std::addressof(element_at(pos));
    }

    void swap_at([[maybe_unused]] const std::size_t lhs, [[maybe_unused]] const std::size_t rhs) final {
        // use a runtime value to avoid compile-time suppression that drives the code coverage tool crazy
        ENTT_ASSERT((lhs + 1u) && !is_pinned_type_v, "Pinned type");

        if constexpr(!is_pinned_type_v) {
            using std::swap;
            swap(element_at(lhs), element_at(rhs));
        }
    }

    void move_element([[maybe_unused]] const std::size_t from, [[maybe_unused]] const std::size_t to) final {
        // use a runtime value to avoid compile-time suppression that drives the code coverage tool crazy
        ENTT_ASSERT((from + 1u) && !is_pinned_type_v, "Pinned type");

        if constexpr(!is_pinned_type_v) {
            auto &elem = element_at(from);
            entt::uninitialized_construct_using_allocator(to_address(assure_at_least(to)), packed.second(), std::move(elem));
            std::destroy_at(std::addressof(elem));
        }
    }

protected:
    /*! @brief Random access iterator type. */
    using basic_iterator = typename underlying_type::basic_iterator;

    /**
     * @brief Erases entities from a sparse set.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    void pop(basic_iterator first, basic_iterator last) override {
        for(; first != last; ++first) {
            // cannot use first.index() because it would break with cross iterators
            auto &elem = element_at(base_type::index(*first));

            if constexpr(comp_traits::in_place_delete) {
                base_type::in_place_pop(first);
                std::destroy_at(std::addressof(elem));
            } else {
                auto &other = element_at(base_type::size() - 1u);
                // destroying on exit allows reentrant destructors
                [[maybe_unused]] auto unused = std::exchange(elem, std::move(other));
                std::destroy_at(std::addressof(other));
                base_type::swap_and_pop(first);
            }
        }
    }

    /**
     * @brief Assigns an entity to a storage.
     * @param entt A valid identifier.
     * @param value Optional opaque value.
     * @param force_back Force back insertion.
     * @return Iterator pointing to the emplaced element.
     */
    basic_iterator try_emplace([[maybe_unused]] const Entity entt, [[maybe_unused]] const bool force_back, const void *value) override {
        if(value) {
            if constexpr(std::is_copy_constructible_v<value_type>) {
                return emplace_element(entt, force_back, *static_cast<const value_type *>(value));
            } else {
                return base_type::end();
            }
        } else {
            if constexpr(std::is_default_constructible_v<value_type>) {
                return emplace_element(entt, force_back);
            } else {
                return base_type::end();
            }
        }
    }

public:
    /*! @brief Base type. */
    using base_type = underlying_type;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Type of the objects assigned to entities. */
    using value_type = Type;
    /*! @brief Underlying entity identifier. */
    using entity_type = Entity;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Pointer type to contained elements. */
    using pointer = typename container_type::pointer;
    /*! @brief Constant pointer type to contained elements. */
    using const_pointer = typename alloc_traits::template rebind_traits<typename alloc_traits::const_pointer>::const_pointer;
    /*! @brief Random access iterator type. */
    using iterator = internal::storage_iterator<container_type>;
    /*! @brief Constant random access iterator type. */
    using const_iterator = internal::storage_iterator<const container_type>;
    /*! @brief Reverse iterator type. */
    using reverse_iterator = std::reverse_iterator<iterator>;
    /*! @brief Constant reverse iterator type. */
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
    /*! @brief Extended iterable storage proxy. */
    using iterable = iterable_adaptor<internal::extended_storage_iterator<typename base_type::iterator, iterator>>;
    /*! @brief Constant extended iterable storage proxy. */
    using const_iterable = iterable_adaptor<internal::extended_storage_iterator<typename base_type::const_iterator, const_iterator>>;

    /*! @brief Default constructor. */
    basic_storage()
        : basic_storage{allocator_type{}} {}

    /**
     * @brief Constructs an empty storage with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_storage(const allocator_type &allocator)
        : base_type{type_id<value_type>(), deletion_policy{comp_traits::in_place_delete}, allocator},
          packed{container_type{allocator}, allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_storage(basic_storage &&other) noexcept
        : base_type{std::move(other)},
          packed{std::move(other.packed)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_storage(basic_storage &&other, const allocator_type &allocator) noexcept
        : base_type{std::move(other), allocator},
          packed{container_type{std::move(other.packed.first()), allocator}, allocator} {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || packed.second() == other.packed.second(), "Copying a storage is not allowed");
    }

    /*! @brief Default destructor. */
    ~basic_storage() override {
        shrink_to_size(0u);
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This storage.
     */
    basic_storage &operator=(basic_storage &&other) noexcept {
        ENTT_ASSERT(alloc_traits::is_always_equal::value || packed.second() == other.packed.second(), "Copying a storage is not allowed");

        shrink_to_size(0u);
        base_type::operator=(std::move(other));
        packed.first() = std::move(other.packed.first());
        propagate_on_container_move_assignment(packed.second(), other.packed.second());
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given storage.
     * @param other Storage to exchange the content with.
     */
    void swap(basic_storage &other) {
        using std::swap;
        underlying_type::swap(other);
        propagate_on_container_swap(packed.second(), other.packed.second());
        swap(packed.first(), other.packed.first());
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return allocator_type{packed.second()};
    }

    /**
     * @brief Increases the capacity of a storage.
     *
     * If the new capacity is greater than the current capacity, new storage is
     * allocated, otherwise the method does nothing.
     *
     * @param cap Desired capacity.
     */
    void reserve(const size_type cap) override {
        if(cap != 0u) {
            base_type::reserve(cap);
            assure_at_least(cap - 1u);
        }
    }

    /**
     * @brief Returns the number of elements that a storage has currently
     * allocated space for.
     * @return Capacity of the storage.
     */
    [[nodiscard]] size_type capacity() const noexcept override {
        return packed.first().size() * comp_traits::page_size;
    }

    /*! @brief Requests the removal of unused capacity. */
    void shrink_to_fit() override {
        base_type::shrink_to_fit();
        shrink_to_size(base_type::size());
    }

    /**
     * @brief Direct access to the array of objects.
     * @return A pointer to the array of objects.
     */
    [[nodiscard]] const_pointer raw() const noexcept {
        return packed.first().data();
    }

    /*! @copydoc raw */
    [[nodiscard]] pointer raw() noexcept {
        return packed.first().data();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the storage is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        const auto pos = static_cast<typename iterator::difference_type>(base_type::size());
        return const_iterator{&packed.first(), pos};
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        const auto pos = static_cast<typename iterator::difference_type>(base_type::size());
        return iterator{&packed.first(), pos};
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return const_iterator{&packed.first(), {}};
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return iterator{&packed.first(), {}};
    }

    /**
     * @brief Returns a reverse iterator to the beginning.
     *
     * The returned iterator points to the first instance of the reversed
     * internal array. If the storage is empty, the returned iterator will be
     * equal to `rend()`.
     *
     * @return An iterator to the first instance of the reversed internal array.
     */
    [[nodiscard]] const_reverse_iterator crbegin() const noexcept {
        return std::make_reverse_iterator(cend());
    }

    /*! @copydoc crbegin */
    [[nodiscard]] const_reverse_iterator rbegin() const noexcept {
        return crbegin();
    }

    /*! @copydoc rbegin */
    [[nodiscard]] reverse_iterator rbegin() noexcept {
        return std::make_reverse_iterator(end());
    }

    /**
     * @brief Returns a reverse iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the reversed internal array. Attempting to dereference the returned
     * iterator results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * reversed internal array.
     */
    [[nodiscard]] const_reverse_iterator crend() const noexcept {
        return std::make_reverse_iterator(cbegin());
    }

    /*! @copydoc crend */
    [[nodiscard]] const_reverse_iterator rend() const noexcept {
        return crend();
    }

    /*! @copydoc rend */
    [[nodiscard]] reverse_iterator rend() noexcept {
        return std::make_reverse_iterator(begin());
    }

    /**
     * @brief Returns the object assigned to an entity.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the storage results in
     * undefined behavior.
     *
     * @param entt A valid identifier.
     * @return The object assigned to the entity.
     */
    [[nodiscard]] const value_type &get(const entity_type entt) const noexcept {
        return element_at(base_type::index(entt));
    }

    /*! @copydoc get */
    [[nodiscard]] value_type &get(const entity_type entt) noexcept {
        return const_cast<value_type &>(std::as_const(*this).get(entt));
    }

    /**
     * @brief Returns the object assigned to an entity as a tuple.
     * @param entt A valid identifier.
     * @return The object assigned to the entity as a tuple.
     */
    [[nodiscard]] std::tuple<const value_type &> get_as_tuple(const entity_type entt) const noexcept {
        return std::forward_as_tuple(get(entt));
    }

    /*! @copydoc get_as_tuple */
    [[nodiscard]] std::tuple<value_type &> get_as_tuple(const entity_type entt) noexcept {
        return std::forward_as_tuple(get(entt));
    }

    /**
     * @brief Assigns an entity to a storage and constructs its object.
     *
     * @warning
     * Attempting to use an entity that already belongs to the storage results
     * in undefined behavior.
     *
     * @tparam Args Types of arguments to use to construct the object.
     * @param entt A valid identifier.
     * @param args Parameters to use to construct an object for the entity.
     * @return A reference to the newly created object.
     */
    template<typename... Args>
    value_type &emplace(const entity_type entt, Args &&...args) {
        if constexpr(std::is_aggregate_v<value_type>) {
            const auto it = emplace_element(entt, false, Type{std::forward<Args>(args)...});
            return element_at(static_cast<size_type>(it.index()));
        } else {
            const auto it = emplace_element(entt, false, std::forward<Args>(args)...);
            return element_at(static_cast<size_type>(it.index()));
        }
    }

    /**
     * @brief Updates the instance assigned to a given entity in-place.
     * @tparam Func Types of the function objects to invoke.
     * @param entt A valid identifier.
     * @param func Valid function objects.
     * @return A reference to the updated instance.
     */
    template<typename... Func>
    value_type &patch(const entity_type entt, Func &&...func) {
        const auto idx = base_type::index(entt);
        auto &elem = element_at(idx);
        (std::forward<Func>(func)(elem), ...);
        return elem;
    }

    /**
     * @brief Assigns one or more entities to a storage and constructs their
     * objects from a given instance.
     *
     * @warning
     * Attempting to assign an entity that already belongs to the storage
     * results in undefined behavior.
     *
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param value An instance of the object to construct.
     */
    template<typename It>
    void insert(It first, It last, const value_type &value = {}) {
        for(; first != last; ++first) {
            emplace_element(*first, true, value);
        }
    }

    /**
     * @brief Assigns one or more entities to a storage and constructs their
     * objects from a given range.
     *
     * @sa construct
     *
     * @tparam EIt Type of input iterator.
     * @tparam CIt Type of input iterator.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param from An iterator to the first element of the range of objects.
     */
    template<typename EIt, typename CIt, typename = std::enable_if_t<std::is_same_v<typename std::iterator_traits<CIt>::value_type, value_type>>>
    void insert(EIt first, EIt last, CIt from) {
        for(; first != last; ++first, ++from) {
            emplace_element(*first, true, *from);
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a storage.
     *
     * The iterable object returns a tuple that contains the current entity and
     * a reference to its component.
     *
     * @return An iterable object to use to _visit_ the storage.
     */
    [[nodiscard]] iterable each() noexcept {
        return {internal::extended_storage_iterator{base_type::begin(), begin()}, internal::extended_storage_iterator{base_type::end(), end()}};
    }

    /*! @copydoc each */
    [[nodiscard]] const_iterable each() const noexcept {
        return {internal::extended_storage_iterator{base_type::cbegin(), cbegin()}, internal::extended_storage_iterator{base_type::cend(), cend()}};
    }

private:
    compressed_pair<container_type, allocator_type> packed;
};

/*! @copydoc basic_storage */
template<typename Type, typename Entity, typename Allocator>
class basic_storage<Type, Entity, Allocator, std::enable_if_t<ignore_as_empty_v<Type>>>
    : public basic_sparse_set<Entity, typename std::allocator_traits<Allocator>::template rebind_alloc<Entity>> {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using underlying_type = basic_sparse_set<Entity, typename alloc_traits::template rebind_alloc<Entity>>;
    using comp_traits = component_traits<Type>;

public:
    /*! @brief Base type. */
    using base_type = underlying_type;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Type of the objects assigned to entities. */
    using value_type = Type;
    /*! @brief Underlying entity identifier. */
    using entity_type = Entity;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Extended iterable storage proxy. */
    using iterable = iterable_adaptor<internal::extended_storage_iterator<typename base_type::iterator>>;
    /*! @brief Constant extended iterable storage proxy. */
    using const_iterable = iterable_adaptor<internal::extended_storage_iterator<typename base_type::const_iterator>>;

    /*! @brief Default constructor. */
    basic_storage()
        : basic_storage{allocator_type{}} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_storage(const allocator_type &allocator)
        : base_type{type_id<value_type>(), deletion_policy{comp_traits::in_place_delete}, allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_storage(basic_storage &&other) noexcept = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_storage(basic_storage &&other, const allocator_type &allocator) noexcept
        : base_type{std::move(other), allocator} {}

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This storage.
     */
    basic_storage &operator=(basic_storage &&other) noexcept = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return allocator_type{base_type::get_allocator()};
    }

    /**
     * @brief Returns the object assigned to an entity, that is `void`.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the storage results in
     * undefined behavior.
     *
     * @param entt A valid identifier.
     */
    void get([[maybe_unused]] const entity_type entt) const noexcept {
        ENTT_ASSERT(base_type::contains(entt), "Storage does not contain entity");
    }

    /**
     * @brief Returns an empty tuple.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the storage results in
     * undefined behavior.
     *
     * @param entt A valid identifier.
     * @return Returns an empty tuple.
     */
    [[nodiscard]] std::tuple<> get_as_tuple([[maybe_unused]] const entity_type entt) const noexcept {
        ENTT_ASSERT(base_type::contains(entt), "Storage does not contain entity");
        return std::tuple{};
    }

    /**
     * @brief Assigns an entity to a storage and constructs its object.
     *
     * @warning
     * Attempting to use an entity that already belongs to the storage results
     * in undefined behavior.
     *
     * @tparam Args Types of arguments to use to construct the object.
     * @param entt A valid identifier.
     */
    template<typename... Args>
    void emplace(const entity_type entt, Args &&...) {
        base_type::try_emplace(entt, false);
    }

    /**
     * @brief Updates the instance assigned to a given entity in-place.
     * @tparam Func Types of the function objects to invoke.
     * @param entt A valid identifier.
     * @param func Valid function objects.
     */
    template<typename... Func>
    void patch([[maybe_unused]] const entity_type entt, Func &&...func) {
        ENTT_ASSERT(base_type::contains(entt), "Storage does not contain entity");
        (std::forward<Func>(func)(), ...);
    }

    /**
     * @brief Assigns entities to a storage.
     * @tparam It Type of input iterator.
     * @tparam Args Types of optional arguments.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     */
    template<typename It, typename... Args>
    void insert(It first, It last, Args &&...) {
        for(; first != last; ++first) {
            base_type::try_emplace(*first, true);
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a storage.
     *
     * The iterable object returns a tuple that contains the current entity.
     *
     * @return An iterable object to use to _visit_ the storage.
     */
    [[nodiscard]] iterable each() noexcept {
        return {internal::extended_storage_iterator{base_type::begin()}, internal::extended_storage_iterator{base_type::end()}};
    }

    /*! @copydoc each */
    [[nodiscard]] const_iterable each() const noexcept {
        return {internal::extended_storage_iterator{base_type::cbegin()}, internal::extended_storage_iterator{base_type::cend()}};
    }
};

} // namespace entt

#endif

// #include "entity/storage_mixin.hpp"
#ifndef ENTT_ENTITY_SIGH_STORAGE_MIXIN_HPP
#define ENTT_ENTITY_SIGH_STORAGE_MIXIN_HPP

#include <utility>
// #include "../config/config.h"

// #include "../core/any.hpp"

// #include "../signal/sigh.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Mixin type used to add signal support to storage types.
 *
 * The function type of a listener is equivalent to:
 *
 * @code{.cpp}
 * void(basic_registry<entity_type> &, entity_type);
 * @endcode
 *
 * This applies to all signals made available.
 *
 * @tparam Type The type of the underlying storage.
 */
template<typename Type>
class sigh_storage_mixin final: public Type {
    using basic_registry_type = basic_registry<typename Type::entity_type, typename Type::base_type::allocator_type>;
    using sigh_type = sigh<void(basic_registry_type &, const typename Type::entity_type), typename Type::allocator_type>;
    using basic_iterator = typename Type::basic_iterator;

    void pop(basic_iterator first, basic_iterator last) override {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");

        for(; first != last; ++first) {
            const auto entt = *first;
            destruction.publish(*owner, entt);
            const auto it = Type::find(entt);
            Type::pop(it, it + 1u);
        }
    }

    basic_iterator try_emplace(const typename basic_registry_type::entity_type entt, const bool force_back, const void *value) final {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");
        Type::try_emplace(entt, force_back, value);
        construction.publish(*owner, entt);
        return Type::find(entt);
    }

public:
    /*! @brief Allocator type. */
    using allocator_type = typename Type::allocator_type;
    /*! @brief Underlying entity identifier. */
    using entity_type = typename Type::entity_type;
    /*! @brief Expected registry type. */
    using registry_type = basic_registry_type;

    /*! @brief Default constructor. */
    sigh_storage_mixin()
        : sigh_storage_mixin{allocator_type{}} {}

    /**
     * @brief Constructs an empty storage with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit sigh_storage_mixin(const allocator_type &allocator)
        : Type{allocator},
          owner{},
          construction{allocator},
          destruction{allocator},
          update{allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    sigh_storage_mixin(sigh_storage_mixin &&other) noexcept
        : Type{std::move(other)},
          owner{other.owner},
          construction{std::move(other.construction)},
          destruction{std::move(other.destruction)},
          update{std::move(other.update)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    sigh_storage_mixin(sigh_storage_mixin &&other, const allocator_type &allocator) noexcept
        : Type{std::move(other), allocator},
          owner{other.owner},
          construction{std::move(other.construction), allocator},
          destruction{std::move(other.destruction), allocator},
          update{std::move(other.update), allocator} {}

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This storage.
     */
    sigh_storage_mixin &operator=(sigh_storage_mixin &&other) noexcept {
        Type::operator=(std::move(other));
        owner = other.owner;
        construction = std::move(other.construction);
        destruction = std::move(other.destruction);
        update = std::move(other.update);
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given storage.
     * @param other Storage to exchange the content with.
     */
    void swap(sigh_storage_mixin &other) {
        using std::swap;
        Type::swap(other);
        swap(owner, other.owner);
        swap(construction, other.construction);
        swap(destruction, other.destruction);
        swap(update, other.update);
    }

    /**
     * @brief Returns a sink object.
     *
     * The sink returned by this function can be used to receive notifications
     * whenever a new instance is created and assigned to an entity.<br/>
     * Listeners are invoked after the object has been assigned to the entity.
     *
     * @sa sink
     *
     * @return A temporary sink object.
     */
    [[nodiscard]] auto on_construct() noexcept {
        return sink{construction};
    }

    /**
     * @brief Returns a sink object.
     *
     * The sink returned by this function can be used to receive notifications
     * whenever an instance is explicitly updated.<br/>
     * Listeners are invoked after the object has been updated.
     *
     * @sa sink
     *
     * @return A temporary sink object.
     */
    [[nodiscard]] auto on_update() noexcept {
        return sink{update};
    }

    /**
     * @brief Returns a sink object.
     *
     * The sink returned by this function can be used to receive notifications
     * whenever an instance is removed from an entity and thus destroyed.<br/>
     * Listeners are invoked before the object has been removed from the entity.
     *
     * @sa sink
     *
     * @return A temporary sink object.
     */
    [[nodiscard]] auto on_destroy() noexcept {
        return sink{destruction};
    }

    /**
     * @brief Assigns entities to a storage.
     * @tparam Args Types of arguments to use to construct the object.
     * @param entt A valid identifier.
     * @param args Parameters to use to initialize the object.
     * @return A reference to the newly created object.
     */
    template<typename... Args>
    decltype(auto) emplace(const entity_type entt, Args &&...args) {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");
        Type::emplace(entt, std::forward<Args>(args)...);
        construction.publish(*owner, entt);
        return this->get(entt);
    }

    /**
     * @brief Patches the given instance for an entity.
     * @tparam Func Types of the function objects to invoke.
     * @param entt A valid identifier.
     * @param func Valid function objects.
     * @return A reference to the patched instance.
     */
    template<typename... Func>
    decltype(auto) patch(const entity_type entt, Func &&...func) {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");
        Type::patch(entt, std::forward<Func>(func)...);
        update.publish(*owner, entt);
        return this->get(entt);
    }

    /**
     * @brief Assigns entities to a storage.
     * @tparam It Type of input iterator.
     * @tparam Args Types of arguments to use to construct the objects assigned
     * to the entities.
     * @param first An iterator to the first element of the range of entities.
     * @param last An iterator past the last element of the range of entities.
     * @param args Parameters to use to initialize the objects assigned to the
     * entities.
     */
    template<typename It, typename... Args>
    void insert(It first, It last, Args &&...args) {
        ENTT_ASSERT(owner != nullptr, "Invalid pointer to registry");
        Type::insert(first, last, std::forward<Args>(args)...);

        for(auto it = construction.empty() ? last : first; it != last; ++it) {
            construction.publish(*owner, *it);
        }
    }

    /**
     * @brief Forwards variables to derived classes, if any.
     * @param value A variable wrapped in an opaque container.
     */
    void bind(any value) noexcept final {
        auto *reg = any_cast<basic_registry_type>(&value);
        owner = reg ? reg : owner;
        Type::bind(std::move(value));
    }

private:
    basic_registry_type *owner;
    sigh_type construction;
    sigh_type destruction;
    sigh_type update;
};

} // namespace entt

#endif

// #include "entity/view.hpp"
#ifndef ENTT_ENTITY_VIEW_HPP
#define ENTT_ENTITY_VIEW_HPP

#include <array>
#include <iterator>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/iterator.hpp"

// #include "../core/type_traits.hpp"

// #include "component.hpp"

// #include "entity.hpp"

// #include "fwd.hpp"

// #include "sparse_set.hpp"

// #include "storage.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t Get, std::size_t Exclude>
class view_iterator final {
    using iterator_type = typename Type::const_iterator;

    [[nodiscard]] bool valid() const noexcept {
        return ((Get != 0u) || (*it != tombstone))
               && std::apply([entt = *it](const auto *...curr) { return (curr->contains(entt) && ...); }, pools)
               && std::apply([entt = *it](const auto *...curr) { return (!curr->contains(entt) && ...); }, filter);
    }

public:
    using value_type = typename iterator_type::value_type;
    using pointer = typename iterator_type::pointer;
    using reference = typename iterator_type::reference;
    using difference_type = typename iterator_type::difference_type;
    using iterator_category = std::forward_iterator_tag;

    constexpr view_iterator() noexcept
        : it{},
          last{},
          pools{},
          filter{} {}

    view_iterator(iterator_type curr, iterator_type to, std::array<const Type *, Get> all_of, std::array<const Type *, Exclude> none_of) noexcept
        : it{curr},
          last{to},
          pools{all_of},
          filter{none_of} {
        while(it != last && !valid()) {
            ++it;
        }
    }

    view_iterator &operator++() noexcept {
        while(++it != last && !valid()) {}
        return *this;
    }

    view_iterator operator++(int) noexcept {
        view_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] pointer operator->() const noexcept {
        return &*it;
    }

    [[nodiscard]] reference operator*() const noexcept {
        return *operator->();
    }

    template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
    friend constexpr bool operator==(const view_iterator<LhsType, LhsArgs...> &, const view_iterator<RhsType, RhsArgs...> &) noexcept;

private:
    iterator_type it;
    iterator_type last;
    std::array<const Type *, Get> pools;
    std::array<const Type *, Exclude> filter;
};

template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
[[nodiscard]] constexpr bool operator==(const view_iterator<LhsType, LhsArgs...> &lhs, const view_iterator<RhsType, RhsArgs...> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename LhsType, auto... LhsArgs, typename RhsType, auto... RhsArgs>
[[nodiscard]] constexpr bool operator!=(const view_iterator<LhsType, LhsArgs...> &lhs, const view_iterator<RhsType, RhsArgs...> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename It, typename... Type>
struct extended_view_iterator final {
    using difference_type = std::ptrdiff_t;
    using value_type = decltype(std::tuple_cat(std::make_tuple(*std::declval<It>()), std::declval<Type>().get_as_tuple({})...));
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    constexpr extended_view_iterator()
        : it{},
          pools{} {}

    extended_view_iterator(It from, std::tuple<Type *...> storage)
        : it{from},
          pools{storage} {}

    extended_view_iterator &operator++() noexcept {
        return ++it, *this;
    }

    extended_view_iterator operator++(int) noexcept {
        extended_view_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] reference operator*() const noexcept {
        return std::apply([entt = *it](auto *...curr) { return std::tuple_cat(std::make_tuple(entt), curr->get_as_tuple(entt)...); }, pools);
    }

    [[nodiscard]] pointer operator->() const noexcept {
        return operator*();
    }

    template<typename... Lhs, typename... Rhs>
    friend bool constexpr operator==(const extended_view_iterator<Lhs...> &, const extended_view_iterator<Rhs...> &) noexcept;

private:
    It it;
    std::tuple<Type *...> pools;
};

template<typename... Lhs, typename... Rhs>
[[nodiscard]] constexpr bool operator==(const extended_view_iterator<Lhs...> &lhs, const extended_view_iterator<Rhs...> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename... Lhs, typename... Rhs>
[[nodiscard]] constexpr bool operator!=(const extended_view_iterator<Lhs...> &lhs, const extended_view_iterator<Rhs...> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief View implementation.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error, but for a few reasonable cases.
 */
template<typename, typename, typename>
class basic_view;

/**
 * @brief Multi component view.
 *
 * Multi component views iterate over those entities that are at least in the
 * given storage. During initialization, a multi component view looks at the
 * number of entities available for each component and uses the smallest set in
 * order to get a performance boost when iterating.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New elements are added to the storage.
 * * The entity currently pointed is modified (for example, components are added
 *   or removed from it).
 * * The entity currently pointed is destroyed.
 *
 * In all other cases, modifying the pools iterated by the view in any way
 * invalidates all the iterators and using them results in undefined behavior.
 *
 * @tparam Get Types of storage iterated by the view.
 * @tparam Exclude Types of storage used to filter the view.
 */
template<typename... Get, typename... Exclude>
class basic_view<get_t<Get...>, exclude_t<Exclude...>> {
    using underlying_type = std::common_type_t<typename Get::entity_type..., typename Exclude::entity_type...>;
    using basic_common_type = std::common_type_t<typename Get::base_type..., typename Exclude::base_type...>;

    template<typename, typename, typename>
    friend class basic_view;

    template<typename Type>
    static constexpr std::size_t index_of = type_list_index_v<std::remove_const_t<Type>, type_list<typename Get::value_type...>>;

    [[nodiscard]] auto opaque_check_set() const noexcept {
        std::array<const base_type *, sizeof...(Get) - 1u> other{};
        std::apply([&other, pos = 0u, view = view](const auto *...curr) mutable { ((curr == view ? void() : void(other[pos++] = curr)), ...); }, pools);
        return other;
    }

    [[nodiscard]] auto filter_as_array() const noexcept {
        return std::apply([](const auto *...curr) { return std::array<const base_type *, sizeof...(Exclude)>{curr...}; }, filter);
    }

    template<std::size_t Curr, std::size_t Other, typename... Args>
    [[nodiscard]] auto dispatch_get(const std::tuple<underlying_type, Args...> &curr) const {
        if constexpr(Curr == Other) {
            return std::forward_as_tuple(std::get<Args>(curr)...);
        } else {
            return storage<Other>().get_as_tuple(std::get<0>(curr));
        }
    }

    [[nodiscard]] auto reject(const underlying_type entt) const noexcept {
        return std::apply([entt](const auto *...curr) { return (curr->contains(entt) || ...); }, filter);
    }

    template<std::size_t Curr, typename Func, std::size_t... Index>
    void each(Func &func, std::index_sequence<Index...>) const {
        for(const auto curr: storage<Curr>().each()) {
            if(const auto entt = std::get<0>(curr); ((sizeof...(Get) != 1u) || (entt != tombstone)) && ((Curr == Index || storage<Index>().contains(entt)) && ...) && !reject(entt)) {
                if constexpr(is_applicable_v<Func, decltype(std::tuple_cat(std::tuple<entity_type>{}, std::declval<basic_view>().get({})))>) {
                    std::apply(func, std::tuple_cat(std::make_tuple(entt), dispatch_get<Curr, Index>(curr)...));
                } else {
                    std::apply(func, std::tuple_cat(dispatch_get<Curr, Index>(curr)...));
                }
            }
        }
    }

    template<typename Func, std::size_t... Index>
    void pick_and_each(Func &func, std::index_sequence<Index...> seq) const {
        ((&storage<Index>() == view ? each<Index>(func, seq) : void()), ...);
    }

public:
    /*! @brief Underlying entity identifier. */
    using entity_type = underlying_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = basic_common_type;
    /*! @brief Bidirectional iterator type. */
    using iterator = internal::view_iterator<base_type, sizeof...(Get) - 1u, sizeof...(Exclude)>;
    /*! @brief Iterable view type. */
    using iterable = iterable_adaptor<internal::extended_view_iterator<iterator, Get...>>;

    /*! @brief Default constructor to use to create empty, invalid views. */
    basic_view() noexcept
        : pools{},
          filter{},
          view{} {}

    /**
     * @brief Constructs a multi-type view from a set of storage classes.
     * @param value The storage for the types to iterate.
     * @param exclude The storage for the types used to filter the view.
     */
    basic_view(Get &...value, Exclude &...exclude) noexcept
        : pools{&value...},
          filter{&exclude...},
          view{[](const base_type *first, const auto *...other) { ((first = other->size() < first->size() ? other : first), ...); return first; }(&value...)} {}

    /**
     * @brief Constructs a multi-type view from a set of storage classes.
     * @param value The storage for the types to iterate.
     * @param excl The storage for the types used to filter the view.
     */
    basic_view(std::tuple<Get &...> value, std::tuple<Exclude &...> excl = {}) noexcept
        : pools{std::apply([](auto &...curr) { return std::make_tuple(&curr...); }, value)},
          filter{std::apply([](auto &...curr) { return std::make_tuple(&curr...); }, excl)},
          view{std::apply([](const base_type *first, const auto *...other) { ((first = other->size() < first->size() ? other : first), ...); return first; }, pools)} {}

    /**
     * @brief Creates a new view driven by a given component in its iterations.
     * @tparam Type Type of component used to drive the iteration.
     * @return A new view driven by the given component in its iterations.
     */
    template<typename Type>
    [[nodiscard]] basic_view use() const noexcept {
        return use<index_of<Type>>();
    }

    /**
     * @brief Creates a new view driven by a given component in its iterations.
     * @tparam Index Index of the component used to drive the iteration.
     * @return A new view driven by the given component in its iterations.
     */
    template<std::size_t Index>
    [[nodiscard]] basic_view use() const noexcept {
        basic_view other{*this};
        other.view = &storage<Index>();
        return other;
    }

    /**
     * @brief Updates the internal leading view if required.
     * @return A newly created and internally optimized view.
     */
    [[nodiscard]] basic_view refresh() const noexcept {
        return std::apply([](auto *...elem) { return basic_view{*elem...}; }, std::tuple_cat(pools, filter));
    }

    /**
     * @brief Returns the leading storage of a view.
     * @return The leading storage of the view.
     */
    [[nodiscard]] const base_type &handle() const noexcept {
        return *view;
    }

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Comp Type of component of which to return the storage.
     * @return The storage for the given component type.
     */
    template<typename Type>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return storage<index_of<Type>>();
    }

    /**
     * @brief Returns the storage for a given index.
     * @tparam Index Index of the storage to return.
     * @return The storage for the given index.
     */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return *std::get<Index>(pools);
    }

    /**
     * @brief Estimates the number of entities iterated by the view.
     * @return Estimated number of entities iterated by the view.
     */
    [[nodiscard]] size_type size_hint() const noexcept {
        return view->size();
    }

    /**
     * @brief Returns an iterator to the first entity of the view.
     *
     * The returned iterator points to the first entity of the view. If the view
     * is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the view.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return iterator{view->begin(), view->end(), opaque_check_set(), filter_as_array()};
    }

    /**
     * @brief Returns an iterator that is past the last entity of the view.
     *
     * The returned iterator points to the entity following the last entity of
     * the view. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the view.
     */
    [[nodiscard]] iterator end() const noexcept {
        return iterator{view->end(), view->end(), opaque_check_set(), filter_as_array()};
    }

    /**
     * @brief Returns the first entity of the view, if any.
     * @return The first entity of the view if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type front() const noexcept {
        const auto it = begin();
        return it != end() ? *it : null;
    }

    /**
     * @brief Returns the last entity of the view, if any.
     * @return The last entity of the view if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type back() const noexcept {
        auto it = view->rbegin();
        for(const auto last = view->rend(); it != last && !contains(*it); ++it) {}
        return it == view->rend() ? null : *it;
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        return contains(entt) ? iterator{view->find(entt), view->end(), opaque_check_set(), filter_as_array()} : end();
    }

    /**
     * @brief Returns the components assigned to the given entity.
     * @param entt A valid identifier.
     * @return The components assigned to the given entity.
     */
    [[nodiscard]] decltype(auto) operator[](const entity_type entt) const {
        return get(entt);
    }

    /**
     * @brief Checks if a view is properly initialized.
     * @return True if the view is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return view != nullptr;
    }

    /**
     * @brief Checks if a view contains an entity.
     * @param entt A valid identifier.
     * @return True if the view contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        return std::apply([entt](const auto *...curr) { return (curr->contains(entt) && ...); }, pools)
               && std::apply([entt](const auto *...curr) { return (!curr->contains(entt) && ...); }, filter);
    }

    /**
     * @brief Returns the components assigned to the given entity.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the view results in
     * undefined behavior.
     *
     * @tparam Type Types of components to get.
     * @param entt A valid identifier.
     * @return The components assigned to the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Type) == 0) {
            return std::apply([entt](auto *...curr) { return std::tuple_cat(curr->get_as_tuple(entt)...); }, pools);
        } else if constexpr(sizeof...(Type) == 1) {
            return (storage<index_of<Type>>().get(entt), ...);
        } else {
            return std::tuple_cat(storage<index_of<Type>>().get_as_tuple(entt)...);
        }
    }

    /**
     * @brief Returns the components assigned to the given entity.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the view results in
     * undefined behavior.
     *
     * @tparam First Index of a component to get.
     * @tparam Other Indexes of other components to get.
     * @param entt A valid identifier.
     * @return The components assigned to the entity.
     */
    template<std::size_t First, std::size_t... Other>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Other) == 0) {
            return storage<First>().get(entt);
        } else {
            return std::tuple_cat(storage<First>().get_as_tuple(entt), storage<Other>().get_as_tuple(entt)...);
        }
    }

    /**
     * @brief Iterates entities and components and applies the given function
     * object to them.
     *
     * The function object is invoked for each entity. It is provided with the
     * entity itself and a set of references to non-empty components. The
     * _constness_ of the components is as requested.<br/>
     * The signature of the function must be equivalent to one of the following
     * forms:
     *
     * @code{.cpp}
     * void(const entity_type, Type &...);
     * void(Type &...);
     * @endcode
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        pick_and_each(func, std::index_sequence_for<Get...>{});
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a view.
     *
     * The iterable object returns a tuple that contains the current entity and
     * a set of references to its non-empty components. The _constness_ of the
     * components is as requested.
     *
     * @return An iterable object to use to _visit_ the view.
     */
    [[nodiscard]] iterable each() const noexcept {
        return {internal::extended_view_iterator{begin(), pools}, internal::extended_view_iterator{end(), pools}};
    }

    /**
     * @brief Combines two views in a _more specific_ one (friend function).
     * @tparam OGet Component list of the view to combine with.
     * @tparam OExclude Filter list of the view to combine with.
     * @param other The view to combine with.
     * @return A more specific view.
     */
    template<typename... OGet, typename... OExclude>
    [[nodiscard]] auto operator|(const basic_view<get_t<OGet...>, exclude_t<OExclude...>> &other) const noexcept {
        return std::make_from_tuple<basic_view<get_t<Get..., OGet...>, exclude_t<Exclude..., OExclude...>>>(
            std::apply([](auto *...curr) { return std::forward_as_tuple(*curr...); }, std::tuple_cat(pools, other.pools, filter, other.filter)));
    }

private:
    std::tuple<Get *...> pools;
    std::tuple<Exclude *...> filter;
    const base_type *view;
};

/**
 * @brief Single component view specialization.
 *
 * Single component views are specialized in order to get a boost in terms of
 * performance. This kind of views can access the underlying data structure
 * directly and avoid superfluous checks.
 *
 * @b Important
 *
 * Iterators aren't invalidated if:
 *
 * * New elements are added to the storage.
 * * The entity currently pointed is modified (for example, components are added
 *   or removed from it).
 * * The entity currently pointed is destroyed.
 *
 * In all other cases, modifying the pool iterated by the view in any way
 * invalidates all the iterators and using them results in undefined behavior.
 *
 * @tparam Get Type of storage iterated by the view.
 */
template<typename Get>
class basic_view<get_t<Get>, exclude_t<>, std::void_t<std::enable_if_t<!component_traits<typename Get::value_type>::in_place_delete>>> {
    template<typename, typename, typename>
    friend class basic_view;

public:
    /*! @brief Underlying entity identifier. */
    using entity_type = typename Get::entity_type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Common type among all storage types. */
    using base_type = typename Get::base_type;
    /*! @brief Random access iterator type. */
    using iterator = typename base_type::iterator;
    /*! @brief Reversed iterator type. */
    using reverse_iterator = typename base_type::reverse_iterator;
    /*! @brief Iterable view type. */
    using iterable = decltype(std::declval<Get>().each());

    /*! @brief Default constructor to use to create empty, invalid views. */
    basic_view() noexcept
        : pools{},
          filter{} {}

    /**
     * @brief Constructs a single-type view from a storage class.
     * @param ref The storage for the type to iterate.
     */
    basic_view(Get &ref) noexcept
        : pools{&ref},
          filter{} {}

    /**
     * @brief Constructs a single-type view from a storage class.
     * @param ref The storage for the type to iterate.
     */
    basic_view(std::tuple<Get &> ref, std::tuple<> = {}) noexcept
        : pools{&std::get<0>(ref)},
          filter{} {}

    /**
     * @brief Returns the leading storage of a view.
     * @return The leading storage of the view.
     */
    [[nodiscard]] const base_type &handle() const noexcept {
        return storage();
    }

    /**
     * @brief Returns the storage for a given component type.
     * @tparam Type Type of component of which to return the storage.
     * @return The storage for the given component type.
     */
    template<typename Type = typename Get::value_type>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        static_assert(std::is_same_v<std::remove_const_t<Type>, typename Get::value_type>, "Invalid component type");
        return storage<0>();
    }

    /**
     * @brief Returns the storage for a given index.
     * @tparam Index Index of the storage to return.
     * @return The storage for the given index.
     */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) storage() const noexcept {
        return *std::get<Index>(pools);
    }

    /**
     * @brief Returns the number of entities that have the given component.
     * @return Number of entities that have the given component.
     */
    [[nodiscard]] size_type size() const noexcept {
        return handle().size();
    }

    /**
     * @brief Checks whether a view is empty.
     * @return True if the view is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return handle().empty();
    }

    /**
     * @brief Returns an iterator to the first entity of the view.
     *
     * The returned iterator points to the first entity of the view. If the view
     * is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first entity of the view.
     */
    [[nodiscard]] iterator begin() const noexcept {
        return handle().begin();
    }

    /**
     * @brief Returns an iterator that is past the last entity of the view.
     *
     * The returned iterator points to the entity following the last entity of
     * the view. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the view.
     */
    [[nodiscard]] iterator end() const noexcept {
        return handle().end();
    }

    /**
     * @brief Returns an iterator to the first entity of the reversed view.
     *
     * The returned iterator points to the first entity of the reversed view. If
     * the view is empty, the returned iterator will be equal to `rend()`.
     *
     * @return An iterator to the first entity of the reversed view.
     */
    [[nodiscard]] reverse_iterator rbegin() const noexcept {
        return handle().rbegin();
    }

    /**
     * @brief Returns an iterator that is past the last entity of the reversed
     * view.
     *
     * The returned iterator points to the entity following the last entity of
     * the reversed view. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the entity following the last entity of the
     * reversed view.
     */
    [[nodiscard]] reverse_iterator rend() const noexcept {
        return handle().rend();
    }

    /**
     * @brief Returns the first entity of the view, if any.
     * @return The first entity of the view if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type front() const noexcept {
        return empty() ? null : *begin();
    }

    /**
     * @brief Returns the last entity of the view, if any.
     * @return The last entity of the view if one exists, the null entity
     * otherwise.
     */
    [[nodiscard]] entity_type back() const noexcept {
        return empty() ? null : *rbegin();
    }

    /**
     * @brief Finds an entity.
     * @param entt A valid identifier.
     * @return An iterator to the given entity if it's found, past the end
     * iterator otherwise.
     */
    [[nodiscard]] iterator find(const entity_type entt) const noexcept {
        return contains(entt) ? handle().find(entt) : end();
    }

    /**
     * @brief Returns the identifier that occupies the given position.
     * @param pos Position of the element to return.
     * @return The identifier that occupies the given position.
     */
    [[nodiscard]] entity_type operator[](const size_type pos) const {
        return begin()[pos];
    }

    /**
     * @brief Returns the component assigned to the given entity.
     * @param entt A valid identifier.
     * @return The component assigned to the given entity.
     */
    [[nodiscard]] decltype(auto) operator[](const entity_type entt) const {
        return storage().get(entt);
    }

    /**
     * @brief Checks if a view is properly initialized.
     * @return True if the view is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return std::get<0>(pools) != nullptr;
    }

    /**
     * @brief Checks if a view contains an entity.
     * @param entt A valid identifier.
     * @return True if the view contains the given entity, false otherwise.
     */
    [[nodiscard]] bool contains(const entity_type entt) const noexcept {
        return handle().contains(entt);
    }

    /**
     * @brief Returns the component assigned to the given entity.
     *
     * @warning
     * Attempting to use an entity that doesn't belong to the view results in
     * undefined behavior.
     *
     * @tparam Type Type or index of the component to get.
     * @param entt A valid identifier.
     * @return The component assigned to the entity.
     */
    template<typename... Type>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        if constexpr(sizeof...(Type) == 0) {
            return storage().get_as_tuple(entt);
        } else {
            static_assert((std::is_same_v<std::remove_const_t<Type>, typename Get::value_type> && ...), "Invalid component type");
            return storage().get(entt);
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    [[nodiscard]] decltype(auto) get(const entity_type entt) const {
        return storage().get(entt);
    }

    /**
     * @brief Iterates entities and components and applies the given function
     * object to them.
     *
     * The function object is invoked for each entity. It is provided with the
     * entity itself and a reference to the component if it's a non-empty one.
     * The _constness_ of the component is as requested.<br/>
     * The signature of the function must be equivalent to one of the following
     * forms:
     *
     * @code{.cpp}
     * void(const entity_type, Type &);
     * void(typename Type &);
     * @endcode
     *
     * @note
     * Empty types aren't explicitly instantiated and therefore they are never
     * returned during iterations.
     *
     * @tparam Func Type of the function object to invoke.
     * @param func A valid function object.
     */
    template<typename Func>
    void each(Func func) const {
        if constexpr(is_applicable_v<Func, decltype(*each().begin())>) {
            for(const auto pack: each()) {
                std::apply(func, pack);
            }
        } else if constexpr(ignore_as_empty_v<typename Get::value_type>) {
            for(size_type pos{}, last = size(); pos < last; ++pos) {
                func();
            }
        } else {
            for(auto &&component: storage()) {
                func(component);
            }
        }
    }

    /**
     * @brief Returns an iterable object to use to _visit_ a view.
     *
     * The iterable object returns a tuple that contains the current entity and
     * a reference to its component if it's a non-empty one. The _constness_ of
     * the component is as requested.
     *
     * @return An iterable object to use to _visit_ the view.
     */
    [[nodiscard]] iterable each() const noexcept {
        return storage().each();
    }

    /**
     * @brief Combines two views in a _more specific_ one (friend function).
     * @tparam OGet Component list of the view to combine with.
     * @tparam OExclude Filter list of the view to combine with.
     * @param other The view to combine with.
     * @return A more specific view.
     */
    template<typename... OGet, typename... OExclude>
    [[nodiscard]] auto operator|(const basic_view<get_t<OGet...>, exclude_t<OExclude...>> &other) const noexcept {
        return std::make_from_tuple<basic_view<get_t<Get, OGet...>, exclude_t<OExclude...>>>(
            std::apply([](auto *...curr) { return std::forward_as_tuple(*curr...); }, std::tuple_cat(pools, other.pools, other.filter)));
    }

private:
    std::tuple<Get *> pools;
    std::tuple<> filter;
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of storage classes used to create the view.
 * @param storage The storage for the types to iterate.
 */
template<typename... Type>
basic_view(Type &...storage) -> basic_view<get_t<Type...>, exclude_t<>>;

/**
 * @brief Deduction guide.
 * @tparam Get Types of components iterated by the view.
 * @tparam Exclude Types of components used to filter the view.
 */
template<typename... Get, typename... Exclude>
basic_view(std::tuple<Get &...>, std::tuple<Exclude &...> = {}) -> basic_view<get_t<Get...>, exclude_t<Exclude...>>;

} // namespace entt

#endif

// #include "graph/adjacency_matrix.hpp"
#ifndef ENTT_GRAPH_ADJACENCY_MATRIX_HPP
#define ENTT_GRAPH_ADJACENCY_MATRIX_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_GRAPH_FWD_HPP
#define ENTT_GRAPH_FWD_HPP

#include <cstddef>
#include <memory>
// #include "../core/fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/*! @brief Undirected graph category tag. */
struct directed_tag {};

/*! @brief Directed graph category tag. */
struct undirected_tag: directed_tag {};

template<typename, typename = std::allocator<std::size_t>>
class adjacency_matrix;

template<typename = std::allocator<id_type>>
class basic_flow;

/*! @brief Alias declaration for the most common use case. */
using flow = basic_flow<>;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class edge_iterator {
    using size_type = std::size_t;

public:
    using value_type = std::pair<size_type, size_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr edge_iterator() noexcept
        : it{},
          vert{},
          pos{},
          last{},
          offset{} {}

    constexpr edge_iterator(It base, const size_type vertices, const size_type from, const size_type to, const size_type step) noexcept
        : it{std::move(base)},
          vert{vertices},
          pos{from},
          last{to},
          offset{step} {
        for(; pos != last && !it[pos]; pos += offset) {}
    }

    constexpr edge_iterator &operator++() noexcept {
        for(pos += offset; pos != last && !it[pos]; pos += offset) {}
        return *this;
    }

    constexpr edge_iterator operator++(int) noexcept {
        edge_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::make_pair<size_type>(pos / vert, pos % vert);
    }

    template<typename Type>
    friend constexpr bool operator==(const edge_iterator<Type> &, const edge_iterator<Type> &) noexcept;

private:
    It it;
    size_type vert;
    size_type pos;
    size_type last;
    size_type offset{};
};

template<typename Container>
[[nodiscard]] inline constexpr bool operator==(const edge_iterator<Container> &lhs, const edge_iterator<Container> &rhs) noexcept {
    return lhs.pos == rhs.pos;
}

template<typename Container>
[[nodiscard]] inline constexpr bool operator!=(const edge_iterator<Container> &lhs, const edge_iterator<Container> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic implementation of a directed adjacency matrix.
 * @tparam Category Either a directed or undirected category tag.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Category, typename Allocator>
class adjacency_matrix {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_base_of_v<directed_tag, Category>, "Invalid graph category");
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::size_t>, "Invalid value type");
    using container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Vertex type. */
    using vertex_type = size_type;
    /*! @brief Edge type. */
    using edge_type = std::pair<vertex_type, vertex_type>;
    /*! @brief Vertex iterator type. */
    using vertex_iterator = iota_iterator<vertex_type>;
    /*! @brief Edge iterator type. */
    using edge_iterator = internal::edge_iterator<typename container_type::const_iterator>;
    /*! @brief Out edge iterator type. */
    using out_edge_iterator = edge_iterator;
    /*! @brief In edge iterator type. */
    using in_edge_iterator = edge_iterator;
    /*! @brief Graph category tag. */
    using graph_category = Category;

    /*! @brief Default constructor. */
    adjacency_matrix() noexcept(noexcept(allocator_type{}))
        : adjacency_matrix{0u} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit adjacency_matrix(const allocator_type &allocator) noexcept
        : adjacency_matrix{0u, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied number of vertices.
     * @param vertices Number of vertices.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(const size_type vertices, const allocator_type &allocator = allocator_type{})
        : matrix{vertices * vertices, allocator},
          vert{vertices} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    adjacency_matrix(const adjacency_matrix &other)
        : adjacency_matrix{other, other.get_allocator()} {}

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(const adjacency_matrix &other, const allocator_type &allocator)
        : matrix{other.matrix, allocator},
          vert{other.vert} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    adjacency_matrix(adjacency_matrix &&other) noexcept
        : adjacency_matrix{std::move(other), other.get_allocator()} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(adjacency_matrix &&other, const allocator_type &allocator)
        : matrix{std::move(other.matrix), allocator},
          vert{std::exchange(other.vert, 0u)} {}

    /**
     * @brief Default copy assignment operator.
     * @param other The instance to copy from.
     * @return This container.
     */
    adjacency_matrix &operator=(const adjacency_matrix &other) {
        matrix = other.matrix;
        vert = other.vert;
        return *this;
    }

    /**
     * @brief Default move assignment operator.
     * @param other The instance to move from.
     * @return This container.
     */
    adjacency_matrix &operator=(adjacency_matrix &&other) noexcept {
        matrix = std::move(other.matrix);
        vert = std::exchange(other.vert, 0u);
        return *this;
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return matrix.get_allocator();
    }

    /*! @brief Clears the adjacency matrix. */
    void clear() noexcept {
        matrix.clear();
        vert = {};
    }

    /**
     * @brief Exchanges the contents with those of a given adjacency matrix.
     * @param other Adjacency matrix to exchange the content with.
     */
    void swap(adjacency_matrix &other) {
        using std::swap;
        swap(matrix, other.matrix);
        swap(vert, other.vert);
    }

    /**
     * @brief Returns the number of vertices.
     * @return The number of vertices.
     */
    [[nodiscard]] size_type size() const noexcept {
        return vert;
    }

    /**
     * @brief Returns an iterable object to visit all vertices of a matrix.
     * @return An iterable object to visit all vertices of a matrix.
     */
    [[nodiscard]] iterable_adaptor<vertex_iterator> vertices() const noexcept {
        return {0u, vert};
    }

    /**
     * @brief Returns an iterable object to visit all edges of a matrix.
     * @return An iterable object to visit all edges of a matrix.
     */
    [[nodiscard]] iterable_adaptor<edge_iterator> edges() const noexcept {
        const auto it = matrix.cbegin();
        const auto sz = matrix.size();
        return {{it, vert, 0u, sz, 1u}, {it, vert, sz, sz, 1u}};
    }

    /**
     * @brief Returns an iterable object to visit all out edges of a vertex.
     * @param vertex The vertex of which to return all out edges.
     * @return An iterable object to visit all out edges of a vertex.
     */
    [[nodiscard]] iterable_adaptor<out_edge_iterator> out_edges(const vertex_type vertex) const noexcept {
        const auto it = matrix.cbegin();
        const auto from = vertex * vert;
        const auto to = vertex * vert + vert;
        return {{it, vert, from, to, 1u}, {it, vert, to, to, 1u}};
    }

    /**
     * @brief Returns an iterable object to visit all in edges of a vertex.
     * @param vertex The vertex of which to return all in edges.
     * @return An iterable object to visit all in edges of a vertex.
     */
    [[nodiscard]] iterable_adaptor<in_edge_iterator> in_edges(const vertex_type vertex) const noexcept {
        const auto it = matrix.cbegin();
        const auto from = vertex;
        const auto to = vert * (vert - 1u) + vertex;
        return {{it, vert, from, to, vert}, {it, vert, to, to, vert}};
    }

    /**
     * @brief Resizes an adjacency matrix.
     * @param vertices The new number of vertices.
     */
    void resize(const size_type vertices) {
        adjacency_matrix other{vertices, get_allocator()};

        for(auto [lhs, rhs]: edges()) {
            other.insert(lhs, rhs);
        }

        other.swap(*this);
    }

    /**
     * @brief Inserts an edge into the adjacency matrix, if it does not exist.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<edge_iterator, bool> insert(const vertex_type lhs, const vertex_type rhs) {
        const auto pos = lhs * vert + rhs;

        if constexpr(std::is_same_v<graph_category, undirected_tag>) {
            const auto rev = rhs * vert + lhs;
            ENTT_ASSERT(matrix[pos] == matrix[rev], "Something went really wrong");
            matrix[rev] = 1u;
        }

        const auto inserted = !std::exchange(matrix[pos], 1u);
        return {edge_iterator{matrix.cbegin(), vert, pos, matrix.size(), 1u}, inserted};
    }

    /**
     * @brief Removes the edge associated with a pair of given vertices.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const vertex_type lhs, const vertex_type rhs) {
        const auto pos = lhs * vert + rhs;

        if constexpr(std::is_same_v<graph_category, undirected_tag>) {
            const auto rev = rhs * vert + lhs;
            ENTT_ASSERT(matrix[pos] == matrix[rev], "Something went really wrong");
            matrix[rev] = 0u;
        }

        return std::exchange(matrix[pos], 0u);
    }

    /**
     * @brief Checks if an adjacency matrix contains a given edge.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return True if there is such an edge, false otherwise.
     */
    [[nodiscard]] bool contains(const vertex_type lhs, const vertex_type rhs) const {
        const auto pos = lhs * vert + rhs;
        return pos < matrix.size() && matrix[pos];
    }

private:
    container_type matrix;
    size_type vert;
};

} // namespace entt

#endif

// #include "graph/dot.hpp"
#ifndef ENTT_GRAPH_DOT_HPP
#define ENTT_GRAPH_DOT_HPP

#include <ostream>
#include <type_traits>
// #include "fwd.hpp"


namespace entt {

/**
 * @brief Outputs a graph in dot format.
 * @tparam Graph Graph type, valid as long as it exposes edges and vertices.
 * @tparam Writer Vertex decorator type.
 * @param out A standard output stream.
 * @param graph The graph to output.
 * @param writer Vertex decorator object.
 */
template<typename Graph, typename Writer>
void dot(std::ostream &out, const Graph &graph, Writer writer) {
    static_assert(std::is_base_of_v<directed_tag, typename Graph::graph_category>, "Invalid graph category");

    if constexpr(std::is_same_v<typename Graph::graph_category, undirected_tag>) {
        out << "graph{";
    } else {
        out << "digraph{";
    }

    for(auto &&vertex: graph.vertices()) {
        out << vertex << "[";
        writer(out, vertex);
        out << "];";
    }

    for(auto [lhs, rhs]: graph.edges()) {
        if constexpr(std::is_same_v<typename Graph::graph_category, undirected_tag>) {
            out << lhs << "--" << rhs << ";";
        } else {
            out << lhs << "->" << rhs << ";";
        }
    }

    out << "}";
}

/**
 * @brief Outputs a graph in dot format.
 * @tparam Graph Graph type, valid as long as it exposes edges and vertices.
 * @param out A standard output stream.
 * @param graph The graph to output.
 */
template<typename Graph>
void dot(std::ostream &out, const Graph &graph) {
    return dot(out, graph, [](auto &&...) {});
}

} // namespace entt

#endif

// #include "graph/flow.hpp"
#ifndef ENTT_GRAPH_FLOW_HPP
#define ENTT_GRAPH_FLOW_HPP

#include <algorithm>
#include <cstddef>
#include <functional>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../container/dense_map.hpp"
#ifndef ENTT_CONTAINER_DENSE_MAP_HPP
#define ENTT_CONTAINER_DENSE_MAP_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CONTAINER_FWD_HPP
#define ENTT_CONTAINER_FWD_HPP

#include <functional>
#include <memory>

namespace entt {

template<
    typename Key,
    typename Type,
    typename = std::hash<Key>,
    typename = std::equal_to<Key>,
    typename = std::allocator<std::pair<const Key, Type>>>
class dense_map;

template<
    typename Type,
    typename = std::hash<Type>,
    typename = std::equal_to<Type>,
    typename = std::allocator<Type>>
class dense_set;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Key, typename Type>
struct dense_map_node final {
    using value_type = std::pair<Key, Type>;

    template<typename... Args>
    dense_map_node(const std::size_t pos, Args &&...args)
        : next{pos},
          element{std::forward<Args>(args)...} {}

    template<typename Allocator, typename... Args>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const std::size_t pos, Args &&...args)
        : next{pos},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::forward<Args>(args)...)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const dense_map_node &other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, other.element)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, dense_map_node &&other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::move(other.element))} {}

    std::size_t next;
    value_type element;
};

template<typename It>
class dense_map_iterator final {
    template<typename>
    friend class dense_map_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_iterator() noexcept
        : it{} {}

    constexpr dense_map_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_iterator(const dense_map_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_map_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_map_iterator operator++(int) noexcept {
        dense_map_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_map_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_map_iterator operator--(int) noexcept {
        dense_map_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_map_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_map_iterator operator+(const difference_type value) const noexcept {
        dense_map_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_map_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_map_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].element.first, it[value].element.second};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->element.first, it->element.second};
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_map_local_iterator final {
    template<typename>
    friend class dense_map_local_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_map_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_local_iterator(const dense_map_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_map_local_iterator &operator++() noexcept {
        return offset = it[offset].next, *this;
    }

    constexpr dense_map_local_iterator operator++(int) noexcept {
        dense_map_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it[offset].element.first, it[offset].element.second};
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for key-value pairs with unique keys.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on the hash of its key. Keys with the same hash
 * code appear in the same bucket.
 *
 * @tparam Key Key type of the associative container.
 * @tparam Type Mapped type of the associative container.
 * @tparam Hash Type of function to use to hash the keys.
 * @tparam KeyEqual Type of function to use to compare the keys for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Key, typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_map {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = internal::dense_map_node<Key, Type>;
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::pair<const Key, Type>>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t key_to_bucket(const Other &key) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(key)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other, typename... Args>
    [[nodiscard]] auto insert_or_do_nothing(Other &&key, Args &&...args) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::piecewise_construct, std::forward_as_tuple(std::forward<Other>(key)), std::forward_as_tuple(std::forward<Args>(args)...));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    template<typename Other, typename Arg>
    [[nodiscard]] auto insert_or_overwrite(Other &&key, Arg &&value) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            it->second = std::forward<Arg>(value);
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(key), std::forward<Arg>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + key_to_bucket(packed.first().back().element.first);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].next) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Key;
    /*! @brief Mapped type of the container. */
    using mapped_type = Type;
    /*! @brief Key-value type of the container. */
    using value_type = std::pair<const Key, Type>;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the keys. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the keys for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Input iterator type. */
    using iterator = internal::dense_map_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_iterator = internal::dense_map_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Input iterator type. */
    using local_iterator = internal::dense_map_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_local_iterator = internal::dense_map_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_map()
        : dense_map{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const allocator_type &allocator)
        : dense_map{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const allocator_type &allocator)
        : dense_map{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_map{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_map(const dense_map &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_map(const dense_map &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_map(dense_map &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_map(dense_map &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_map &operator=(const dense_map &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_map &operator=(dense_map &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if the key does not exist.
     * @param value A key-value pair eventually convertible to the value type.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value.first, value.second);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value.first), std::move(value.second));
    }

    /**
     * @copydoc insert
     * @tparam Arg Type of the key-value pair to insert into the container.
     */
    template<typename Arg>
    std::enable_if_t<std::is_constructible_v<value_type, Arg &&>, std::pair<iterator, bool>>
    insert(Arg &&value) {
        return insert_or_do_nothing(std::forward<Arg>(value).first, std::forward<Arg>(value).second);
    }

    /**
     * @brief Inserts elements into the container, if their keys do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Inserts an element into the container or assigns to the current
     * element if the key already exists.
     * @tparam Arg Type of the value to insert or assign.
     * @param key A key used both to look up and to insert if not found.
     * @param value A value to insert or assign.
     * @return A pair consisting of an iterator to the element and a bool
     * denoting whether the insertion took place.
     */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(const key_type &key, Arg &&value) {
        return insert_or_overwrite(key, std::forward<Arg>(value));
    }

    /*! @copydoc insert_or_assign */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(key_type &&key, Arg &&value) {
        return insert_or_overwrite(std::move(key), std::forward<Arg>(value));
    }

    /**
     * @brief Constructs an element in-place, if the key does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace([[maybe_unused]] Args &&...args) {
        if constexpr(sizeof...(Args) == 0u) {
            return insert_or_do_nothing(key_type{});
        } else if constexpr(sizeof...(Args) == 1u) {
            return insert_or_do_nothing(std::forward<Args>(args).first..., std::forward<Args>(args).second...);
        } else if constexpr(sizeof...(Args) == 2u) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(packed.first().size(), std::forward<Args>(args)...);
            const auto index = key_to_bucket(node.element.first);

            if(auto it = constrained_find(node.element.first, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.next, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Inserts in-place if the key does not exist, does nothing if the
     * key exists.
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param key A key used both to look up and to insert if not found.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(const key_type &key, Args &&...args) {
        return insert_or_do_nothing(key, std::forward<Args>(args)...);
    }

    /*! @copydoc try_emplace */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(key_type &&key, Args &&...args) {
        return insert_or_do_nothing(std::move(key), std::forward<Args>(args)...);
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(pos->first);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].element.first);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given key.
     * @param key A key value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const key_type &key) {
        for(size_type *curr = sparse.first().data() + key_to_bucket(key); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].next) {
            if(packed.second()(packed.first()[*curr].element.first, key)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].next;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_map &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Accesses a given element with bounds checking.
     * @param key A key of an element to find.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &at(const key_type &key) {
        auto it = find(key);
        ENTT_ASSERT(it != end(), "Invalid key");
        return it->second;
    }

    /*! @copydoc at */
    [[nodiscard]] const mapped_type &at(const key_type &key) const {
        auto it = find(key);
        ENTT_ASSERT(it != cend(), "Invalid key");
        return it->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](const key_type &key) {
        return insert_or_do_nothing(key).first->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](key_type &&key) {
        return insert_or_do_nothing(std::move(key)).first->second;
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const key_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given key.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const key_type &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const key_type &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Finds an element with a key that compares _equivalent_ to a given
     * key.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Returns a range containing all elements with a given key.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const key_type &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const key_type &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given key.
     * @tparam Other Type of an element to search for.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given key.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const key_type &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Checks if the container contains an element with a key that
     * compares _equivalent_ to a given value.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given key.
     * @param key The value of the key to examine.
     * @return The bucket for the given key.
     */
    [[nodiscard]] size_type bucket(const key_type &key) const {
        return key_to_bucket(key);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = key_to_bucket(packed.first()[pos].element.first);
                packed.first()[pos].next = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the keys.
     * @return The function used to hash the keys.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare keys for equality.
     * @return The function used to compare keys for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace std {

template<typename Key, typename Value, typename Allocator>
struct uses_allocator<entt::internal::dense_map_node<Key, Value>, Allocator>
    : std::true_type {};

} // namespace std

/**
 * Internal details not to be documented.
 * @endcond
 */

#endif

// #include "../container/dense_set.hpp"
#ifndef ENTT_CONTAINER_DENSE_SET_HPP
#define ENTT_CONTAINER_DENSE_SET_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/compressed_pair.hpp"

// #include "../core/memory.hpp"

// #include "../core/type_traits.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class dense_set_iterator final {
    template<typename>
    friend class dense_set_iterator;

public:
    using value_type = typename It::value_type::second_type;
    using pointer = const value_type *;
    using reference = const value_type &;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::random_access_iterator_tag;

    constexpr dense_set_iterator() noexcept
        : it{} {}

    constexpr dense_set_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_set_iterator(const dense_set_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_set_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_set_iterator operator++(int) noexcept {
        dense_set_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_set_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_set_iterator operator--(int) noexcept {
        dense_set_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_set_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_set_iterator operator+(const difference_type value) const noexcept {
        dense_set_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_set_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_set_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return it[value].second;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::addressof(it->second);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_set_local_iterator final {
    template<typename>
    friend class dense_set_local_iterator;

public:
    using value_type = typename It::value_type::second_type;
    using pointer = const value_type *;
    using reference = const value_type &;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::forward_iterator_tag;

    constexpr dense_set_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_set_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_set_local_iterator(const dense_set_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_set_local_iterator &operator++() noexcept {
        return offset = it[offset].first, *this;
    }

    constexpr dense_set_local_iterator operator++(int) noexcept {
        dense_set_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::addressof(it[offset].second);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_set_local_iterator<ILhs> &lhs, const dense_set_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_set_local_iterator<ILhs> &lhs, const dense_set_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for unique objects of a given type.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on its hash. Elements with the same hash code
 * appear in the same bucket.
 *
 * @tparam Type Value type of the associative container.
 * @tparam Hash Type of function to use to hash the values.
 * @tparam KeyEqual Type of function to use to compare the values for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_set {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = std::pair<std::size_t, Type>;
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t value_to_bucket(const Other &value) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(value)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &value, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(*it, value)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &value, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(*it, value)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other>
    [[nodiscard]] auto insert_or_do_nothing(Other &&value) {
        const auto index = value_to_bucket(value);

        if(auto it = constrained_find(value, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + value_to_bucket(packed.first().back().second);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].first) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Type;
    /*! @brief Value type of the container. */
    using value_type = Type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the elements. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the elements for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Random access iterator type. */
    using iterator = internal::dense_set_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant random access iterator type. */
    using const_iterator = internal::dense_set_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Forward iterator type. */
    using local_iterator = internal::dense_set_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant forward iterator type. */
    using const_local_iterator = internal::dense_set_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_set()
        : dense_set{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_set(const allocator_type &allocator)
        : dense_set{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_set(const size_type cnt, const allocator_type &allocator)
        : dense_set{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_set(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_set{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_set(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_set(const dense_set &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_set(const dense_set &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_set(dense_set &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_set(dense_set &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_set &operator=(const dense_set &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_set &operator=(dense_set &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if it does not exist.
     * @param value An element to insert into the container.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value));
    }

    /**
     * @brief Inserts elements into the container, if they do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Constructs an element in-place, if it does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace(Args &&...args) {
        if constexpr(((sizeof...(Args) == 1u) && ... && std::is_same_v<std::decay_t<Args>, value_type>)) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(std::piecewise_construct, std::make_tuple(packed.first().size()), std::forward_as_tuple(std::forward<Args>(args)...));
            const auto index = value_to_bucket(node.second);

            if(auto it = constrained_find(node.second, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.first, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(*pos);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].second);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given value.
     * @param value Value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const value_type &value) {
        for(size_type *curr = sparse.first().data() + value_to_bucket(value); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].first) {
            if(packed.second()(packed.first()[*curr].second, value)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].first;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_set &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Returns the number of elements matching a value (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const value_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given value.
     * @param value Value of an element to search for.
     * @return An iterator to an element with the given value. If no such
     * element is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const value_type &value) {
        return constrained_find(value, value_to_bucket(value));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const value_type &value) const {
        return constrained_find(value, value_to_bucket(value));
    }

    /**
     * @brief Finds an element that compares _equivalent_ to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return An iterator to an element with the given value. If no such
     * element is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &value) {
        return constrained_find(value, value_to_bucket(value));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &value) const {
        return constrained_find(value, value_to_bucket(value));
    }

    /**
     * @brief Returns a range containing all elements with a given value.
     * @param value Value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const value_type &value) {
        const auto it = find(value);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const value_type &value) const {
        const auto it = find(value);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &value) {
        const auto it = find(value);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &value) const {
        const auto it = find(value);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given value.
     * @param value Value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const value_type &value) const {
        return (find(value) != cend());
    }

    /**
     * @brief Checks if the container contains an element that compares
     * _equivalent_ to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &value) const {
        return (find(value) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given element.
     * @param value The value of the element to examine.
     * @return The bucket for the given element.
     */
    [[nodiscard]] size_type bucket(const value_type &value) const {
        return value_to_bucket(value);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = value_to_bucket(packed.first()[pos].second);
                packed.first()[pos].first = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the elements.
     * @return The function used to hash the elements.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare elements for equality.
     * @return The function used to compare elements for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/fwd.hpp"

// #include "../core/iterator.hpp"

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "adjacency_matrix.hpp"
#ifndef ENTT_GRAPH_ADJACENCY_MATRIX_HPP
#define ENTT_GRAPH_ADJACENCY_MATRIX_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/iterator.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class edge_iterator {
    using size_type = std::size_t;

public:
    using value_type = std::pair<size_type, size_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr edge_iterator() noexcept
        : it{},
          vert{},
          pos{},
          last{},
          offset{} {}

    constexpr edge_iterator(It base, const size_type vertices, const size_type from, const size_type to, const size_type step) noexcept
        : it{std::move(base)},
          vert{vertices},
          pos{from},
          last{to},
          offset{step} {
        for(; pos != last && !it[pos]; pos += offset) {}
    }

    constexpr edge_iterator &operator++() noexcept {
        for(pos += offset; pos != last && !it[pos]; pos += offset) {}
        return *this;
    }

    constexpr edge_iterator operator++(int) noexcept {
        edge_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::make_pair<size_type>(pos / vert, pos % vert);
    }

    template<typename Type>
    friend constexpr bool operator==(const edge_iterator<Type> &, const edge_iterator<Type> &) noexcept;

private:
    It it;
    size_type vert;
    size_type pos;
    size_type last;
    size_type offset{};
};

template<typename Container>
[[nodiscard]] inline constexpr bool operator==(const edge_iterator<Container> &lhs, const edge_iterator<Container> &rhs) noexcept {
    return lhs.pos == rhs.pos;
}

template<typename Container>
[[nodiscard]] inline constexpr bool operator!=(const edge_iterator<Container> &lhs, const edge_iterator<Container> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic implementation of a directed adjacency matrix.
 * @tparam Category Either a directed or undirected category tag.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Category, typename Allocator>
class adjacency_matrix {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_base_of_v<directed_tag, Category>, "Invalid graph category");
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::size_t>, "Invalid value type");
    using container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Vertex type. */
    using vertex_type = size_type;
    /*! @brief Edge type. */
    using edge_type = std::pair<vertex_type, vertex_type>;
    /*! @brief Vertex iterator type. */
    using vertex_iterator = iota_iterator<vertex_type>;
    /*! @brief Edge iterator type. */
    using edge_iterator = internal::edge_iterator<typename container_type::const_iterator>;
    /*! @brief Out edge iterator type. */
    using out_edge_iterator = edge_iterator;
    /*! @brief In edge iterator type. */
    using in_edge_iterator = edge_iterator;
    /*! @brief Graph category tag. */
    using graph_category = Category;

    /*! @brief Default constructor. */
    adjacency_matrix() noexcept(noexcept(allocator_type{}))
        : adjacency_matrix{0u} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit adjacency_matrix(const allocator_type &allocator) noexcept
        : adjacency_matrix{0u, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied number of vertices.
     * @param vertices Number of vertices.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(const size_type vertices, const allocator_type &allocator = allocator_type{})
        : matrix{vertices * vertices, allocator},
          vert{vertices} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    adjacency_matrix(const adjacency_matrix &other)
        : adjacency_matrix{other, other.get_allocator()} {}

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(const adjacency_matrix &other, const allocator_type &allocator)
        : matrix{other.matrix, allocator},
          vert{other.vert} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    adjacency_matrix(adjacency_matrix &&other) noexcept
        : adjacency_matrix{std::move(other), other.get_allocator()} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    adjacency_matrix(adjacency_matrix &&other, const allocator_type &allocator)
        : matrix{std::move(other.matrix), allocator},
          vert{std::exchange(other.vert, 0u)} {}

    /**
     * @brief Default copy assignment operator.
     * @param other The instance to copy from.
     * @return This container.
     */
    adjacency_matrix &operator=(const adjacency_matrix &other) {
        matrix = other.matrix;
        vert = other.vert;
        return *this;
    }

    /**
     * @brief Default move assignment operator.
     * @param other The instance to move from.
     * @return This container.
     */
    adjacency_matrix &operator=(adjacency_matrix &&other) noexcept {
        matrix = std::move(other.matrix);
        vert = std::exchange(other.vert, 0u);
        return *this;
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return matrix.get_allocator();
    }

    /*! @brief Clears the adjacency matrix. */
    void clear() noexcept {
        matrix.clear();
        vert = {};
    }

    /**
     * @brief Exchanges the contents with those of a given adjacency matrix.
     * @param other Adjacency matrix to exchange the content with.
     */
    void swap(adjacency_matrix &other) {
        using std::swap;
        swap(matrix, other.matrix);
        swap(vert, other.vert);
    }

    /**
     * @brief Returns the number of vertices.
     * @return The number of vertices.
     */
    [[nodiscard]] size_type size() const noexcept {
        return vert;
    }

    /**
     * @brief Returns an iterable object to visit all vertices of a matrix.
     * @return An iterable object to visit all vertices of a matrix.
     */
    [[nodiscard]] iterable_adaptor<vertex_iterator> vertices() const noexcept {
        return {0u, vert};
    }

    /**
     * @brief Returns an iterable object to visit all edges of a matrix.
     * @return An iterable object to visit all edges of a matrix.
     */
    [[nodiscard]] iterable_adaptor<edge_iterator> edges() const noexcept {
        const auto it = matrix.cbegin();
        const auto sz = matrix.size();
        return {{it, vert, 0u, sz, 1u}, {it, vert, sz, sz, 1u}};
    }

    /**
     * @brief Returns an iterable object to visit all out edges of a vertex.
     * @param vertex The vertex of which to return all out edges.
     * @return An iterable object to visit all out edges of a vertex.
     */
    [[nodiscard]] iterable_adaptor<out_edge_iterator> out_edges(const vertex_type vertex) const noexcept {
        const auto it = matrix.cbegin();
        const auto from = vertex * vert;
        const auto to = vertex * vert + vert;
        return {{it, vert, from, to, 1u}, {it, vert, to, to, 1u}};
    }

    /**
     * @brief Returns an iterable object to visit all in edges of a vertex.
     * @param vertex The vertex of which to return all in edges.
     * @return An iterable object to visit all in edges of a vertex.
     */
    [[nodiscard]] iterable_adaptor<in_edge_iterator> in_edges(const vertex_type vertex) const noexcept {
        const auto it = matrix.cbegin();
        const auto from = vertex;
        const auto to = vert * (vert - 1u) + vertex;
        return {{it, vert, from, to, vert}, {it, vert, to, to, vert}};
    }

    /**
     * @brief Resizes an adjacency matrix.
     * @param vertices The new number of vertices.
     */
    void resize(const size_type vertices) {
        adjacency_matrix other{vertices, get_allocator()};

        for(auto [lhs, rhs]: edges()) {
            other.insert(lhs, rhs);
        }

        other.swap(*this);
    }

    /**
     * @brief Inserts an edge into the adjacency matrix, if it does not exist.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<edge_iterator, bool> insert(const vertex_type lhs, const vertex_type rhs) {
        const auto pos = lhs * vert + rhs;

        if constexpr(std::is_same_v<graph_category, undirected_tag>) {
            const auto rev = rhs * vert + lhs;
            ENTT_ASSERT(matrix[pos] == matrix[rev], "Something went really wrong");
            matrix[rev] = 1u;
        }

        const auto inserted = !std::exchange(matrix[pos], 1u);
        return {edge_iterator{matrix.cbegin(), vert, pos, matrix.size(), 1u}, inserted};
    }

    /**
     * @brief Removes the edge associated with a pair of given vertices.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const vertex_type lhs, const vertex_type rhs) {
        const auto pos = lhs * vert + rhs;

        if constexpr(std::is_same_v<graph_category, undirected_tag>) {
            const auto rev = rhs * vert + lhs;
            ENTT_ASSERT(matrix[pos] == matrix[rev], "Something went really wrong");
            matrix[rev] = 0u;
        }

        return std::exchange(matrix[pos], 0u);
    }

    /**
     * @brief Checks if an adjacency matrix contains a given edge.
     * @param lhs The left hand vertex of the edge.
     * @param rhs The right hand vertex of the edge.
     * @return True if there is such an edge, false otherwise.
     */
    [[nodiscard]] bool contains(const vertex_type lhs, const vertex_type rhs) const {
        const auto pos = lhs * vert + rhs;
        return pos < matrix.size() && matrix[pos];
    }

private:
    container_type matrix;
    size_type vert;
};

} // namespace entt

#endif

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class for creating task graphs.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Allocator>
class basic_flow {
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, id_type>, "Invalid value type");
    using task_container_type = dense_set<id_type, identity, std::equal_to<id_type>, typename alloc_traits::template rebind_alloc<id_type>>;
    using ro_rw_container_type = std::vector<std::pair<std::size_t, bool>, typename alloc_traits::template rebind_alloc<std::pair<std::size_t, bool>>>;
    using deps_container_type = dense_map<id_type, ro_rw_container_type, identity, std::equal_to<id_type>, typename alloc_traits::template rebind_alloc<std::pair<const id_type, ro_rw_container_type>>>;

    void emplace(const id_type res, const bool is_rw) {
        ENTT_ASSERT(index.first() < vertices.size(), "Invalid node");

        if(!deps.contains(res) && sync_on != vertices.size()) {
            deps[res].emplace_back(sync_on, true);
        }

        deps[res].emplace_back(index.first(), is_rw);
    }

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Iterable task list. */
    using iterable = iterable_adaptor<typename task_container_type::const_iterator>;

    /*! @brief Default constructor. */
    basic_flow()
        : basic_flow{allocator_type{}} {}

    /**
     * @brief Constructs a flow builder with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_flow(const allocator_type &allocator)
        : index{0u, allocator},
          vertices{},
          deps{},
          sync_on{} {}

    /*! @brief Default copy constructor. */
    basic_flow(const basic_flow &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    basic_flow(const basic_flow &other, const allocator_type &allocator)
        : index{other.index.first(), allocator},
          vertices{other.vertices, allocator},
          deps{other.deps, allocator},
          sync_on{other.sync_on} {}

    /*! @brief Default move constructor. */
    basic_flow(basic_flow &&) noexcept = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_flow(basic_flow &&other, const allocator_type &allocator)
        : index{other.index.first(), allocator},
          vertices{std::move(other.vertices), allocator},
          deps{std::move(other.deps), allocator},
          sync_on{other.sync_on} {}

    /**
     * @brief Default copy assignment operator.
     * @return This flow builder.
     */
    basic_flow &operator=(const basic_flow &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This flow builder.
     */
    basic_flow &operator=(basic_flow &&) noexcept = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return allocator_type{index.second()};
    }

    /**
     * @brief Returns the identifier at specified location.
     * @param pos Position of the identifier to return.
     * @return The requested identifier.
     */
    [[nodiscard]] id_type operator[](const size_type pos) const {
        return vertices.cbegin()[pos];
    }

    /*! @brief Clears the flow builder. */
    void clear() noexcept {
        index.first() = sync_on = {};
        vertices.clear();
        deps.clear();
    }

    /**
     * @brief Exchanges the contents with those of a given flow builder.
     * @param other Flow builder to exchange the content with.
     */
    void swap(basic_flow &other) {
        using std::swap;
        std::swap(index, other.index);
        std::swap(vertices, other.vertices);
        std::swap(deps, other.deps);
        std::swap(sync_on, other.sync_on);
    }

    /**
     * @brief Returns the number of tasks.
     * @return The number of tasks.
     */
    [[nodiscard]] size_type size() const noexcept {
        return vertices.size();
    }

    /**
     * @brief Binds a task to a flow builder.
     * @param value Task identifier.
     * @return This flow builder.
     */
    basic_flow &bind(const id_type value) {
        sync_on += (sync_on == vertices.size());
        const auto it = vertices.emplace(value).first;
        index.first() = size_type(it - vertices.begin());
        return *this;
    }

    /**
     * @brief Turns the current task into a sync point.
     * @return This flow builder.
     */
    basic_flow &sync() {
        ENTT_ASSERT(index.first() < vertices.size(), "Invalid node");
        sync_on = index.first();

        for(const auto &elem: deps) {
            elem.second.emplace_back(sync_on, true);
        }

        return *this;
    }

    /**
     * @brief Assigns a resource to the current task with a given access mode.
     * @param res Resource identifier.
     * @param is_rw Access mode.
     * @return This flow builder.
     */
    basic_flow &set(const id_type res, bool is_rw = false) {
        emplace(res, is_rw);
        return *this;
    }

    /**
     * @brief Assigns a read-only resource to the current task.
     * @param res Resource identifier.
     * @return This flow builder.
     */
    basic_flow &ro(const id_type res) {
        emplace(res, false);
        return *this;
    }

    /**
     * @brief Assigns a range of read-only resources to the current task.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return This flow builder.
     */
    template<typename It>
    std::enable_if_t<std::is_same_v<std::remove_const_t<typename std::iterator_traits<It>::value_type>, id_type>, basic_flow &>
    ro(It first, It last) {
        for(; first != last; ++first) {
            emplace(*first, false);
        }

        return *this;
    }

    /**
     * @brief Assigns a writable resource to the current task.
     * @param res Resource identifier.
     * @return This flow builder.
     */
    basic_flow &rw(const id_type res) {
        emplace(res, true);
        return *this;
    }

    /**
     * @brief Assigns a range of writable resources to the current task.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return This flow builder.
     */
    template<typename It>
    std::enable_if_t<std::is_same_v<std::remove_const_t<typename std::iterator_traits<It>::value_type>, id_type>, basic_flow &>
    rw(It first, It last) {
        for(; first != last; ++first) {
            emplace(*first, true);
        }

        return *this;
    }

    /**
     * @brief Generates a task graph for the current content.
     * @return The adjacency matrix of the task graph.
     */
    [[nodiscard]] adjacency_matrix<directed_tag> graph() const {
        const auto length = vertices.size();
        adjacency_matrix<directed_tag> matrix{length};

        // creates the adjacency matrix
        for(const auto &elem: deps) {
            const auto last = elem.second.cend();
            auto it = elem.second.cbegin();

            while(it != last) {
                if(it->second) {
                    // rw item
                    if(auto curr = it++; it != last) {
                        if(it->second) {
                            matrix.insert(curr->first, it->first);
                        } else if(const auto next = std::find_if(it, last, [](const auto &value) { return value.second; }); next != last) {
                            for(; it != next; ++it) {
                                matrix.insert(curr->first, it->first);
                                matrix.insert(it->first, next->first);
                            }
                        } else {
                            for(; it != next; ++it) {
                                matrix.insert(curr->first, it->first);
                            }
                        }
                    }
                } else {
                    // ro item (first iteration only)
                    if(const auto next = std::find_if(it, last, [](const auto &value) { return value.second; }); next != last) {
                        for(; it != next; ++it) {
                            matrix.insert(it->first, next->first);
                        }
                    } else {
                        it = last;
                    }
                }
            }
        }

        // computes the transitive closure
        for(std::size_t vk{}; vk < length; ++vk) {
            for(std::size_t vi{}; vi < length; ++vi) {
                for(std::size_t vj{}; vj < length; ++vj) {
                    if(matrix.contains(vi, vk) && matrix.contains(vk, vj)) {
                        matrix.insert(vi, vj);
                    }
                }
            }
        }

        // applies the transitive reduction
        for(std::size_t vert{}; vert < length; ++vert) {
            matrix.erase(vert, vert);
        }

        for(std::size_t vj{}; vj < length; ++vj) {
            for(std::size_t vi{}; vi < length; ++vi) {
                if(matrix.contains(vi, vj)) {
                    for(std::size_t vk{}; vk < length; ++vk) {
                        if(matrix.contains(vj, vk)) {
                            matrix.erase(vi, vk);
                        }
                    }
                }
            }
        }

        return matrix;
    }

private:
    compressed_pair<size_type, allocator_type> index;
    task_container_type vertices;
    deps_container_type deps;
    size_type sync_on;
};

} // namespace entt

#endif

// #include "locator/locator.hpp"
#ifndef ENTT_LOCATOR_LOCATOR_HPP
#define ENTT_LOCATOR_LOCATOR_HPP

#include <memory>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif


namespace entt {

/**
 * @brief Service locator, nothing more.
 *
 * A service locator is used to do what it promises: locate services.<br/>
 * Usually service locators are tightly bound to the services they expose and
 * thus it's hard to define a general purpose class to do that. This tiny class
 * tries to fill the gap and to get rid of the burden of defining a different
 * specific locator for each application.
 *
 * @note
 * Users shouldn't retain references to a service. The recommended way is to
 * retrieve the service implementation currently set each and every time the
 * need for it arises. The risk is to incur in unexpected behaviors otherwise.
 *
 * @tparam Service Service type.
 */
template<typename Service>
class locator final {
    class service_handle {
        friend class locator<Service>;
        std::shared_ptr<Service> value{};
    };

public:
    /*! @brief Service type. */
    using type = Service;
    /*! @brief Service node type. */
    using node_type = service_handle;

    /*! @brief Default constructor, deleted on purpose. */
    locator() = delete;
    /*! @brief Default destructor, deleted on purpose. */
    ~locator() = delete;

    /**
     * @brief Checks whether a service locator contains a value.
     * @return True if the service locator contains a value, false otherwise.
     */
    [[nodiscard]] static bool has_value() noexcept {
        return (service != nullptr);
    }

    /**
     * @brief Returns a reference to a valid service, if any.
     *
     * @warning
     * Invoking this function can result in undefined behavior if the service
     * hasn't been set yet.
     *
     * @return A reference to the service currently set, if any.
     */
    [[nodiscard]] static Service &value() noexcept {
        ENTT_ASSERT(has_value(), "Service not available");
        return *service;
    }

    /**
     * @brief Returns a service if available or sets it from a fallback type.
     *
     * Arguments are used only if a service doesn't already exist. In all other
     * cases, they are discarded.
     *
     * @tparam Args Types of arguments to use to construct the fallback service.
     * @tparam Impl Fallback service type.
     * @param args Parameters to use to construct the fallback service.
     * @return A reference to a valid service.
     */
    template<typename Impl = Service, typename... Args>
    [[nodiscard]] static Service &value_or(Args &&...args) {
        return service ? *service : emplace<Impl>(std::forward<Args>(args)...);
    }

    /**
     * @brief Sets or replaces a service.
     * @tparam Impl Service type.
     * @tparam Args Types of arguments to use to construct the service.
     * @param args Parameters to use to construct the service.
     * @return A reference to a valid service.
     */
    template<typename Impl = Service, typename... Args>
    static Service &emplace(Args &&...args) {
        service = std::make_shared<Impl>(std::forward<Args>(args)...);
        return *service;
    }

    /**
     * @brief Sets or replaces a service using a given allocator.
     * @tparam Impl Service type.
     * @tparam Allocator Type of allocator used to manage memory and elements.
     * @tparam Args Types of arguments to use to construct the service.
     * @param alloc The allocator to use.
     * @param args Parameters to use to construct the service.
     * @return A reference to a valid service.
     */
    template<typename Impl = Service, typename Allocator, typename... Args>
    static Service &allocate_emplace(Allocator alloc, Args &&...args) {
        service = std::allocate_shared<Impl>(alloc, std::forward<Args>(args)...);
        return *service;
    }

    /**
     * @brief Returns a handle to the underlying service.
     * @return A handle to the underlying service.
     */
    static node_type handle() noexcept {
        node_type node{};
        node.value = service;
        return node;
    }

    /**
     * @brief Resets or replaces a service.
     * @param other Optional handle with which to replace the service.
     */
    static void reset(const node_type &other = {}) noexcept {
        service = other.value;
    }

private:
    // std::shared_ptr because of its type erased allocator which is useful here
    inline static std::shared_ptr<Service> service{};
};

} // namespace entt

#endif

// #include "meta/adl_pointer.hpp"
#ifndef ENTT_META_ADL_POINTER_HPP
#define ENTT_META_ADL_POINTER_HPP

namespace entt {

/**
 * @brief ADL based lookup function for dereferencing meta pointer-like types.
 * @tparam Type Element type.
 * @param value A pointer-like object.
 * @return The value returned from the dereferenced pointer.
 */
template<typename Type>
decltype(auto) dereference_meta_pointer_like(const Type &value) {
    return *value;
}

/**
 * @brief Fake ADL based lookup function for meta pointer-like types.
 * @tparam Type Element type.
 */
template<typename Type>
struct adl_meta_pointer_like {
    /**
     * @brief Uses the default ADL based lookup method to resolve the call.
     * @param value A pointer-like object.
     * @return The value returned from the dereferenced pointer.
     */
    static decltype(auto) dereference(const Type &value) {
        return dereference_meta_pointer_like(value);
    }
};

} // namespace entt

#endif

// #include "meta/container.hpp"
#ifndef ENTT_META_CONTAINER_HPP
#define ENTT_META_CONTAINER_HPP

#include <array>
#include <deque>
#include <iterator>
#include <list>
#include <map>
#include <set>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <vector>
// #include "../container/dense_map.hpp"
#ifndef ENTT_CONTAINER_DENSE_MAP_HPP
#define ENTT_CONTAINER_DENSE_MAP_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CONTAINER_FWD_HPP
#define ENTT_CONTAINER_FWD_HPP

#include <functional>
#include <memory>

namespace entt {

template<
    typename Key,
    typename Type,
    typename = std::hash<Key>,
    typename = std::equal_to<Key>,
    typename = std::allocator<std::pair<const Key, Type>>>
class dense_map;

template<
    typename Type,
    typename = std::hash<Type>,
    typename = std::equal_to<Type>,
    typename = std::allocator<Type>>
class dense_set;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Key, typename Type>
struct dense_map_node final {
    using value_type = std::pair<Key, Type>;

    template<typename... Args>
    dense_map_node(const std::size_t pos, Args &&...args)
        : next{pos},
          element{std::forward<Args>(args)...} {}

    template<typename Allocator, typename... Args>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const std::size_t pos, Args &&...args)
        : next{pos},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::forward<Args>(args)...)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const dense_map_node &other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, other.element)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, dense_map_node &&other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::move(other.element))} {}

    std::size_t next;
    value_type element;
};

template<typename It>
class dense_map_iterator final {
    template<typename>
    friend class dense_map_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_iterator() noexcept
        : it{} {}

    constexpr dense_map_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_iterator(const dense_map_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_map_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_map_iterator operator++(int) noexcept {
        dense_map_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_map_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_map_iterator operator--(int) noexcept {
        dense_map_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_map_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_map_iterator operator+(const difference_type value) const noexcept {
        dense_map_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_map_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_map_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].element.first, it[value].element.second};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->element.first, it->element.second};
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_map_local_iterator final {
    template<typename>
    friend class dense_map_local_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_map_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_local_iterator(const dense_map_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_map_local_iterator &operator++() noexcept {
        return offset = it[offset].next, *this;
    }

    constexpr dense_map_local_iterator operator++(int) noexcept {
        dense_map_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it[offset].element.first, it[offset].element.second};
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for key-value pairs with unique keys.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on the hash of its key. Keys with the same hash
 * code appear in the same bucket.
 *
 * @tparam Key Key type of the associative container.
 * @tparam Type Mapped type of the associative container.
 * @tparam Hash Type of function to use to hash the keys.
 * @tparam KeyEqual Type of function to use to compare the keys for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Key, typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_map {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = internal::dense_map_node<Key, Type>;
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::pair<const Key, Type>>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t key_to_bucket(const Other &key) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(key)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other, typename... Args>
    [[nodiscard]] auto insert_or_do_nothing(Other &&key, Args &&...args) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::piecewise_construct, std::forward_as_tuple(std::forward<Other>(key)), std::forward_as_tuple(std::forward<Args>(args)...));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    template<typename Other, typename Arg>
    [[nodiscard]] auto insert_or_overwrite(Other &&key, Arg &&value) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            it->second = std::forward<Arg>(value);
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(key), std::forward<Arg>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + key_to_bucket(packed.first().back().element.first);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].next) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Key;
    /*! @brief Mapped type of the container. */
    using mapped_type = Type;
    /*! @brief Key-value type of the container. */
    using value_type = std::pair<const Key, Type>;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the keys. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the keys for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Input iterator type. */
    using iterator = internal::dense_map_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_iterator = internal::dense_map_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Input iterator type. */
    using local_iterator = internal::dense_map_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_local_iterator = internal::dense_map_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_map()
        : dense_map{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const allocator_type &allocator)
        : dense_map{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const allocator_type &allocator)
        : dense_map{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_map{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_map(const dense_map &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_map(const dense_map &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_map(dense_map &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_map(dense_map &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_map &operator=(const dense_map &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_map &operator=(dense_map &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if the key does not exist.
     * @param value A key-value pair eventually convertible to the value type.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value.first, value.second);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value.first), std::move(value.second));
    }

    /**
     * @copydoc insert
     * @tparam Arg Type of the key-value pair to insert into the container.
     */
    template<typename Arg>
    std::enable_if_t<std::is_constructible_v<value_type, Arg &&>, std::pair<iterator, bool>>
    insert(Arg &&value) {
        return insert_or_do_nothing(std::forward<Arg>(value).first, std::forward<Arg>(value).second);
    }

    /**
     * @brief Inserts elements into the container, if their keys do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Inserts an element into the container or assigns to the current
     * element if the key already exists.
     * @tparam Arg Type of the value to insert or assign.
     * @param key A key used both to look up and to insert if not found.
     * @param value A value to insert or assign.
     * @return A pair consisting of an iterator to the element and a bool
     * denoting whether the insertion took place.
     */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(const key_type &key, Arg &&value) {
        return insert_or_overwrite(key, std::forward<Arg>(value));
    }

    /*! @copydoc insert_or_assign */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(key_type &&key, Arg &&value) {
        return insert_or_overwrite(std::move(key), std::forward<Arg>(value));
    }

    /**
     * @brief Constructs an element in-place, if the key does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace([[maybe_unused]] Args &&...args) {
        if constexpr(sizeof...(Args) == 0u) {
            return insert_or_do_nothing(key_type{});
        } else if constexpr(sizeof...(Args) == 1u) {
            return insert_or_do_nothing(std::forward<Args>(args).first..., std::forward<Args>(args).second...);
        } else if constexpr(sizeof...(Args) == 2u) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(packed.first().size(), std::forward<Args>(args)...);
            const auto index = key_to_bucket(node.element.first);

            if(auto it = constrained_find(node.element.first, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.next, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Inserts in-place if the key does not exist, does nothing if the
     * key exists.
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param key A key used both to look up and to insert if not found.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(const key_type &key, Args &&...args) {
        return insert_or_do_nothing(key, std::forward<Args>(args)...);
    }

    /*! @copydoc try_emplace */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(key_type &&key, Args &&...args) {
        return insert_or_do_nothing(std::move(key), std::forward<Args>(args)...);
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(pos->first);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].element.first);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given key.
     * @param key A key value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const key_type &key) {
        for(size_type *curr = sparse.first().data() + key_to_bucket(key); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].next) {
            if(packed.second()(packed.first()[*curr].element.first, key)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].next;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_map &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Accesses a given element with bounds checking.
     * @param key A key of an element to find.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &at(const key_type &key) {
        auto it = find(key);
        ENTT_ASSERT(it != end(), "Invalid key");
        return it->second;
    }

    /*! @copydoc at */
    [[nodiscard]] const mapped_type &at(const key_type &key) const {
        auto it = find(key);
        ENTT_ASSERT(it != cend(), "Invalid key");
        return it->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](const key_type &key) {
        return insert_or_do_nothing(key).first->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](key_type &&key) {
        return insert_or_do_nothing(std::move(key)).first->second;
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const key_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given key.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const key_type &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const key_type &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Finds an element with a key that compares _equivalent_ to a given
     * key.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Returns a range containing all elements with a given key.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const key_type &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const key_type &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given key.
     * @tparam Other Type of an element to search for.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given key.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const key_type &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Checks if the container contains an element with a key that
     * compares _equivalent_ to a given value.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given key.
     * @param key The value of the key to examine.
     * @return The bucket for the given key.
     */
    [[nodiscard]] size_type bucket(const key_type &key) const {
        return key_to_bucket(key);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = key_to_bucket(packed.first()[pos].element.first);
                packed.first()[pos].next = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the keys.
     * @return The function used to hash the keys.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare keys for equality.
     * @return The function used to compare keys for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace std {

template<typename Key, typename Value, typename Allocator>
struct uses_allocator<entt::internal::dense_map_node<Key, Value>, Allocator>
    : std::true_type {};

} // namespace std

/**
 * Internal details not to be documented.
 * @endcond
 */

#endif

// #include "../container/dense_set.hpp"
#ifndef ENTT_CONTAINER_DENSE_SET_HPP
#define ENTT_CONTAINER_DENSE_SET_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"

// #include "../core/compressed_pair.hpp"

// #include "../core/memory.hpp"

// #include "../core/type_traits.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename It>
class dense_set_iterator final {
    template<typename>
    friend class dense_set_iterator;

public:
    using value_type = typename It::value_type::second_type;
    using pointer = const value_type *;
    using reference = const value_type &;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::random_access_iterator_tag;

    constexpr dense_set_iterator() noexcept
        : it{} {}

    constexpr dense_set_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_set_iterator(const dense_set_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_set_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_set_iterator operator++(int) noexcept {
        dense_set_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_set_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_set_iterator operator--(int) noexcept {
        dense_set_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_set_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_set_iterator operator+(const difference_type value) const noexcept {
        dense_set_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_set_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_set_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return it[value].second;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::addressof(it->second);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_set_iterator<ILhs> &, const dense_set_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_set_iterator<ILhs> &lhs, const dense_set_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_set_local_iterator final {
    template<typename>
    friend class dense_set_local_iterator;

public:
    using value_type = typename It::value_type::second_type;
    using pointer = const value_type *;
    using reference = const value_type &;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::forward_iterator_tag;

    constexpr dense_set_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_set_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_set_local_iterator(const dense_set_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_set_local_iterator &operator++() noexcept {
        return offset = it[offset].first, *this;
    }

    constexpr dense_set_local_iterator operator++(int) noexcept {
        dense_set_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return std::addressof(it[offset].second);
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return *operator->();
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_set_local_iterator<ILhs> &lhs, const dense_set_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_set_local_iterator<ILhs> &lhs, const dense_set_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for unique objects of a given type.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on its hash. Elements with the same hash code
 * appear in the same bucket.
 *
 * @tparam Type Value type of the associative container.
 * @tparam Hash Type of function to use to hash the values.
 * @tparam KeyEqual Type of function to use to compare the values for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_set {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = std::pair<std::size_t, Type>;
    using alloc_traits = std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t value_to_bucket(const Other &value) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(value)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &value, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(*it, value)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &value, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(*it, value)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other>
    [[nodiscard]] auto insert_or_do_nothing(Other &&value) {
        const auto index = value_to_bucket(value);

        if(auto it = constrained_find(value, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + value_to_bucket(packed.first().back().second);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].first) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Type;
    /*! @brief Value type of the container. */
    using value_type = Type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the elements. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the elements for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Random access iterator type. */
    using iterator = internal::dense_set_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant random access iterator type. */
    using const_iterator = internal::dense_set_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Forward iterator type. */
    using local_iterator = internal::dense_set_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant forward iterator type. */
    using const_local_iterator = internal::dense_set_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_set()
        : dense_set{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_set(const allocator_type &allocator)
        : dense_set{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_set(const size_type cnt, const allocator_type &allocator)
        : dense_set{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_set(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_set{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_set(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_set(const dense_set &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_set(const dense_set &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_set(dense_set &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_set(dense_set &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_set &operator=(const dense_set &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_set &operator=(dense_set &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if it does not exist.
     * @param value An element to insert into the container.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value));
    }

    /**
     * @brief Inserts elements into the container, if they do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Constructs an element in-place, if it does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace(Args &&...args) {
        if constexpr(((sizeof...(Args) == 1u) && ... && std::is_same_v<std::decay_t<Args>, value_type>)) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(std::piecewise_construct, std::make_tuple(packed.first().size()), std::forward_as_tuple(std::forward<Args>(args)...));
            const auto index = value_to_bucket(node.second);

            if(auto it = constrained_find(node.second, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.first, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(*pos);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].second);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given value.
     * @param value Value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const value_type &value) {
        for(size_type *curr = sparse.first().data() + value_to_bucket(value); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].first) {
            if(packed.second()(packed.first()[*curr].second, value)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].first;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_set &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Returns the number of elements matching a value (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const value_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given value.
     * @param value Value of an element to search for.
     * @return An iterator to an element with the given value. If no such
     * element is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const value_type &value) {
        return constrained_find(value, value_to_bucket(value));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const value_type &value) const {
        return constrained_find(value, value_to_bucket(value));
    }

    /**
     * @brief Finds an element that compares _equivalent_ to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return An iterator to an element with the given value. If no such
     * element is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &value) {
        return constrained_find(value, value_to_bucket(value));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &value) const {
        return constrained_find(value, value_to_bucket(value));
    }

    /**
     * @brief Returns a range containing all elements with a given value.
     * @param value Value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const value_type &value) {
        const auto it = find(value);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const value_type &value) const {
        const auto it = find(value);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &value) {
        const auto it = find(value);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &value) const {
        const auto it = find(value);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given value.
     * @param value Value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const value_type &value) const {
        return (find(value) != cend());
    }

    /**
     * @brief Checks if the container contains an element that compares
     * _equivalent_ to a given value.
     * @tparam Other Type of an element to search for.
     * @param value Value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &value) const {
        return (find(value) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given element.
     * @param value The value of the element to examine.
     * @return The bucket for the given element.
     */
    [[nodiscard]] size_type bucket(const value_type &value) const {
        return value_to_bucket(value);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = value_to_bucket(packed.first()[pos].second);
                packed.first()[pos].first = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the elements.
     * @return The function used to hash the elements.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare elements for equality.
     * @return The function used to compare elements for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

#endif

// #include "context.hpp"
#ifndef ENTT_META_CTX_HPP
#define ENTT_META_CTX_HPP

// #include "../container/dense_map.hpp"

// #include "../core/fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif


namespace entt {

class meta_ctx;

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct meta_type_node;

struct meta_context {
    dense_map<id_type, meta_type_node, identity> value{};

    static inline meta_context &from(meta_ctx &ctx);
    static inline const meta_context &from(const meta_ctx &ctx);
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @brief Disambiguation tag for constructors and the like. */
class meta_ctx_arg_t final {};

/*! @brief Constant of type meta_context_arg_t used to disambiguate calls. */
inline constexpr meta_ctx_arg_t meta_ctx_arg{};

/*! @brief Opaque meta context type. */
class meta_ctx: private internal::meta_context {
    /*! @brief Attorney idiom like model to access the base class. */
    friend struct internal::meta_context;
};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

inline internal::meta_context &internal::meta_context::from(meta_ctx &ctx) {
    return ctx;
}

inline const internal::meta_context &internal::meta_context::from(const meta_ctx &ctx) {
    return ctx;
}

/**
 * Internal details not to be documented.
 * @endcond
 */

} // namespace entt

#endif

// #include "meta.hpp"
#ifndef ENTT_META_META_HPP
#define ENTT_META_META_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/any.hpp"
#ifndef ENTT_CORE_ANY_HPP
#define ENTT_CORE_ANY_HPP

#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif

// #include "type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"
#ifndef ENTT_CORE_ATTRIBUTE_H
#define ENTT_CORE_ATTRIBUTE_H

#ifndef ENTT_EXPORT
#    if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
#        define ENTT_EXPORT __declspec(dllexport)
#        define ENTT_IMPORT __declspec(dllimport)
#        define ENTT_HIDDEN
#    elif defined __GNUC__ && __GNUC__ >= 4
#        define ENTT_EXPORT __attribute__((visibility("default")))
#        define ENTT_IMPORT __attribute__((visibility("default")))
#        define ENTT_HIDDEN __attribute__((visibility("hidden")))
#    else /* Unsupported compiler */
#        define ENTT_EXPORT
#        define ENTT_IMPORT
#        define ENTT_HIDDEN
#    endif
#endif

#ifndef ENTT_API
#    if defined ENTT_API_EXPORT
#        define ENTT_API ENTT_EXPORT
#    elif defined ENTT_API_IMPORT
#        define ENTT_API ENTT_IMPORT
#    else /* No API */
#        define ENTT_API
#    endif
#endif

#endif

// #include "fwd.hpp"

// #include "hashed_string.hpp"
#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP

#include <cstddef>
#include <cstdint>
// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename>
struct fnv1a_traits;

template<>
struct fnv1a_traits<std::uint32_t> {
    using type = std::uint32_t;
    static constexpr std::uint32_t offset = 2166136261;
    static constexpr std::uint32_t prime = 16777619;
};

template<>
struct fnv1a_traits<std::uint64_t> {
    using type = std::uint64_t;
    static constexpr std::uint64_t offset = 14695981039346656037ull;
    static constexpr std::uint64_t prime = 1099511628211ull;
};

template<typename Char>
struct basic_hashed_string {
    using value_type = Char;
    using size_type = std::size_t;
    using hash_type = id_type;

    const value_type *repr;
    size_type length;
    hash_type hash;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Zero overhead unique identifier.
 *
 * A hashed string is a compile-time tool that allows users to use
 * human-readable identifiers in the codebase while using their numeric
 * counterparts at runtime.<br/>
 * Because of that, a hashed string can also be used in constant expressions if
 * required.
 *
 * @warning
 * This class doesn't take ownership of user-supplied strings nor does it make a
 * copy of them.
 *
 * @tparam Char Character type.
 */
template<typename Char>
class basic_hashed_string: internal::basic_hashed_string<Char> {
    using base_type = internal::basic_hashed_string<Char>;
    using hs_traits = internal::fnv1a_traits<id_type>;

    struct const_wrapper {
        // non-explicit constructor on purpose
        constexpr const_wrapper(const Char *str) noexcept
            : repr{str} {}

        const Char *repr;
    };

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str) noexcept {
        base_type base{str, 0u, hs_traits::offset};

        for(; str[base.length]; ++base.length) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[base.length])) * hs_traits::prime;
        }

        return base;
    }

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str, const std::size_t len) noexcept {
        base_type base{str, len, hs_traits::offset};

        for(size_type pos{}; pos < len; ++pos) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[pos])) * hs_traits::prime;
        }

        return base;
    }

public:
    /*! @brief Character type. */
    using value_type = typename base_type::value_type;
    /*! @brief Unsigned integer type. */
    using size_type = typename base_type::size_type;
    /*! @brief Unsigned integer type. */
    using hash_type = typename base_type::hash_type;

    /**
     * @brief Returns directly the numeric representation of a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const value_type *str, const size_type len) noexcept {
        return basic_hashed_string{str, len};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     * @return The numeric representation of the string.
     */
    template<std::size_t N>
    [[nodiscard]] static constexpr hash_type value(const value_type (&str)[N]) noexcept {
        return basic_hashed_string{str};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @param wrapper Helps achieving the purpose by relying on overloading.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const_wrapper wrapper) noexcept {
        return basic_hashed_string{wrapper};
    }

    /*! @brief Constructs an empty hashed string. */
    constexpr basic_hashed_string() noexcept
        : base_type{} {}

    /**
     * @brief Constructs a hashed string from a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     */
    constexpr basic_hashed_string(const value_type *str, const size_type len) noexcept
        : base_type{helper(str, len)} {}

    /**
     * @brief Constructs a hashed string from an array of const characters.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     */
    template<std::size_t N>
    constexpr basic_hashed_string(const value_type (&str)[N]) noexcept
        : base_type{helper(str)} {}

    /**
     * @brief Explicit constructor on purpose to avoid constructing a hashed
     * string directly from a `const value_type *`.
     *
     * @warning
     * The lifetime of the string is not extended nor is it copied.
     *
     * @param wrapper Helps achieving the purpose by relying on overloading.
     */
    explicit constexpr basic_hashed_string(const_wrapper wrapper) noexcept
        : base_type{helper(wrapper.repr)} {}

    /**
     * @brief Returns the size a hashed string.
     * @return The size of the hashed string.
     */
    [[nodiscard]] constexpr size_type size() const noexcept {
        return base_type::length;
    }

    /**
     * @brief Returns the human-readable representation of a hashed string.
     * @return The string used to initialize the hashed string.
     */
    [[nodiscard]] constexpr const value_type *data() const noexcept {
        return base_type::repr;
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr hash_type value() const noexcept {
        return base_type::hash;
    }

    /*! @copydoc data */
    [[nodiscard]] constexpr operator const value_type *() const noexcept {
        return data();
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr operator hash_type() const noexcept {
        return value();
    }
};

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @param str Human-readable identifier.
 * @param len Length of the string to hash.
 */
template<typename Char>
basic_hashed_string(const Char *str, const std::size_t len) -> basic_hashed_string<Char>;

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @tparam N Number of characters of the identifier.
 * @param str Human-readable identifier.
 */
template<typename Char, std::size_t N>
basic_hashed_string(const Char (&str)[N]) -> basic_hashed_string<Char>;

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings are identical, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator==(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() == rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings differ, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than the second, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() < rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs < rhs);
}

/*! @brief Aliases for common character types. */
using hashed_string = basic_hashed_string<char>;

/*! @brief Aliases for common character types. */
using hashed_wstring = basic_hashed_string<wchar_t>;

inline namespace literals {

/**
 * @brief User defined literal for hashed strings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed string.
 */
[[nodiscard]] constexpr hashed_string operator"" _hs(const char *str, std::size_t) noexcept {
    return hashed_string{str};
}

/**
 * @brief User defined literal for hashed wstrings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed wstring.
 */
[[nodiscard]] constexpr hashed_wstring operator"" _hws(const wchar_t *str, std::size_t) noexcept {
    return hashed_wstring{str};
}

} // namespace literals

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

enum class any_operation : std::uint8_t {
    copy,
    move,
    transfer,
    assign,
    destroy,
    compare,
    get
};

enum class any_policy : std::uint8_t {
    owner,
    ref,
    cref
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A SBO friendly, type-safe container for single values of any type.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 */
template<std::size_t Len, std::size_t Align>
class basic_any {
    using operation = internal::any_operation;
    using policy = internal::any_policy;
    using vtable_type = const void *(const operation, const basic_any &, const void *);

    struct storage_type {
        alignas(Align) std::byte data[Len + !Len];
    };

    template<typename Type>
    static constexpr bool in_situ = Len && alignof(Type) <= Align && sizeof(Type) <= Len &&std::is_nothrow_move_constructible_v<Type>;

    template<typename Type>
    static const void *basic_vtable(const operation op, const basic_any &value, const void *other) {
        static_assert(!std::is_same_v<Type, void> && std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, Type>, "Invalid type");
        const Type *element = nullptr;

        if constexpr(in_situ<Type>) {
            element = value.owner() ? reinterpret_cast<const Type *>(&value.storage) : static_cast<const Type *>(value.instance);
        } else {
            element = static_cast<const Type *>(value.instance);
        }

        switch(op) {
        case operation::copy:
            if constexpr(std::is_copy_constructible_v<Type>) {
                static_cast<basic_any *>(const_cast<void *>(other))->initialize<Type>(*element);
            }
            break;
        case operation::move:
            if constexpr(in_situ<Type>) {
                if(value.owner()) {
                    return new(&static_cast<basic_any *>(const_cast<void *>(other))->storage) Type{std::move(*const_cast<Type *>(element))};
                }
            }

            return (static_cast<basic_any *>(const_cast<void *>(other))->instance = std::exchange(const_cast<basic_any &>(value).instance, nullptr));
        case operation::transfer:
            if constexpr(std::is_move_assignable_v<Type>) {
                *const_cast<Type *>(element) = std::move(*static_cast<Type *>(const_cast<void *>(other)));
                return other;
            }
            [[fallthrough]];
        case operation::assign:
            if constexpr(std::is_copy_assignable_v<Type>) {
                *const_cast<Type *>(element) = *static_cast<const Type *>(other);
                return other;
            }
            break;
        case operation::destroy:
            if constexpr(in_situ<Type>) {
                element->~Type();
            } else if constexpr(std::is_array_v<Type>) {
                delete[] element;
            } else {
                delete element;
            }
            break;
        case operation::compare:
            if constexpr(!std::is_function_v<Type> && !std::is_array_v<Type> && is_equality_comparable_v<Type>) {
                return *element == *static_cast<const Type *>(other) ? other : nullptr;
            } else {
                return (element == other) ? other : nullptr;
            }
        case operation::get:
            return element;
        }

        return nullptr;
    }

    template<typename Type, typename... Args>
    void initialize([[maybe_unused]] Args &&...args) {
        info = &type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();

        if constexpr(!std::is_void_v<Type>) {
            vtable = basic_vtable<std::remove_cv_t<std::remove_reference_t<Type>>>;

            if constexpr(std::is_lvalue_reference_v<Type>) {
                static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
                mode = std::is_const_v<std::remove_reference_t<Type>> ? policy::cref : policy::ref;
                instance = (std::addressof(args), ...);
            } else if constexpr(in_situ<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                if constexpr(sizeof...(Args) != 0u && std::is_aggregate_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                    new(&storage) std::remove_cv_t<std::remove_reference_t<Type>>{std::forward<Args>(args)...};
                } else {
                    new(&storage) std::remove_cv_t<std::remove_reference_t<Type>>(std::forward<Args>(args)...);
                }
            } else {
                if constexpr(sizeof...(Args) != 0u && std::is_aggregate_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                    instance = new std::remove_cv_t<std::remove_reference_t<Type>>{std::forward<Args>(args)...};
                } else {
                    instance = new std::remove_cv_t<std::remove_reference_t<Type>>(std::forward<Args>(args)...);
                }
            }
        }
    }

    basic_any(const basic_any &other, const policy pol) noexcept
        : instance{other.data()},
          info{other.info},
          vtable{other.vtable},
          mode{pol} {}

public:
    /*! @brief Size of the internal storage. */
    static constexpr auto length = Len;
    /*! @brief Alignment requirement. */
    static constexpr auto alignment = Align;

    /*! @brief Default constructor. */
    constexpr basic_any() noexcept
        : basic_any{std::in_place_type<void>} {}

    /**
     * @brief Constructs a wrapper by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit basic_any(std::in_place_type_t<Type>, Args &&...args)
        : instance{},
          info{},
          vtable{},
          mode{policy::owner} {
        initialize<Type>(std::forward<Args>(args)...);
    }

    /**
     * @brief Constructs a wrapper from a given value.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
    basic_any(Type &&value)
        : basic_any{std::in_place_type<std::decay_t<Type>>, std::forward<Type>(value)} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    basic_any(const basic_any &other)
        : basic_any{} {
        if(other.vtable) {
            other.vtable(operation::copy, other, this);
        }
    }

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_any(basic_any &&other) noexcept
        : instance{},
          info{other.info},
          vtable{other.vtable},
          mode{other.mode} {
        if(other.vtable) {
            other.vtable(operation::move, other, this);
        }
    }

    /*! @brief Frees the internal storage, whatever it means. */
    ~basic_any() {
        if(vtable && owner()) {
            vtable(operation::destroy, *this, nullptr);
        }
    }

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This any object.
     */
    basic_any &operator=(const basic_any &other) {
        reset();

        if(other.vtable) {
            other.vtable(operation::copy, other, this);
        }

        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This any object.
     */
    basic_any &operator=(basic_any &&other) noexcept {
        reset();

        if(other.vtable) {
            other.vtable(operation::move, other, this);
            info = other.info;
            vtable = other.vtable;
            mode = other.mode;
        }

        return *this;
    }

    /**
     * @brief Value assignment operator.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     * @return This any object.
     */
    template<typename Type>
    std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any &>
    operator=(Type &&value) {
        emplace<std::decay_t<Type>>(std::forward<Type>(value));
        return *this;
    }

    /**
     * @brief Returns the object type if any, `type_id<void>()` otherwise.
     * @return The object type if any, `type_id<void>()` otherwise.
     */
    [[nodiscard]] const type_info &type() const noexcept {
        return *info;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data() const noexcept {
        return vtable ? vtable(operation::get, *this, nullptr) : nullptr;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @param req Expected type.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data(const type_info &req) const noexcept {
        return *info == req ? data() : nullptr;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] void *data() noexcept {
        return mode == policy::cref ? nullptr : const_cast<void *>(std::as_const(*this).data());
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @param req Expected type.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] void *data(const type_info &req) noexcept {
        return mode == policy::cref ? nullptr : const_cast<void *>(std::as_const(*this).data(req));
    }

    /**
     * @brief Replaces the contained object by creating a new instance directly.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    void emplace(Args &&...args) {
        reset();
        initialize<Type>(std::forward<Args>(args)...);
    }

    /**
     * @brief Assigns a value to the contained object without replacing it.
     * @param other The value to assign to the contained object.
     * @return True in case of success, false otherwise.
     */
    bool assign(const basic_any &other) {
        if(vtable && mode != policy::cref && *info == *other.info) {
            return (vtable(operation::assign, *this, other.data()) != nullptr);
        }

        return false;
    }

    /*! @copydoc assign */
    bool assign(basic_any &&other) {
        if(vtable && mode != policy::cref && *info == *other.info) {
            if(auto *val = other.data(); val) {
                return (vtable(operation::transfer, *this, val) != nullptr);
            } else {
                return (vtable(operation::assign, *this, std::as_const(other).data()) != nullptr);
            }
        }

        return false;
    }

    /*! @brief Destroys contained object */
    void reset() {
        if(vtable && owner()) {
            vtable(operation::destroy, *this, nullptr);
        }

        // unnecessary but it helps to detect nasty bugs
        ENTT_ASSERT((instance = nullptr) == nullptr, "");
        info = &type_id<void>();
        vtable = nullptr;
        mode = policy::owner;
    }

    /**
     * @brief Returns false if a wrapper is empty, true otherwise.
     * @return False if the wrapper is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return vtable != nullptr;
    }

    /**
     * @brief Checks if two wrappers differ in their content.
     * @param other Wrapper with which to compare.
     * @return False if the two objects differ in their content, true otherwise.
     */
    [[nodiscard]] bool operator==(const basic_any &other) const noexcept {
        if(vtable && *info == *other.info) {
            return (vtable(operation::compare, *this, other.data()) != nullptr);
        }

        return (!vtable && !other.vtable);
    }

    /**
     * @brief Checks if two wrappers differ in their content.
     * @param other Wrapper with which to compare.
     * @return True if the two objects differ in their content, false otherwise.
     */
    [[nodiscard]] bool operator!=(const basic_any &other) const noexcept {
        return !(*this == other);
    }

    /**
     * @brief Aliasing constructor.
     * @return A wrapper that shares a reference to an unmanaged object.
     */
    [[nodiscard]] basic_any as_ref() noexcept {
        return basic_any{*this, (mode == policy::cref ? policy::cref : policy::ref)};
    }

    /*! @copydoc as_ref */
    [[nodiscard]] basic_any as_ref() const noexcept {
        return basic_any{*this, policy::cref};
    }

    /**
     * @brief Returns true if a wrapper owns its object, false otherwise.
     * @return True if the wrapper owns its object, false otherwise.
     */
    [[nodiscard]] bool owner() const noexcept {
        return (mode == policy::owner);
    }

private:
    union {
        const void *instance;
        storage_type storage;
    };
    const type_info *info;
    vtable_type *vtable;
    policy mode;
};

/**
 * @brief Performs type-safe access to the contained object.
 * @tparam Type Type to which conversion is required.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Alignment requirement.
 * @param data Target any object.
 * @return The element converted to the requested type.
 */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(const basic_any<Len, Align> &data) noexcept {
    const auto *const instance = any_cast<std::remove_reference_t<Type>>(&data);
    ENTT_ASSERT(instance, "Invalid instance");
    return static_cast<Type>(*instance);
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(basic_any<Len, Align> &data) noexcept {
    // forces const on non-reference types to make them work also with wrappers for const references
    auto *const instance = any_cast<std::remove_reference_t<const Type>>(&data);
    ENTT_ASSERT(instance, "Invalid instance");
    return static_cast<Type>(*instance);
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(basic_any<Len, Align> &&data) noexcept {
    if constexpr(std::is_copy_constructible_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
        if(auto *const instance = any_cast<std::remove_reference_t<Type>>(&data); instance) {
            return static_cast<Type>(std::move(*instance));
        } else {
            return any_cast<Type>(data);
        }
    } else {
        auto *const instance = any_cast<std::remove_reference_t<Type>>(&data);
        ENTT_ASSERT(instance, "Invalid instance");
        return static_cast<Type>(std::move(*instance));
    }
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
const Type *any_cast(const basic_any<Len, Align> *data) noexcept {
    const auto &info = type_id<std::remove_cv_t<Type>>();
    return static_cast<const Type *>(data->data(info));
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type *any_cast(basic_any<Len, Align> *data) noexcept {
    if constexpr(std::is_const_v<Type>) {
        // last attempt to make wrappers for const references return their values
        return any_cast<Type>(&std::as_const(*data));
    } else {
        const auto &info = type_id<std::remove_cv_t<Type>>();
        return static_cast<Type *>(data->data(info));
    }
}

/**
 * @brief Constructs a wrapper from a given type, passing it all arguments.
 * @tparam Type Type of object to use to initialize the wrapper.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 * @tparam Args Types of arguments to use to construct the new instance.
 * @param args Parameters to use to construct the instance.
 * @return A properly initialized wrapper for an object of the given type.
 */
template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
basic_any<Len, Align> make_any(Args &&...args) {
    return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
}

/**
 * @brief Forwards its argument and avoids copies for lvalue references.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 * @tparam Type Type of argument to use to construct the new instance.
 * @param value Parameter to use to construct the instance.
 * @return A properly initialized and not necessarily owning wrapper.
 */
template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
basic_any<Len, Align> forward_as_any(Type &&value) {
    return basic_any<Len, Align>{std::in_place_type<Type &&>, std::forward<Type>(value)};
}

} // namespace entt

#endif

// #include "../core/fwd.hpp"

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"

// #include "fwd.hpp"

// #include "hashed_string.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "../core/utility.hpp"

// #include "../locator/locator.hpp"
#ifndef ENTT_LOCATOR_LOCATOR_HPP
#define ENTT_LOCATOR_LOCATOR_HPP

#include <memory>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif


namespace entt {

/**
 * @brief Service locator, nothing more.
 *
 * A service locator is used to do what it promises: locate services.<br/>
 * Usually service locators are tightly bound to the services they expose and
 * thus it's hard to define a general purpose class to do that. This tiny class
 * tries to fill the gap and to get rid of the burden of defining a different
 * specific locator for each application.
 *
 * @note
 * Users shouldn't retain references to a service. The recommended way is to
 * retrieve the service implementation currently set each and every time the
 * need for it arises. The risk is to incur in unexpected behaviors otherwise.
 *
 * @tparam Service Service type.
 */
template<typename Service>
class locator final {
    class service_handle {
        friend class locator<Service>;
        std::shared_ptr<Service> value{};
    };

public:
    /*! @brief Service type. */
    using type = Service;
    /*! @brief Service node type. */
    using node_type = service_handle;

    /*! @brief Default constructor, deleted on purpose. */
    locator() = delete;
    /*! @brief Default destructor, deleted on purpose. */
    ~locator() = delete;

    /**
     * @brief Checks whether a service locator contains a value.
     * @return True if the service locator contains a value, false otherwise.
     */
    [[nodiscard]] static bool has_value() noexcept {
        return (service != nullptr);
    }

    /**
     * @brief Returns a reference to a valid service, if any.
     *
     * @warning
     * Invoking this function can result in undefined behavior if the service
     * hasn't been set yet.
     *
     * @return A reference to the service currently set, if any.
     */
    [[nodiscard]] static Service &value() noexcept {
        ENTT_ASSERT(has_value(), "Service not available");
        return *service;
    }

    /**
     * @brief Returns a service if available or sets it from a fallback type.
     *
     * Arguments are used only if a service doesn't already exist. In all other
     * cases, they are discarded.
     *
     * @tparam Args Types of arguments to use to construct the fallback service.
     * @tparam Impl Fallback service type.
     * @param args Parameters to use to construct the fallback service.
     * @return A reference to a valid service.
     */
    template<typename Impl = Service, typename... Args>
    [[nodiscard]] static Service &value_or(Args &&...args) {
        return service ? *service : emplace<Impl>(std::forward<Args>(args)...);
    }

    /**
     * @brief Sets or replaces a service.
     * @tparam Impl Service type.
     * @tparam Args Types of arguments to use to construct the service.
     * @param args Parameters to use to construct the service.
     * @return A reference to a valid service.
     */
    template<typename Impl = Service, typename... Args>
    static Service &emplace(Args &&...args) {
        service = std::make_shared<Impl>(std::forward<Args>(args)...);
        return *service;
    }

    /**
     * @brief Sets or replaces a service using a given allocator.
     * @tparam Impl Service type.
     * @tparam Allocator Type of allocator used to manage memory and elements.
     * @tparam Args Types of arguments to use to construct the service.
     * @param alloc The allocator to use.
     * @param args Parameters to use to construct the service.
     * @return A reference to a valid service.
     */
    template<typename Impl = Service, typename Allocator, typename... Args>
    static Service &allocate_emplace(Allocator alloc, Args &&...args) {
        service = std::allocate_shared<Impl>(alloc, std::forward<Args>(args)...);
        return *service;
    }

    /**
     * @brief Returns a handle to the underlying service.
     * @return A handle to the underlying service.
     */
    static node_type handle() noexcept {
        node_type node{};
        node.value = service;
        return node;
    }

    /**
     * @brief Resets or replaces a service.
     * @param other Optional handle with which to replace the service.
     */
    static void reset(const node_type &other = {}) noexcept {
        service = other.value;
    }

private:
    // std::shared_ptr because of its type erased allocator which is useful here
    inline static std::shared_ptr<Service> service{};
};

} // namespace entt

#endif

// #include "adl_pointer.hpp"
#ifndef ENTT_META_ADL_POINTER_HPP
#define ENTT_META_ADL_POINTER_HPP

namespace entt {

/**
 * @brief ADL based lookup function for dereferencing meta pointer-like types.
 * @tparam Type Element type.
 * @param value A pointer-like object.
 * @return The value returned from the dereferenced pointer.
 */
template<typename Type>
decltype(auto) dereference_meta_pointer_like(const Type &value) {
    return *value;
}

/**
 * @brief Fake ADL based lookup function for meta pointer-like types.
 * @tparam Type Element type.
 */
template<typename Type>
struct adl_meta_pointer_like {
    /**
     * @brief Uses the default ADL based lookup method to resolve the call.
     * @param value A pointer-like object.
     * @return The value returned from the dereferenced pointer.
     */
    static decltype(auto) dereference(const Type &value) {
        return dereference_meta_pointer_like(value);
    }
};

} // namespace entt

#endif

// #include "context.hpp"

// #include "fwd.hpp"
#ifndef ENTT_META_FWD_HPP
#define ENTT_META_FWD_HPP

namespace entt {

class meta_sequence_container;

class meta_associative_container;

class meta_any;

struct meta_handle;

struct meta_prop;

struct meta_data;

struct meta_func;

class meta_type;

} // namespace entt

#endif

// #include "node.hpp"
#ifndef ENTT_META_NODE_HPP
#define ENTT_META_NODE_HPP

#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../container/dense_map.hpp"

// #include "../core/attribute.h"
#ifndef ENTT_CORE_ATTRIBUTE_H
#define ENTT_CORE_ATTRIBUTE_H

#ifndef ENTT_EXPORT
#    if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
#        define ENTT_EXPORT __declspec(dllexport)
#        define ENTT_IMPORT __declspec(dllimport)
#        define ENTT_HIDDEN
#    elif defined __GNUC__ && __GNUC__ >= 4
#        define ENTT_EXPORT __attribute__((visibility("default")))
#        define ENTT_IMPORT __attribute__((visibility("default")))
#        define ENTT_HIDDEN __attribute__((visibility("hidden")))
#    else /* Unsupported compiler */
#        define ENTT_EXPORT
#        define ENTT_IMPORT
#        define ENTT_HIDDEN
#    endif
#endif

#ifndef ENTT_API
#    if defined ENTT_API_EXPORT
#        define ENTT_API ENTT_EXPORT
#    elif defined ENTT_API_IMPORT
#        define ENTT_API ENTT_IMPORT
#    else /* No API */
#        define ENTT_API
#    endif
#endif

#endif

// #include "../core/enum.hpp"
#ifndef ENTT_CORE_ENUM_HPP
#define ENTT_CORE_ENUM_HPP

#include <type_traits>

namespace entt {

/**
 * @brief Enable bitmask support for enum classes.
 * @tparam Type The enum type for which to enable bitmask support.
 */
template<typename Type, typename = void>
struct enum_as_bitmask: std::false_type {};

/*! @copydoc enum_as_bitmask */
template<typename Type>
struct enum_as_bitmask<Type, std::void_t<decltype(Type::_entt_enum_as_bitmask)>>: std::is_enum<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The enum class type for which to enable bitmask support.
 */
template<typename Type>
inline constexpr bool enum_as_bitmask_v = enum_as_bitmask<Type>::value;

} // namespace entt

/**
 * @brief Operator available for enums for which bitmask support is enabled.
 * @tparam Type Enum class type.
 * @param lhs The first value to use.
 * @param rhs The second value to use.
 * @return The result of invoking the operator on the underlying types of the
 * two values provided.
 */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type>
operator|(const Type lhs, const Type rhs) noexcept {
    return static_cast<Type>(static_cast<std::underlying_type_t<Type>>(lhs) | static_cast<std::underlying_type_t<Type>>(rhs));
}

/*! @copydoc operator| */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type>
operator&(const Type lhs, const Type rhs) noexcept {
    return static_cast<Type>(static_cast<std::underlying_type_t<Type>>(lhs) & static_cast<std::underlying_type_t<Type>>(rhs));
}

/*! @copydoc operator| */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type>
operator^(const Type lhs, const Type rhs) noexcept {
    return static_cast<Type>(static_cast<std::underlying_type_t<Type>>(lhs) ^ static_cast<std::underlying_type_t<Type>>(rhs));
}

/**
 * @brief Operator available for enums for which bitmask support is enabled.
 * @tparam Type Enum class type.
 * @param value The value to use.
 * @return The result of invoking the operator on the underlying types of the
 * value provided.
 */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type>
operator~(const Type value) noexcept {
    return static_cast<Type>(~static_cast<std::underlying_type_t<Type>>(value));
}

/*! @copydoc operator~ */
template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, bool>
operator!(const Type value) noexcept {
    return !static_cast<std::underlying_type_t<Type>>(value);
}

/*! @copydoc operator| */
template<typename Type>
constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type &>
operator|=(Type &lhs, const Type rhs) noexcept {
    return (lhs = (lhs | rhs));
}

/*! @copydoc operator| */
template<typename Type>
constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type &>
operator&=(Type &lhs, const Type rhs) noexcept {
    return (lhs = (lhs & rhs));
}

/*! @copydoc operator| */
template<typename Type>
constexpr std::enable_if_t<entt::enum_as_bitmask_v<Type>, Type &>
operator^=(Type &lhs, const Type rhs) noexcept {
    return (lhs = (lhs ^ rhs));
}

#endif

// #include "../core/fwd.hpp"

// #include "../core/type_info.hpp"

// #include "../core/type_traits.hpp"

// #include "../core/utility.hpp"

// #include "context.hpp"

// #include "type_traits.hpp"
#ifndef ENTT_META_TYPE_TRAITS_HPP
#define ENTT_META_TYPE_TRAITS_HPP

#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Traits class template to be specialized to enable support for meta
 * template information.
 */
template<typename>
struct meta_template_traits;

/**
 * @brief Traits class template to be specialized to enable support for meta
 * sequence containers.
 */
template<typename>
struct meta_sequence_container_traits;

/**
 * @brief Traits class template to be specialized to enable support for meta
 * associative containers.
 */
template<typename>
struct meta_associative_container_traits;

/**
 * @brief Provides the member constant `value` to true if a given type is a
 * pointer-like type from the point of view of the meta system, false otherwise.
 * @tparam Type Potentially pointer-like type.
 */
template<typename>
struct is_meta_pointer_like: std::false_type {};

/**
 * @brief Partial specialization to ensure that const pointer-like types are
 * also accepted.
 * @tparam Type Potentially pointer-like type.
 */
template<typename Type>
struct is_meta_pointer_like<const Type>: is_meta_pointer_like<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type Potentially pointer-like type.
 */
template<typename Type>
inline constexpr auto is_meta_pointer_like_v = is_meta_pointer_like<Type>::value;

} // namespace entt

#endif


namespace entt {

class meta_any;
class meta_type;
struct meta_handle;

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

enum class meta_traits : std::uint32_t {
    is_none = 0x0000,
    is_const = 0x0001,
    is_static = 0x0002,
    is_arithmetic = 0x0004,
    is_integral = 0x0008,
    is_signed = 0x0010,
    is_array = 0x0020,
    is_enum = 0x0040,
    is_class = 0x0080,
    is_meta_pointer_like = 0x0100,
    is_meta_sequence_container = 0x0200,
    is_meta_associative_container = 0x0400,
    _entt_enum_as_bitmask
};

struct meta_type_node;

struct meta_prop_node {
    meta_type_node (*type)(const meta_context &) noexcept {};
    std::shared_ptr<void> value{};
};

struct meta_base_node {
    meta_type_node (*type)(const meta_context &) noexcept {};
    const void *(*cast)(const void *) noexcept {};
};

struct meta_conv_node {
    meta_any (*conv)(const meta_ctx &, const void *){};
};

struct meta_ctor_node {
    using size_type = std::size_t;

    size_type arity{0u};
    meta_type (*arg)(const meta_ctx &, const size_type) noexcept {};
    meta_any (*invoke)(const meta_ctx &, meta_any *const){};
};

struct meta_dtor_node {
    void (*dtor)(void *){};
};

struct meta_data_node {
    using size_type = std::size_t;

    meta_traits traits{meta_traits::is_none};
    size_type arity{0u};
    meta_type_node (*type)(const meta_context &) noexcept {};
    meta_type (*arg)(const meta_ctx &, const size_type) noexcept {};
    bool (*set)(meta_handle, meta_any){};
    meta_any (*get)(const meta_ctx &, meta_handle){};
    dense_map<id_type, meta_prop_node, identity> prop{};
};

struct meta_func_node {
    using size_type = std::size_t;

    meta_traits traits{meta_traits::is_none};
    size_type arity{0u};
    meta_type_node (*ret)(const meta_context &) noexcept {};
    meta_type (*arg)(const meta_ctx &, const size_type) noexcept {};
    meta_any (*invoke)(const meta_ctx &, meta_handle, meta_any *const){};
    std::shared_ptr<meta_func_node> next{};
    dense_map<id_type, meta_prop_node, identity> prop{};
};

struct meta_template_node {
    using size_type = std::size_t;

    size_type arity{0u};
    meta_type_node (*type)(const meta_context &) noexcept {};
    meta_type_node (*arg)(const meta_context &, const size_type) noexcept {};
};

struct meta_type_descriptor {
    dense_map<id_type, meta_ctor_node, identity> ctor{};
    dense_map<id_type, meta_base_node, identity> base{};
    dense_map<id_type, meta_conv_node, identity> conv{};
    dense_map<id_type, meta_data_node, identity> data{};
    dense_map<id_type, meta_func_node, identity> func{};
    dense_map<id_type, meta_prop_node, identity> prop{};
};

struct meta_type_node {
    using size_type = std::size_t;

    const type_info *info{};
    id_type id{};
    meta_traits traits{meta_traits::is_none};
    size_type size_of{0u};
    meta_type_node (*resolve)(const meta_context &) noexcept {};
    meta_type_node (*remove_pointer)(const meta_context &) noexcept {};
    meta_any (*default_constructor)(const meta_ctx &){};
    double (*conversion_helper)(void *, const void *){};
    meta_any (*from_void)(const meta_ctx &, void *, const void *){};
    meta_template_node templ{};
    meta_dtor_node dtor{};
    std::shared_ptr<meta_type_descriptor> details{};
};

template<typename Type>
meta_type_node resolve(const meta_context &) noexcept;

template<typename... Args>
[[nodiscard]] auto meta_arg_node(const meta_context &context, type_list<Args...>, [[maybe_unused]] const std::size_t index) noexcept {
    [[maybe_unused]] std::size_t pos{};
    meta_type_node (*value)(const meta_context &) noexcept = nullptr;
    ((value = (pos++ == index ? &resolve<std::remove_cv_t<std::remove_reference_t<Args>>> : value)), ...);
    ENTT_ASSERT(value != nullptr, "Out of bounds");
    return value(context);
}

[[nodiscard]] inline const void *try_cast(const meta_context &context, const meta_type_node &from, const meta_type_node &to, const void *instance) noexcept {
    if(from.info && to.info && *from.info == *to.info) {
        return instance;
    }

    if(from.details) {
        for(auto &&curr: from.details->base) {
            if(const void *elem = try_cast(context, curr.second.type(context), to, curr.second.cast(instance)); elem) {
                return elem;
            }
        }
    }

    return nullptr;
}

[[nodiscard]] inline const meta_type_node *try_resolve(const meta_context &context, const type_info &info) noexcept {
    const auto it = context.value.find(info.hash());
    return it != context.value.end() ? &it->second : nullptr;
}

template<typename Type>
[[nodiscard]] meta_type_node resolve(const meta_context &context) noexcept {
    static_assert(std::is_same_v<Type, std::remove_const_t<std::remove_reference_t<Type>>>, "Invalid type");

    if(auto *elem = try_resolve(context, type_id<Type>()); elem) {
        return *elem;
    }

    meta_type_node node{
        &type_id<Type>(),
        type_id<Type>().hash(),
        (std::is_arithmetic_v<Type> ? meta_traits::is_arithmetic : meta_traits::is_none)
            | (std::is_integral_v<Type> ? meta_traits::is_integral : meta_traits::is_none)
            | (std::is_signed_v<Type> ? meta_traits::is_signed : meta_traits::is_none)
            | (std::is_array_v<Type> ? meta_traits::is_array : meta_traits::is_none)
            | (std::is_enum_v<Type> ? meta_traits::is_enum : meta_traits::is_none)
            | (std::is_class_v<Type> ? meta_traits::is_class : meta_traits::is_none)
            | (is_meta_pointer_like_v<Type> ? meta_traits::is_meta_pointer_like : meta_traits::is_none)
            | (is_complete_v<meta_sequence_container_traits<Type>> ? meta_traits::is_meta_sequence_container : meta_traits::is_none)
            | (is_complete_v<meta_associative_container_traits<Type>> ? meta_traits::is_meta_associative_container : meta_traits::is_none),
        size_of_v<Type>,
        &resolve<Type>,
        &resolve<std::remove_cv_t<std::remove_pointer_t<Type>>>};

    if constexpr(std::is_default_constructible_v<Type>) {
        node.default_constructor = +[](const meta_ctx &ctx) {
            return meta_any{ctx, std::in_place_type<Type>};
        };
    }

    if constexpr(std::is_arithmetic_v<Type>) {
        node.conversion_helper = +[](void *bin, const void *value) {
            return bin ? static_cast<double>(*static_cast<Type *>(bin) = static_cast<Type>(*static_cast<const double *>(value))) : static_cast<double>(*static_cast<const Type *>(value));
        };
    } else if constexpr(std::is_enum_v<Type>) {
        node.conversion_helper = +[](void *bin, const void *value) {
            return bin ? static_cast<double>(*static_cast<Type *>(bin) = static_cast<Type>(static_cast<std::underlying_type_t<Type>>(*static_cast<const double *>(value)))) : static_cast<double>(*static_cast<const Type *>(value));
        };
    }

    if constexpr(!std::is_same_v<Type, void> && !std::is_function_v<Type>) {
        node.from_void = +[](const meta_ctx &ctx, void *element, const void *as_const) {
            if(element) {
                return meta_any{ctx, std::in_place_type<std::decay_t<Type> &>, *static_cast<std::decay_t<Type> *>(element)};
            }

            return meta_any{ctx, std::in_place_type<const std::decay_t<Type> &>, *static_cast<const std::decay_t<Type> *>(as_const)};
        };
    }

    if constexpr(is_complete_v<meta_template_traits<Type>>) {
        node.templ = meta_template_node{
            meta_template_traits<Type>::args_type::size,
            &resolve<typename meta_template_traits<Type>::class_type>,
            +[](const meta_context &area, const std::size_t index) noexcept { return meta_arg_node(area, typename meta_template_traits<Type>::args_type{}, index); }};
    }

    return node;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

} // namespace entt

#endif

// #include "range.hpp"
#ifndef ENTT_META_RANGE_HPP
#define ENTT_META_RANGE_HPP

#include <cstddef>
#include <iterator>
#include <utility>
// #include "../core/fwd.hpp"

// #include "../core/iterator.hpp"

// #include "context.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, typename It>
struct meta_range_iterator final {
    using difference_type = std::ptrdiff_t;
    using value_type = std::pair<id_type, Type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    meta_range_iterator() noexcept
        : it{},
          ctx{} {}

    meta_range_iterator(const meta_ctx &area, const It iter) noexcept
        : it{iter},
          ctx{&area} {}

    meta_range_iterator &operator++() noexcept {
        return ++it, *this;
    }

    meta_range_iterator operator++(int) noexcept {
        meta_range_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr meta_range_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr meta_range_iterator operator--(int) noexcept {
        meta_range_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr meta_range_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr meta_range_iterator operator+(const difference_type value) const noexcept {
        meta_range_iterator copy = *this;
        return (copy += value);
    }

    constexpr meta_range_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr meta_range_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].first, Type{*ctx, it[value].second}};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->first, Type{*ctx, it->second}};
    }

    template<typename... Args>
    friend constexpr std::ptrdiff_t operator-(const meta_range_iterator<Args...> &, const meta_range_iterator<Args...> &) noexcept;

    template<typename... Args>
    friend constexpr bool operator==(const meta_range_iterator<Args...> &, const meta_range_iterator<Args...> &) noexcept;

    template<typename... Args>
    friend constexpr bool operator<(const meta_range_iterator<Args...> &, const meta_range_iterator<Args...> &) noexcept;

private:
    It it;
    const meta_ctx *ctx;
};

template<typename... Args>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename... Args>
[[nodiscard]] constexpr bool operator==(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename... Args>
[[nodiscard]] constexpr bool operator!=(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename... Args>
[[nodiscard]] constexpr bool operator<(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename... Args>
[[nodiscard]] constexpr bool operator>(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return rhs < lhs;
}

template<typename... Args>
[[nodiscard]] constexpr bool operator<=(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename... Args>
[[nodiscard]] constexpr bool operator>=(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return !(lhs < rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Iterable range to use to iterate all types of meta objects.
 * @tparam Type Type of meta objects returned.
 * @tparam It Type of forward iterator.
 */
template<typename Type, typename It>
using meta_range = iterable_adaptor<internal::meta_range_iterator<Type, It>>;

} // namespace entt

#endif

// #include "type_traits.hpp"


namespace entt {

class meta_any;
class meta_type;

/*! @brief Proxy object for sequence containers. */
class meta_sequence_container {
    class meta_iterator;

public:
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Meta iterator type. */
    using iterator = meta_iterator;

    /**
     * @brief Context aware constructor.
     * @param area The context from which to search for meta types.
     */
    meta_sequence_container(const meta_ctx &area = locator<meta_ctx>::value_or()) noexcept
        : ctx{&area} {}

    /**
     * @brief Rebinds a proxy object to a sequence container type.
     * @tparam Type Type of container to wrap.
     * @param instance The container to wrap.
     */
    template<typename Type>
    void rebind(any instance) noexcept {
        value_type_node = &internal::resolve<typename Type::value_type>;
        size_fn = &meta_sequence_container_traits<Type>::size;
        resize_fn = &meta_sequence_container_traits<Type>::resize;
        iter_fn = &meta_sequence_container_traits<Type>::iter;
        insert_or_erase_fn = &meta_sequence_container_traits<Type>::insert_or_erase;
        storage = std::move(instance);
    }

    [[nodiscard]] inline meta_type value_type() const noexcept;
    [[nodiscard]] inline size_type size() const noexcept;
    inline bool resize(const size_type);
    inline bool clear();
    [[nodiscard]] inline iterator begin();
    [[nodiscard]] inline iterator end();
    inline iterator insert(iterator, meta_any);
    inline iterator erase(iterator);
    [[nodiscard]] inline meta_any operator[](const size_type);
    [[nodiscard]] inline explicit operator bool() const noexcept;

private:
    const meta_ctx *ctx{};
    internal::meta_type_node (*value_type_node)(const internal::meta_context &){};
    size_type (*size_fn)(const any &) noexcept {};
    bool (*resize_fn)(any &, size_type){};
    iterator (*iter_fn)(const meta_ctx &, any &, const bool){};
    iterator (*insert_or_erase_fn)(const meta_ctx &, any &, const any &, meta_any &){};
    any storage{};
};

/*! @brief Proxy object for associative containers. */
class meta_associative_container {
    class meta_iterator;

public:
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Meta iterator type. */
    using iterator = meta_iterator;

    /**
     * @brief Context aware constructor.
     * @param area The context from which to search for meta types.
     */
    meta_associative_container(const meta_ctx &area = locator<meta_ctx>::value_or()) noexcept
        : ctx{&area} {}

    /**
     * @brief Rebinds a proxy object to an associative container type.
     * @tparam Type Type of container to wrap.
     * @param instance The container to wrap.
     */
    template<typename Type>
    void rebind(any instance) noexcept {
        if constexpr(!meta_associative_container_traits<Type>::key_only) {
            mapped_type_node = &internal::resolve<typename Type::mapped_type>;
        }

        key_only_container = meta_associative_container_traits<Type>::key_only;
        key_type_node = &internal::resolve<typename Type::key_type>;
        value_type_node = &internal::resolve<typename Type::value_type>;
        size_fn = &meta_associative_container_traits<Type>::size;
        clear_fn = &meta_associative_container_traits<Type>::clear;
        iter_fn = &meta_associative_container_traits<Type>::iter;
        insert_or_erase_fn = &meta_associative_container_traits<Type>::insert_or_erase;
        find_fn = &meta_associative_container_traits<Type>::find;
        storage = std::move(instance);
    }

    [[nodiscard]] inline bool key_only() const noexcept;
    [[nodiscard]] inline meta_type key_type() const noexcept;
    [[nodiscard]] inline meta_type mapped_type() const noexcept;
    [[nodiscard]] inline meta_type value_type() const noexcept;
    [[nodiscard]] inline size_type size() const noexcept;
    inline bool clear();
    [[nodiscard]] inline iterator begin();
    [[nodiscard]] inline iterator end();
    inline bool insert(meta_any);
    inline bool insert(meta_any, meta_any);
    inline size_type erase(meta_any);
    [[nodiscard]] inline iterator find(meta_any);
    [[nodiscard]] inline explicit operator bool() const noexcept;

private:
    const meta_ctx *ctx{};
    bool key_only_container{};
    internal::meta_type_node (*key_type_node)(const internal::meta_context &){};
    internal::meta_type_node (*mapped_type_node)(const internal::meta_context &){};
    internal::meta_type_node (*value_type_node)(const internal::meta_context &){};
    size_type (*size_fn)(const any &) noexcept {};
    bool (*clear_fn)(any &){};
    iterator (*iter_fn)(const meta_ctx &, any &, const bool){};
    size_type (*insert_or_erase_fn)(any &, meta_any &, meta_any &){};
    iterator (*find_fn)(const meta_ctx &, any &, meta_any &){};
    any storage{};
};

/*! @brief Opaque wrapper for values of any type. */
class meta_any {
    enum class operation : std::uint8_t {
        deref,
        seq,
        assoc
    };

    using vtable_type = void(const operation, const any &, void *);

    template<typename Type>
    static void basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const any &value, [[maybe_unused]] void *other) {
        static_assert(std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, Type>, "Invalid type");

        if constexpr(!std::is_void_v<Type>) {
            switch(op) {
            case operation::deref:
                if constexpr(is_meta_pointer_like_v<Type>) {
                    if constexpr(std::is_function_v<typename std::pointer_traits<Type>::element_type>) {
                        static_cast<meta_any *>(other)->emplace<Type>(any_cast<Type>(value));
                    } else if constexpr(!std::is_same_v<std::remove_const_t<typename std::pointer_traits<Type>::element_type>, void>) {
                        using in_place_type = decltype(adl_meta_pointer_like<Type>::dereference(any_cast<const Type &>(value)));

                        if constexpr(std::is_constructible_v<bool, Type>) {
                            if(const auto &pointer_like = any_cast<const Type &>(value); pointer_like) {
                                static_cast<meta_any *>(other)->emplace<in_place_type>(adl_meta_pointer_like<Type>::dereference(pointer_like));
                            }
                        } else {
                            static_cast<meta_any *>(other)->emplace<in_place_type>(adl_meta_pointer_like<Type>::dereference(any_cast<const Type &>(value)));
                        }
                    }
                }
                break;
            case operation::seq:
                if constexpr(is_complete_v<meta_sequence_container_traits<Type>>) {
                    static_cast<meta_sequence_container *>(other)->rebind<Type>(std::move(const_cast<any &>(value)));
                }
                break;
            case operation::assoc:
                if constexpr(is_complete_v<meta_associative_container_traits<Type>>) {
                    static_cast<meta_associative_container *>(other)->rebind<Type>(std::move(const_cast<any &>(value)));
                }
                break;
            }
        }
    }

    void release() {
        if(node.dtor.dtor && owner()) {
            node.dtor.dtor(storage.data());
        }
    }

    meta_any(const meta_ctx &area, const meta_any &other, any ref) noexcept
        : storage{std::move(ref)},
          ctx{&area},
          node{storage ? other.node : internal::meta_type_node{}},
          vtable{storage ? other.vtable : &basic_vtable<void>} {}

public:
    /*! Default constructor. */
    meta_any() noexcept
        : meta_any{meta_ctx_arg, locator<meta_ctx>::value_or()} {}

    /**
     * @brief Context aware constructor.
     * @param area The context from which to search for meta types.
     */
    meta_any(meta_ctx_arg_t, const meta_ctx &area) noexcept
        : storage{},
          ctx{&area},
          node{},
          vtable{&basic_vtable<void>} {}

    /**
     * @brief Constructs a wrapper by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit meta_any(std::in_place_type_t<Type>, Args &&...args)
        : meta_any{locator<meta_ctx>::value_or(), std::in_place_type<Type>, std::forward<Args>(args)...} {}

    /**
     * @brief Constructs a wrapper by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param area The context from which to search for meta types.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit meta_any(const meta_ctx &area, std::in_place_type_t<Type>, Args &&...args)
        : storage{std::in_place_type<Type>, std::forward<Args>(args)...},
          ctx{&area},
          node{internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(internal::meta_context::from(*ctx))},
          vtable{&basic_vtable<std::remove_cv_t<std::remove_reference_t<Type>>>} {}

    /**
     * @brief Constructs a wrapper from a given value.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>>>
    meta_any(Type &&value)
        : meta_any{locator<meta_ctx>::value_or(), std::forward<Type>(value)} {}

    /**
     * @brief Constructs a wrapper from a given value.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param area The context from which to search for meta types.
     * @param value An instance of an object to use to initialize the wrapper.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>>>
    meta_any(const meta_ctx &area, Type &&value)
        : meta_any{area, std::in_place_type<std::decay_t<Type>>, std::forward<Type>(value)} {}

    /**
     * @brief Context aware copy constructor.
     * @param area The context from which to search for meta types.
     * @param other The instance to copy from.
     */
    meta_any(const meta_ctx &area, const meta_any &other)
        : meta_any{other} {
        ctx = &area;
        node = node.resolve ? node.resolve(internal::meta_context::from(*ctx)) : node;
    }

    /**
     * @brief Context aware move constructor.
     * @param area The context from which to search for meta types.
     * @param other The instance to move from.
     */
    meta_any(const meta_ctx &area, meta_any &&other)
        : meta_any{std::move(other)} {
        ctx = &area;
        node = node.resolve ? node.resolve(internal::meta_context::from(*ctx)) : node;
    }

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    meta_any(const meta_any &other) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    meta_any(meta_any &&other) noexcept
        : storage{std::move(other.storage)},
          ctx{other.ctx},
          node{std::exchange(other.node, internal::meta_type_node{})},
          vtable{std::exchange(other.vtable, &basic_vtable<void>)} {}

    /*! @brief Frees the internal storage, whatever it means. */
    ~meta_any() {
        release();
    }

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This meta any object.
     */
    meta_any &operator=(const meta_any &other) {
        release();
        storage = other.storage;
        ctx = other.ctx;
        node = other.node;
        vtable = other.vtable;
        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This meta any object.
     */
    meta_any &operator=(meta_any &&other) noexcept {
        release();
        storage = std::move(other.storage);
        ctx = other.ctx;
        node = std::exchange(other.node, internal::meta_type_node{});
        vtable = std::exchange(other.vtable, &basic_vtable<void>);
        return *this;
    }

    /**
     * @brief Value assignment operator.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     * @return This meta any object.
     */
    template<typename Type>
    std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>, meta_any &>
    operator=(Type &&value) {
        emplace<std::decay_t<Type>>(std::forward<Type>(value));
        return *this;
    }

    /*! @copydoc any::type */
    [[nodiscard]] inline meta_type type() const noexcept;

    /*! @copydoc any::data */
    [[nodiscard]] const void *data() const noexcept {
        return storage.data();
    }

    /*! @copydoc any::data */
    [[nodiscard]] void *data() noexcept {
        return storage.data();
    }

    /**
     * @brief Invokes the underlying function, if possible.
     * @tparam Args Types of arguments to use to invoke the function.
     * @param id Unique identifier.
     * @param args Parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    template<typename... Args>
    meta_any invoke(const id_type id, Args &&...args) const;

    /*! @copydoc invoke */
    template<typename... Args>
    meta_any invoke(const id_type id, Args &&...args);

    /**
     * @brief Sets the value of a given variable.
     * @tparam Type Type of value to assign.
     * @param id Unique identifier.
     * @param value Parameter to use to set the underlying variable.
     * @return True in case of success, false otherwise.
     */
    template<typename Type>
    bool set(const id_type id, Type &&value);

    /**
     * @brief Gets the value of a given variable.
     * @param id Unique identifier.
     * @return A wrapper containing the value of the underlying variable.
     */
    [[nodiscard]] meta_any get(const id_type id) const;

    /*! @copydoc get */
    [[nodiscard]] meta_any get(const id_type id);

    /**
     * @brief Tries to cast an instance to a given type.
     * @tparam Type Type to which to cast the instance.
     * @return A (possibly null) pointer to the contained instance.
     */
    template<typename Type>
    [[nodiscard]] const Type *try_cast() const {
        const auto other = internal::resolve<std::remove_cv_t<Type>>(internal::meta_context::from(*ctx));
        return static_cast<const Type *>(internal::try_cast(internal::meta_context::from(*ctx), node, other, data()));
    }

    /*! @copydoc try_cast */
    template<typename Type>
    [[nodiscard]] Type *try_cast() {
        if constexpr(std::is_const_v<Type>) {
            return std::as_const(*this).try_cast<std::remove_const_t<Type>>();
        } else {
            const auto other = internal::resolve<std::remove_cv_t<Type>>(internal::meta_context::from(*ctx));
            return static_cast<Type *>(const_cast<void *>(internal::try_cast(internal::meta_context::from(*ctx), node, other, data())));
        }
    }

    /**
     * @brief Tries to cast an instance to a given type.
     *
     * @warning
     * Attempting to perform an invalid cast results is undefined behavior.
     *
     * @tparam Type Type to which to cast the instance.
     * @return A reference to the contained instance.
     */
    template<typename Type>
    [[nodiscard]] Type cast() const {
        auto *const instance = try_cast<std::remove_reference_t<Type>>();
        ENTT_ASSERT(instance, "Invalid instance");
        return static_cast<Type>(*instance);
    }

    /*! @copydoc cast */
    template<typename Type>
    [[nodiscard]] Type cast() {
        // forces const on non-reference types to make them work also with wrappers for const references
        auto *const instance = try_cast<std::remove_reference_t<const Type>>();
        ENTT_ASSERT(instance, "Invalid instance");
        return static_cast<Type>(*instance);
    }

    /**
     * @brief Converts an object in such a way that a given cast becomes viable.
     * @param type Meta type to which the cast is requested.
     * @return A valid meta any object if there exists a viable conversion, an
     * invalid one otherwise.
     */
    [[nodiscard]] meta_any allow_cast(const meta_type &type) const;

    /**
     * @brief Converts an object in such a way that a given cast becomes viable.
     * @param type Meta type to which the cast is requested.
     * @return True if there exists a viable conversion, false otherwise.
     */
    [[nodiscard]] bool allow_cast(const meta_type &type) {
        if(auto other = std::as_const(*this).allow_cast(type); other) {
            if(other.owner()) {
                std::swap(*this, other);
            }

            return true;
        }

        return false;
    }

    /**
     * @brief Converts an object in such a way that a given cast becomes viable.
     * @tparam Type Type to which the cast is requested.
     * @return A valid meta any object if there exists a viable conversion, an
     * invalid one otherwise.
     */
    template<typename Type>
    [[nodiscard]] meta_any allow_cast() const {
        if constexpr(std::is_reference_v<Type> && !std::is_const_v<std::remove_reference_t<Type>>) {
            return meta_any{meta_ctx_arg, *ctx};
        } else {
            auto other = internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(internal::meta_context::from(*ctx));
            return allow_cast(meta_type{*ctx, other});
        }
    }

    /**
     * @brief Converts an object in such a way that a given cast becomes viable.
     * @tparam Type Type to which the cast is requested.
     * @return True if there exists a viable conversion, false otherwise.
     */
    template<typename Type>
    bool allow_cast() {
        auto other = internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(internal::meta_context::from(*ctx));
        return allow_cast(meta_type{*ctx, other}) && (!(std::is_reference_v<Type> && !std::is_const_v<std::remove_reference_t<Type>>) || storage.data() != nullptr);
    }

    /*! @copydoc any::emplace */
    template<typename Type, typename... Args>
    void emplace(Args &&...args) {
        release();
        storage.emplace<Type>(std::forward<Args>(args)...);
        node = internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(internal::meta_context::from(*ctx));
        vtable = &basic_vtable<std::remove_cv_t<std::remove_reference_t<Type>>>;
    }

    /*! @copydoc any::assign */
    bool assign(const meta_any &other);

    /*! @copydoc any::assign */
    bool assign(meta_any &&other);

    /*! @copydoc any::reset */
    void reset() {
        release();
        storage.reset();
        node = {};
        vtable = &basic_vtable<void>;
    }

    /**
     * @brief Returns a sequence container proxy.
     * @return A sequence container proxy for the underlying object.
     */
    [[nodiscard]] meta_sequence_container as_sequence_container() noexcept {
        any detached = storage.as_ref();
        meta_sequence_container proxy{*ctx};
        vtable(operation::seq, detached, &proxy);
        return proxy;
    }

    /*! @copydoc as_sequence_container */
    [[nodiscard]] meta_sequence_container as_sequence_container() const noexcept {
        any detached = storage.as_ref();
        meta_sequence_container proxy{*ctx};
        vtable(operation::seq, detached, &proxy);
        return proxy;
    }

    /**
     * @brief Returns an associative container proxy.
     * @return An associative container proxy for the underlying object.
     */
    [[nodiscard]] meta_associative_container as_associative_container() noexcept {
        any detached = storage.as_ref();
        meta_associative_container proxy{*ctx};
        vtable(operation::assoc, detached, &proxy);
        return proxy;
    }

    /*! @copydoc as_associative_container */
    [[nodiscard]] meta_associative_container as_associative_container() const noexcept {
        any detached = storage.as_ref();
        meta_associative_container proxy{*ctx};
        vtable(operation::assoc, detached, &proxy);
        return proxy;
    }

    /**
     * @brief Indirection operator for dereferencing opaque objects.
     * @return A wrapper that shares a reference to an unmanaged object if the
     * wrapped element is dereferenceable, an invalid meta any otherwise.
     */
    [[nodiscard]] meta_any operator*() const noexcept {
        meta_any ret{meta_ctx_arg, *ctx};
        vtable(operation::deref, storage, &ret);
        return ret;
    }

    /**
     * @brief Returns false if a wrapper is invalid, true otherwise.
     * @return False if the wrapper is invalid, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return !(node.info == nullptr);
    }

    /*! @copydoc any::operator== */
    [[nodiscard]] bool operator==(const meta_any &other) const noexcept {
        return (ctx == other.ctx) && ((!node.info && !other.node.info) || (node.info && other.node.info && *node.info == *other.node.info && storage == other.storage));
    }

    /*! @copydoc any::operator!= */
    [[nodiscard]] bool operator!=(const meta_any &other) const noexcept {
        return !(*this == other);
    }

    /*! @copydoc any::as_ref */
    [[nodiscard]] meta_any as_ref() noexcept {
        return meta_any{*ctx, *this, storage.as_ref()};
    }

    /*! @copydoc any::as_ref */
    [[nodiscard]] meta_any as_ref() const noexcept {
        return meta_any{*ctx, *this, storage.as_ref()};
    }

    /*! @copydoc any::owner */
    [[nodiscard]] bool owner() const noexcept {
        return storage.owner();
    }

private:
    any storage;
    const meta_ctx *ctx;
    internal::meta_type_node node;
    vtable_type *vtable;
};

/**
 * @brief Forwards its argument and avoids copies for lvalue references.
 * @tparam Type Type of argument to use to construct the new instance.
 * @param value Parameter to use to construct the instance.
 * @param ctx The context from which to search for meta types.
 * @return A properly initialized and not necessarily owning wrapper.
 */
template<typename Type>
meta_any forward_as_meta(const meta_ctx &ctx, Type &&value) {
    return meta_any{ctx, std::in_place_type<Type &&>, std::forward<Type>(value)};
}

/**
 * @brief Forwards its argument and avoids copies for lvalue references.
 * @tparam Type Type of argument to use to construct the new instance.
 * @param value Parameter to use to construct the instance.
 * @return A properly initialized and not necessarily owning wrapper.
 */
template<typename Type>
meta_any forward_as_meta(Type &&value) {
    return forward_as_meta(locator<meta_ctx>::value_or(), std::forward<Type>(value));
}

/**
 * @brief Opaque pointers to instances of any type.
 *
 * A handle doesn't perform copies and isn't responsible for the contained
 * object. It doesn't prolong the lifetime of the pointed instance.<br/>
 * Handles are used to generate references to actual objects when needed.
 */
struct meta_handle {
    /*! Default constructor. */
    meta_handle() noexcept
        : meta_handle{meta_ctx_arg, locator<meta_ctx>::value_or()} {}

    /**
     * @brief Context aware constructor.
     * @param area The context from which to search for meta types.
     */
    meta_handle(meta_ctx_arg_t, const meta_ctx &area) noexcept
        : any{meta_ctx_arg, area} {}

    /**
     * @brief Creates a handle that points to an unmanaged object.
     * @param value An instance of an object to use to initialize the handle.
     */
    meta_handle(meta_any &value) noexcept
        : any{value.as_ref()} {}

    /**
     * @brief Creates a handle that points to an unmanaged object.
     * @param value An instance of an object to use to initialize the handle.
     */
    meta_handle(const meta_any &value) noexcept
        : any{value.as_ref()} {}

    /**
     * @brief Creates a handle that points to an unmanaged object.
     * @tparam Type Type of object to use to initialize the handle.
     * @param ctx The context from which to search for meta types.
     * @param value An instance of an object to use to initialize the handle.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_handle>>>
    meta_handle(const meta_ctx &ctx, Type &value) noexcept
        : any{ctx, std::in_place_type<Type &>, value} {}

    /**
     * @brief Creates a handle that points to an unmanaged object.
     * @tparam Type Type of object to use to initialize the handle.
     * @param value An instance of an object to use to initialize the handle.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_handle>>>
    meta_handle(Type &value) noexcept
        : meta_handle{locator<meta_ctx>::value_or(), value} {}

    /**
     * @brief Context aware copy constructor.
     * @param area The context from which to search for meta types.
     * @param other The instance to copy from.
     */
    meta_handle(const meta_ctx &area, const meta_handle &other)
        : any{area, other.any} {}

    /**
     * @brief Context aware move constructor.
     * @param area The context from which to search for meta types.
     * @param other The instance to move from.
     */
    meta_handle(const meta_ctx &area, meta_handle &&other)
        : any{area, std::move(other.any)} {}

    /*! @brief Default copy constructor, deleted on purpose. */
    meta_handle(const meta_handle &) = delete;

    /*! @brief Default move constructor. */
    meta_handle(meta_handle &&) = default;

    /**
     * @brief Default copy assignment operator, deleted on purpose.
     * @return This meta handle.
     */
    meta_handle &operator=(const meta_handle &) = delete;

    /**
     * @brief Default move assignment operator.
     * @return This meta handle.
     */
    meta_handle &operator=(meta_handle &&) = default;

    /**
     * @brief Returns false if a handle is invalid, true otherwise.
     * @return False if the handle is invalid, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(any);
    }

    /**
     * @brief Access operator for accessing the contained opaque object.
     * @return A wrapper that shares a reference to an unmanaged object.
     */
    [[nodiscard]] meta_any *operator->() {
        return &any;
    }

    /*! @copydoc operator-> */
    [[nodiscard]] const meta_any *operator->() const {
        return &any;
    }

private:
    meta_any any;
};

/*! @brief Opaque wrapper for properties of any type. */
struct meta_prop {
    /*! @brief Default constructor. */
    meta_prop() noexcept
        : node{},
          ctx{} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_prop(const meta_ctx &area, const internal::meta_prop_node &curr) noexcept
        : node{&curr},
          ctx{&area} {}

    /**
     * @brief Returns the stored value by copy.
     * @return A wrapper containing the value stored with the property.
     */
    [[nodiscard]] meta_any value() const {
        return node->value ? node->type(internal::meta_context::from(*ctx)).from_void(*ctx, nullptr, node->value.get()) : meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @brief Returns true if an object is valid, false otherwise.
     * @return True if the object is valid, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return (node != nullptr);
    }

private:
    const internal::meta_prop_node *node;
    const meta_ctx *ctx;
};

/*! @brief Opaque wrapper for data members. */
struct meta_data {
    /*! @brief Unsigned integer type. */
    using size_type = typename internal::meta_data_node::size_type;

    /*! @brief Default constructor. */
    meta_data() noexcept
        : node{},
          ctx{} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_data(const meta_ctx &area, const internal::meta_data_node &curr) noexcept
        : node{&curr},
          ctx{&area} {}

    /**
     * @brief Returns the number of setters available.
     * @return The number of setters available.
     */
    [[nodiscard]] size_type arity() const noexcept {
        return node->arity;
    }

    /**
     * @brief Indicates whether a data member is constant or not.
     * @return True if the data member is constant, false otherwise.
     */
    [[nodiscard]] bool is_const() const noexcept {
        return static_cast<bool>(node->traits & internal::meta_traits::is_const);
    }

    /**
     * @brief Indicates whether a data member is static or not.
     * @return True if the data member is static, false otherwise.
     */
    [[nodiscard]] bool is_static() const noexcept {
        return static_cast<bool>(node->traits & internal::meta_traits::is_static);
    }

    /*! @copydoc meta_any::type */
    [[nodiscard]] inline meta_type type() const noexcept;

    /**
     * @brief Sets the value of a given variable.
     * @tparam Type Type of value to assign.
     * @param instance An opaque instance of the underlying type.
     * @param value Parameter to use to set the underlying variable.
     * @return True in case of success, false otherwise.
     */
    template<typename Type>
    bool set(meta_handle instance, Type &&value) const {
        return node->set && node->set(meta_handle{*ctx, std::move(instance)}, meta_any{*ctx, std::forward<Type>(value)});
    }

    /**
     * @brief Gets the value of a given variable.
     * @param instance An opaque instance of the underlying type.
     * @return A wrapper containing the value of the underlying variable.
     */
    [[nodiscard]] meta_any get(meta_handle instance) const {
        return node->get(*ctx, meta_handle{*ctx, std::move(instance)});
    }

    /**
     * @brief Returns the type accepted by the i-th setter.
     * @param index Index of the setter of which to return the accepted type.
     * @return The type accepted by the i-th setter.
     */
    [[nodiscard]] inline meta_type arg(const size_type index) const noexcept;

    /**
     * @brief Returns a range to visit registered meta properties.
     * @return An iterable range to visit registered meta properties.
     */
    [[nodiscard]] meta_range<meta_prop, typename decltype(internal::meta_data_node::prop)::const_iterator> prop() const noexcept {
        return {{*ctx, node->prop.cbegin()}, {*ctx, node->prop.cend()}};
    }

    /**
     * @brief Lookup utility for meta properties.
     * @param key The key to use to search for a property.
     * @return The registered meta property for the given key, if any.
     */
    [[nodiscard]] meta_prop prop(const id_type key) const {
        const auto it = node->prop.find(key);
        return it != node->prop.cend() ? meta_prop{*ctx, it->second} : meta_prop{};
    }

    /**
     * @brief Returns true if an object is valid, false otherwise.
     * @return True if the object is valid, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return (node != nullptr);
    }

private:
    const internal::meta_data_node *node;
    const meta_ctx *ctx;
};

/*! @brief Opaque wrapper for member functions. */
struct meta_func {
    /*! @brief Unsigned integer type. */
    using size_type = typename internal::meta_func_node::size_type;

    /*! @brief Default constructor. */
    meta_func() noexcept
        : node{},
          ctx{} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_func(const meta_ctx &area, const internal::meta_func_node &curr) noexcept
        : node{&curr},
          ctx{&area} {}

    /**
     * @brief Returns the number of arguments accepted by a member function.
     * @return The number of arguments accepted by the member function.
     */
    [[nodiscard]] size_type arity() const noexcept {
        return node->arity;
    }

    /**
     * @brief Indicates whether a member function is constant or not.
     * @return True if the member function is constant, false otherwise.
     */
    [[nodiscard]] bool is_const() const noexcept {
        return static_cast<bool>(node->traits & internal::meta_traits::is_const);
    }

    /**
     * @brief Indicates whether a member function is static or not.
     * @return True if the member function is static, false otherwise.
     */
    [[nodiscard]] bool is_static() const noexcept {
        return static_cast<bool>(node->traits & internal::meta_traits::is_static);
    }

    /**
     * @brief Returns the return type of a member function.
     * @return The return type of the member function.
     */
    [[nodiscard]] inline meta_type ret() const noexcept;

    /**
     * @brief Returns the type of the i-th argument of a member function.
     * @param index Index of the argument of which to return the type.
     * @return The type of the i-th argument of a member function.
     */
    [[nodiscard]] inline meta_type arg(const size_type index) const noexcept;

    /**
     * @brief Invokes the underlying function, if possible.
     *
     * @warning
     * The context of the arguments is **not** changed.<br/>
     * It's up to the caller to bind them to the right context(s).
     *
     * @param instance An opaque instance of the underlying type.
     * @param args Parameters to use to invoke the function.
     * @param sz Number of parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    meta_any invoke(meta_handle instance, meta_any *const args, const size_type sz) const {
        return sz == arity() ? node->invoke(*ctx, meta_handle{*ctx, std::move(instance)}, args) : meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @copybrief invoke
     * @tparam Args Types of arguments to use to invoke the function.
     * @param instance An opaque instance of the underlying type.
     * @param args Parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    template<typename... Args>
    meta_any invoke(meta_handle instance, Args &&...args) const {
        meta_any arguments[sizeof...(Args) + 1u]{{*ctx, std::forward<Args>(args)}...};
        return invoke(meta_handle{*ctx, std::move(instance)}, arguments, sizeof...(Args));
    }

    /*! @copydoc meta_data::prop */
    [[nodiscard]] meta_range<meta_prop, typename decltype(internal::meta_func_node::prop)::const_iterator> prop() const noexcept {
        return {{*ctx, node->prop.cbegin()}, {*ctx, node->prop.cend()}};
    }

    /**
     * @brief Lookup utility for meta properties.
     * @param key The key to use to search for a property.
     * @return The registered meta property for the given key, if any.
     */
    [[nodiscard]] meta_prop prop(const id_type key) const {
        const auto it = node->prop.find(key);
        return it != node->prop.cend() ? meta_prop{*ctx, it->second} : meta_prop{};
    }

    /**
     * @brief Returns the next overload of a given function, if any.
     * @return The next overload of the given function, if any.
     */
    [[nodiscard]] meta_func next() const {
        return node->next ? meta_func{*ctx, *node->next} : meta_func{};
    }

    /**
     * @brief Returns true if an object is valid, false otherwise.
     * @return True if the object is valid, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return (node != nullptr);
    }

private:
    const internal::meta_func_node *node;
    const meta_ctx *ctx;
};

/*! @brief Opaque wrapper for types. */
class meta_type {
    template<typename Func>
    [[nodiscard]] auto lookup(meta_any *const args, const typename internal::meta_type_node::size_type sz, [[maybe_unused]] bool constness, Func next) const {
        decltype(next()) candidate = nullptr;
        size_type same{};
        bool ambiguous{};

        for(auto curr = next(); curr; curr = next()) {
            if constexpr(std::is_same_v<std::decay_t<decltype(*curr)>, internal::meta_func_node>) {
                if(constness && !static_cast<bool>(curr->traits & internal::meta_traits::is_const)) {
                    continue;
                }
            }

            if(curr->arity == sz) {
                size_type match{};
                size_type pos{};

                for(; pos < sz && args[pos]; ++pos) {
                    const auto other = curr->arg(*ctx, pos);
                    const auto type = args[pos].type();

                    if(const auto &info = other.info(); info == type.info()) {
                        ++match;
                    } else if(!((type.node.details && (type.node.details->base.contains(info.hash()) || type.node.details->conv.contains(info.hash()))) || (type.node.conversion_helper && other.node.conversion_helper))) {
                        break;
                    }
                }

                if(pos == sz) {
                    if(!candidate || match > same) {
                        candidate = curr;
                        same = match;
                        ambiguous = false;
                    } else if(match == same) {
                        if constexpr(std::is_same_v<std::decay_t<decltype(*curr)>, internal::meta_func_node>) {
                            if(static_cast<bool>(curr->traits & internal::meta_traits::is_const) != static_cast<bool>(candidate->traits & internal::meta_traits::is_const)) {
                                candidate = static_cast<bool>(candidate->traits & internal::meta_traits::is_const) ? curr : candidate;
                                ambiguous = false;
                                continue;
                            }
                        }

                        ambiguous = true;
                    }
                }
            }
        }

        return ambiguous ? nullptr : candidate;
    }

public:
    /*! @brief Unsigned integer type. */
    using size_type = typename internal::meta_type_node::size_type;

    /*! @brief Default constructor. */
    meta_type() noexcept
        : node{},
          ctx{} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_type(const meta_ctx &area, const internal::meta_type_node &curr) noexcept
        : node{curr},
          ctx{&area} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_type(const meta_ctx &area, const internal::meta_base_node &curr) noexcept
        : meta_type{area, curr.type(internal::meta_context::from(area))} {}

    /**
     * @brief Returns the type info object of the underlying type.
     * @return The type info object of the underlying type.
     */
    [[nodiscard]] const type_info &info() const noexcept {
        return *node.info;
    }

    /**
     * @brief Returns the identifier assigned to a type.
     * @return The identifier assigned to the type.
     */
    [[nodiscard]] id_type id() const noexcept {
        return node.id;
    }

    /**
     * @brief Returns the size of the underlying type if known.
     * @return The size of the underlying type if known, 0 otherwise.
     */
    [[nodiscard]] size_type size_of() const noexcept {
        return node.size_of;
    }

    /**
     * @brief Checks whether a type refers to an arithmetic type or not.
     * @return True if the underlying type is an arithmetic type, false
     * otherwise.
     */
    [[nodiscard]] bool is_arithmetic() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_arithmetic);
    }

    /**
     * @brief Checks whether a type refers to an integral type or not.
     * @return True if the underlying type is an integral type, false otherwise.
     */
    [[nodiscard]] bool is_integral() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_integral);
    }

    /**
     * @brief Checks whether a type refers to a signed type or not.
     * @return True if the underlying type is a signed type, false otherwise.
     */
    [[nodiscard]] bool is_signed() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_signed);
    }

    /**
     * @brief Checks whether a type refers to an array type or not.
     * @return True if the underlying type is an array type, false otherwise.
     */
    [[nodiscard]] bool is_array() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_array);
    }

    /**
     * @brief Checks whether a type refers to an enum or not.
     * @return True if the underlying type is an enum, false otherwise.
     */
    [[nodiscard]] bool is_enum() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_enum);
    }

    /**
     * @brief Checks whether a type refers to a class or not.
     * @return True if the underlying type is a class, false otherwise.
     */
    [[nodiscard]] bool is_class() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_class);
    }

    /**
     * @brief Checks whether a type refers to a pointer or not.
     * @return True if the underlying type is a pointer, false otherwise.
     */
    [[nodiscard]] bool is_pointer() const noexcept {
        return node.info && (node.info->hash() != remove_pointer().info().hash());
    }

    /**
     * @brief Provides the type for which the pointer is defined.
     * @return The type for which the pointer is defined or this type if it
     * doesn't refer to a pointer type.
     */
    [[nodiscard]] meta_type remove_pointer() const noexcept {
        return {*ctx, node.remove_pointer(internal::meta_context::from(*ctx))};
    }

    /**
     * @brief Checks whether a type is a pointer-like type or not.
     * @return True if the underlying type is a pointer-like one, false
     * otherwise.
     */
    [[nodiscard]] bool is_pointer_like() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_meta_pointer_like);
    }

    /**
     * @brief Checks whether a type refers to a sequence container or not.
     * @return True if the type is a sequence container, false otherwise.
     */
    [[nodiscard]] bool is_sequence_container() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_meta_sequence_container);
    }

    /**
     * @brief Checks whether a type refers to an associative container or not.
     * @return True if the type is an associative container, false otherwise.
     */
    [[nodiscard]] bool is_associative_container() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_meta_associative_container);
    }

    /**
     * @brief Checks whether a type refers to a recognized class template
     * specialization or not.
     * @return True if the type is a recognized class template specialization,
     * false otherwise.
     */
    [[nodiscard]] bool is_template_specialization() const noexcept {
        return (node.templ.arity != 0u);
    }

    /**
     * @brief Returns the number of template arguments.
     * @return The number of template arguments.
     */
    [[nodiscard]] size_type template_arity() const noexcept {
        return node.templ.arity;
    }

    /**
     * @brief Returns a tag for the class template of the underlying type.
     * @return The tag for the class template of the underlying type.
     */
    [[nodiscard]] inline meta_type template_type() const noexcept {
        return node.templ.type ? meta_type{*ctx, node.templ.type(internal::meta_context::from(*ctx))} : meta_type{};
    }

    /**
     * @brief Returns the type of the i-th template argument of a type.
     * @param index Index of the template argument of which to return the type.
     * @return The type of the i-th template argument of a type.
     */
    [[nodiscard]] inline meta_type template_arg(const size_type index) const noexcept {
        return index < template_arity() ? meta_type{*ctx, node.templ.arg(internal::meta_context::from(*ctx), index)} : meta_type{};
    }

    /**
     * @brief Returns a range to visit registered top-level base meta types.
     * @return An iterable range to visit registered top-level base meta types.
     */
    [[nodiscard]] meta_range<meta_type, typename decltype(internal::meta_type_descriptor::base)::const_iterator> base() const noexcept {
        using range_type = meta_range<meta_type, typename decltype(internal::meta_type_descriptor::base)::const_iterator>;
        return node.details ? range_type{{*ctx, node.details->base.cbegin()}, {*ctx, node.details->base.cend()}} : range_type{};
    }

    /**
     * @brief Returns a range to visit registered top-level meta data.
     * @return An iterable range to visit registered top-level meta data.
     */
    [[nodiscard]] meta_range<meta_data, typename decltype(internal::meta_type_descriptor::data)::const_iterator> data() const noexcept {
        using range_type = meta_range<meta_data, typename decltype(internal::meta_type_descriptor::data)::const_iterator>;
        return node.details ? range_type{{*ctx, node.details->data.cbegin()}, {*ctx, node.details->data.cend()}} : range_type{};
    }

    /**
     * @brief Lookup utility for meta data (bases are also visited).
     * @param id Unique identifier.
     * @return The registered meta data for the given identifier, if any.
     */
    [[nodiscard]] meta_data data(const id_type id) const {
        if(node.details) {
            if(const auto it = node.details->data.find(id); it != node.details->data.cend()) {
                return meta_data{*ctx, it->second};
            }
        }

        for(auto &&curr: base()) {
            if(auto elem = curr.second.data(id); elem) {
                return elem;
            }
        }

        return meta_data{};
    }

    /**
     * @brief Returns a range to visit registered top-level functions.
     * @return An iterable range to visit registered top-level functions.
     */
    [[nodiscard]] meta_range<meta_func, typename decltype(internal::meta_type_descriptor::func)::const_iterator> func() const noexcept {
        using return_type = meta_range<meta_func, typename decltype(internal::meta_type_descriptor::func)::const_iterator>;
        return node.details ? return_type{{*ctx, node.details->func.cbegin()}, {*ctx, node.details->func.cend()}} : return_type{};
    }

    /**
     * @brief Lookup utility for meta functions (bases are also visited).
     *
     * In case of overloaded functions, the first one with the required
     * identifier is returned.
     *
     * @param id Unique identifier.
     * @return The registered meta function for the given identifier, if any.
     */
    [[nodiscard]] meta_func func(const id_type id) const {
        if(node.details) {
            if(const auto it = node.details->func.find(id); it != node.details->func.cend()) {
                return meta_func{*ctx, it->second};
            }
        }

        for(auto &&curr: base()) {
            if(auto elem = curr.second.func(id); elem) {
                return elem;
            }
        }

        return meta_func{};
    }

    /**
     * @brief Creates an instance of the underlying type, if possible.
     *
     * If suitable, the implicitly generated default constructor is used.
     *
     * @warning
     * The context of the arguments is **not** changed.<br/>
     * It's up to the caller to bind them to the right context(s).
     *
     * @param args Parameters to use to construct the instance.
     * @param sz Number of parameters to use to construct the instance.
     * @return A wrapper containing the new instance, if any.
     */
    [[nodiscard]] meta_any construct(meta_any *const args, const size_type sz) const {
        if(node.details) {
            if(const auto *candidate = lookup(args, sz, false, [first = node.details->ctor.cbegin(), last = node.details->ctor.cend()]() mutable { return first == last ? nullptr : &(first++)->second; }); candidate) {
                return candidate->invoke(*ctx, args);
            }
        }

        if(sz == 0u && node.default_constructor) {
            return node.default_constructor(*ctx);
        }

        return meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @copybrief construct
     * @tparam Args Types of arguments to use to construct the instance.
     * @param args Parameters to use to construct the instance.
     * @return A wrapper containing the new instance, if any.
     */
    template<typename... Args>
    [[nodiscard]] meta_any construct(Args &&...args) const {
        meta_any arguments[sizeof...(Args) + 1u]{{*ctx, std::forward<Args>(args)}...};
        return construct(arguments, sizeof...(Args));
    }

    /**
     * @brief Wraps an opaque element of the underlying type.
     * @param element A valid pointer to an element of the underlying type.
     * @return A wrapper that references the given instance.
     */
    meta_any from_void(void *element) const {
        return (element && node.from_void) ? node.from_void(*ctx, element, nullptr) : meta_any{meta_ctx_arg, *ctx};
    }

    /*! @copydoc from_void */
    meta_any from_void(const void *element) const {
        return (element && node.from_void) ? node.from_void(*ctx, nullptr, element) : meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @brief Invokes a function given an identifier, if possible.
     *
     * @warning
     * The context of the arguments is **not** changed.<br/>
     * It's up to the caller to bind them to the right context(s).
     *
     * @param id Unique identifier.
     * @param instance An opaque instance of the underlying type.
     * @param args Parameters to use to invoke the function.
     * @param sz Number of parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    meta_any invoke(const id_type id, meta_handle instance, meta_any *const args, const size_type sz) const {
        if(node.details) {
            if(auto it = node.details->func.find(id); it != node.details->func.cend()) {
                if(const auto *candidate = lookup(args, sz, (instance->data() == nullptr), [curr = &it->second]() mutable { return curr ? std::exchange(curr, curr->next.get()) : nullptr; }); candidate) {
                    return candidate->invoke(*ctx, meta_handle{*ctx, std::move(instance)}, args);
                }
            }
        }

        for(auto &&curr: base()) {
            if(auto elem = curr.second.invoke(id, *instance.operator->(), args, sz); elem) {
                return elem;
            }
        }

        return meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @copybrief invoke
     *
     * @param id Unique identifier.
     * @tparam Args Types of arguments to use to invoke the function.
     * @param instance An opaque instance of the underlying type.
     * @param args Parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    template<typename... Args>
    meta_any invoke(const id_type id, meta_handle instance, Args &&...args) const {
        meta_any arguments[sizeof...(Args) + 1u]{{*ctx, std::forward<Args>(args)}...};
        return invoke(id, meta_handle{*ctx, std::move(instance)}, arguments, sizeof...(Args));
    }

    /**
     * @brief Sets the value of a given variable.
     * @tparam Type Type of value to assign.
     * @param id Unique identifier.
     * @param instance An opaque instance of the underlying type.
     * @param value Parameter to use to set the underlying variable.
     * @return True in case of success, false otherwise.
     */
    template<typename Type>
    bool set(const id_type id, meta_handle instance, Type &&value) const {
        const auto candidate = data(id);
        return candidate && candidate.set(std::move(instance), std::forward<Type>(value));
    }

    /**
     * @brief Gets the value of a given variable.
     * @param id Unique identifier.
     * @param instance An opaque instance of the underlying type.
     * @return A wrapper containing the value of the underlying variable.
     */
    [[nodiscard]] meta_any get(const id_type id, meta_handle instance) const {
        const auto candidate = data(id);
        return candidate ? candidate.get(std::move(instance)) : meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @brief Returns a range to visit registered top-level meta properties.
     * @return An iterable range to visit registered top-level meta properties.
     */
    [[nodiscard]] meta_range<meta_prop, typename decltype(internal::meta_type_descriptor::prop)::const_iterator> prop() const noexcept {
        using range_type = meta_range<meta_prop, typename decltype(internal::meta_type_descriptor::prop)::const_iterator>;
        return node.details ? range_type{{*ctx, node.details->prop.cbegin()}, {*ctx, node.details->prop.cend()}} : range_type{};
    }

    /**
     * @brief Lookup utility for meta properties (bases are also visited).
     * @param key The key to use to search for a property.
     * @return The registered meta property for the given key, if any.
     */
    [[nodiscard]] meta_prop prop(const id_type key) const {
        if(node.details) {
            if(const auto it = node.details->prop.find(key); it != node.details->prop.cend()) {
                return meta_prop{*ctx, it->second};
            }
        }

        for(auto &&curr: base()) {
            if(auto elem = curr.second.prop(key); elem) {
                return elem;
            }
        }

        return meta_prop{};
    }

    /**
     * @brief Returns true if an object is valid, false otherwise.
     * @return True if the object is valid, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return !(ctx == nullptr);
    }

    /**
     * @brief Checks if two objects refer to the same type.
     * @param other The object with which to compare.
     * @return True if the objects refer to the same type, false otherwise.
     */
    [[nodiscard]] bool operator==(const meta_type &other) const noexcept {
        return (ctx == other.ctx) && ((!node.info && !other.node.info) || (node.info && other.node.info && *node.info == *other.node.info));
    }

private:
    internal::meta_type_node node;
    const meta_ctx *ctx;
};

/**
 * @brief Checks if two objects refer to the same type.
 * @param lhs An object, either valid or not.
 * @param rhs An object, either valid or not.
 * @return False if the objects refer to the same node, true otherwise.
 */
[[nodiscard]] inline bool operator!=(const meta_type &lhs, const meta_type &rhs) noexcept {
    return !(lhs == rhs);
}

[[nodiscard]] inline meta_type meta_any::type() const noexcept {
    return node.info ? meta_type{*ctx, node} : meta_type{};
}

template<typename... Args>
meta_any meta_any::invoke(const id_type id, Args &&...args) const {
    return type().invoke(id, *this, std::forward<Args>(args)...);
}

template<typename... Args>
meta_any meta_any::invoke(const id_type id, Args &&...args) {
    return type().invoke(id, *this, std::forward<Args>(args)...);
}

template<typename Type>
bool meta_any::set(const id_type id, Type &&value) {
    return type().set(id, *this, std::forward<Type>(value));
}

[[nodiscard]] inline meta_any meta_any::get(const id_type id) const {
    return type().get(id, *this);
}

[[nodiscard]] inline meta_any meta_any::get(const id_type id) {
    return type().get(id, *this);
}

[[nodiscard]] inline meta_any meta_any::allow_cast(const meta_type &type) const {
    if(node.info && *node.info == type.info()) {
        return as_ref();
    }

    if(const auto *value = data(); node.details) {
        if(auto it = node.details->conv.find(type.info().hash()); it != node.details->conv.cend()) {
            return it->second.conv(*ctx, data());
        }

        for(auto &&curr: node.details->base) {
            const auto &as_const = curr.second.type(internal::meta_context::from(*ctx)).from_void(*ctx, nullptr, curr.second.cast(value));

            if(auto other = as_const.allow_cast(type); other) {
                return other;
            }
        }
    }

    if(node.conversion_helper && (type.is_arithmetic() || type.is_enum())) {
        // exploits the fact that arithmetic types and enums are also default constructible
        auto other = type.construct();
        ENTT_ASSERT(other.node.conversion_helper, "Conversion helper not found");
        const auto value = node.conversion_helper(nullptr, storage.data());
        other.node.conversion_helper(other.storage.data(), &value);
        return other;
    }

    return meta_any{meta_ctx_arg, *ctx};
}

inline bool meta_any::assign(const meta_any &other) {
    auto value = other.allow_cast({*ctx, node});
    return value && storage.assign(std::move(value.storage));
}

inline bool meta_any::assign(meta_any &&other) {
    if(*node.info == *other.node.info) {
        return storage.assign(std::move(other.storage));
    }

    return assign(std::as_const(other));
}

[[nodiscard]] inline meta_type meta_data::type() const noexcept {
    return meta_type{*ctx, node->type(internal::meta_context::from(*ctx))};
}

[[nodiscard]] inline meta_type meta_data::arg(const size_type index) const noexcept {
    return index < arity() ? node->arg(*ctx, index) : meta_type{};
}

[[nodiscard]] inline meta_type meta_func::ret() const noexcept {
    return meta_type{*ctx, node->ret(internal::meta_context::from(*ctx))};
}

[[nodiscard]] inline meta_type meta_func::arg(const size_type index) const noexcept {
    return index < arity() ? node->arg(*ctx, index) : meta_type{};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

class meta_sequence_container::meta_iterator final {
    friend class meta_sequence_container;

    enum class operation : std::uint8_t {
        incr,
        deref
    };

    using vtable_type = void(const operation, const any &, const std::ptrdiff_t, meta_any *);

    template<typename It>
    static void basic_vtable(const operation op, const any &value, const std::ptrdiff_t offset, meta_any *other) {
        switch(op) {
        case operation::incr: {
            auto &it = any_cast<It &>(const_cast<any &>(value));
            it = std::next(it, offset);
        } break;
        case operation::deref: {
            const auto &it = any_cast<const It &>(value);
            other->emplace<decltype(*it)>(*it);
        } break;
        }
    }

public:
    using difference_type = std::ptrdiff_t;
    using value_type = meta_any;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    constexpr meta_iterator() noexcept
        : ctx{},
          vtable{},
          handle{} {}

    template<typename It>
    explicit meta_iterator(const meta_ctx &area, It iter) noexcept
        : ctx{&area},
          vtable{&basic_vtable<It>},
          handle{std::move(iter)} {}

    meta_iterator &operator++() noexcept {
        vtable(operation::incr, handle, 1, nullptr);
        return *this;
    }

    meta_iterator operator++(int value) noexcept {
        meta_iterator orig = *this;
        vtable(operation::incr, handle, ++value, nullptr);
        return orig;
    }

    meta_iterator &operator--() noexcept {
        vtable(operation::incr, handle, -1, nullptr);
        return *this;
    }

    meta_iterator operator--(int value) noexcept {
        meta_iterator orig = *this;
        vtable(operation::incr, handle, --value, nullptr);
        return orig;
    }

    [[nodiscard]] reference operator*() const {
        reference other{meta_ctx_arg, *ctx};
        vtable(operation::deref, handle, 0, &other);
        return other;
    }

    [[nodiscard]] pointer operator->() const {
        return operator*();
    }

    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(handle);
    }

    [[nodiscard]] bool operator==(const meta_iterator &other) const noexcept {
        return handle == other.handle;
    }

    [[nodiscard]] bool operator!=(const meta_iterator &other) const noexcept {
        return !(*this == other);
    }

private:
    const meta_ctx *ctx;
    vtable_type *vtable;
    any handle;
};

class meta_associative_container::meta_iterator final {
    enum class operation : std::uint8_t {
        incr,
        deref
    };

    using vtable_type = void(const operation, const any &, std::pair<meta_any, meta_any> *);

    template<bool KeyOnly, typename It>
    static void basic_vtable(const operation op, const any &value, std::pair<meta_any, meta_any> *other) {
        switch(op) {
        case operation::incr:
            ++any_cast<It &>(const_cast<any &>(value));
            break;
        case operation::deref:
            const auto &it = any_cast<const It &>(value);
            if constexpr(KeyOnly) {
                other->first.emplace<decltype(*it)>(*it);
            } else {
                other->first.emplace<decltype((it->first))>(it->first);
                other->second.emplace<decltype((it->second))>(it->second);
            }
            break;
        }
    }

public:
    using difference_type = std::ptrdiff_t;
    using value_type = std::pair<meta_any, meta_any>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    constexpr meta_iterator() noexcept
        : ctx{},
          vtable{},
          handle{} {}

    template<bool KeyOnly, typename It>
    meta_iterator(const meta_ctx &area, std::integral_constant<bool, KeyOnly>, It iter) noexcept
        : ctx{&area},
          vtable{&basic_vtable<KeyOnly, It>},
          handle{std::move(iter)} {}

    meta_iterator &operator++() noexcept {
        vtable(operation::incr, handle, nullptr);
        return *this;
    }

    meta_iterator operator++(int) noexcept {
        meta_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] reference operator*() const {
        reference other{{meta_ctx_arg, *ctx}, {meta_ctx_arg, *ctx}};
        vtable(operation::deref, handle, &other);
        return other;
    }

    [[nodiscard]] pointer operator->() const {
        return operator*();
    }

    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(handle);
    }

    [[nodiscard]] bool operator==(const meta_iterator &other) const noexcept {
        return handle == other.handle;
    }

    [[nodiscard]] bool operator!=(const meta_iterator &other) const noexcept {
        return !(*this == other);
    }

private:
    const meta_ctx *ctx;
    vtable_type *vtable;
    any handle;
};

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Returns the meta value type of a container.
 * @return The meta value type of the container.
 */
[[nodiscard]] inline meta_type meta_sequence_container::value_type() const noexcept {
    return value_type_node ? meta_type{*ctx, value_type_node(internal::meta_context::from(*ctx))} : meta_type{};
}

/**
 * @brief Returns the size of a container.
 * @return The size of the container.
 */
[[nodiscard]] inline meta_sequence_container::size_type meta_sequence_container::size() const noexcept {
    return size_fn(storage);
}

/**
 * @brief Resizes a container to contain a given number of elements.
 * @param sz The new size of the container.
 * @return True in case of success, false otherwise.
 */
inline bool meta_sequence_container::resize(const size_type sz) {
    return resize_fn(storage, sz);
}

/**
 * @brief Clears the content of a container.
 * @return True in case of success, false otherwise.
 */
inline bool meta_sequence_container::clear() {
    return resize_fn(storage, 0u);
}

/**
 * @brief Returns an iterator to the first element of a container.
 * @return An iterator to the first element of the container.
 */
[[nodiscard]] inline meta_sequence_container::iterator meta_sequence_container::begin() {
    return iter_fn(*ctx, storage, false);
}

/**
 * @brief Returns an iterator that is past the last element of a container.
 * @return An iterator that is past the last element of the container.
 */
[[nodiscard]] inline meta_sequence_container::iterator meta_sequence_container::end() {
    return iter_fn(*ctx, storage, true);
}

/**
 * @brief Inserts an element at a specified location of a container.
 * @param it Iterator before which the element will be inserted.
 * @param value Element value to insert.
 * @return A possibly invalid iterator to the inserted element.
 */
inline meta_sequence_container::iterator meta_sequence_container::insert(iterator it, meta_any value) {
    return insert_or_erase_fn(*ctx, storage, it.handle, value);
}

/**
 * @brief Removes a given element from a container.
 * @param it Iterator to the element to remove.
 * @return A possibly invalid iterator following the last removed element.
 */
inline meta_sequence_container::iterator meta_sequence_container::erase(iterator it) {
    return insert(std::move(it), {});
}

/**
 * @brief Returns a reference to the element at a given location of a container
 * (no bounds checking is performed).
 * @param pos The position of the element to return.
 * @return A reference to the requested element properly wrapped.
 */
[[nodiscard]] inline meta_any meta_sequence_container::operator[](const size_type pos) {
    auto it = begin();
    it.operator++(static_cast<int>(pos) - 1);
    return *it;
}

/**
 * @brief Returns false if a proxy is invalid, true otherwise.
 * @return False if the proxy is invalid, true otherwise.
 */
[[nodiscard]] inline meta_sequence_container::operator bool() const noexcept {
    return static_cast<bool>(storage);
}

/**
 * @brief Returns true if a container is also key-only, false otherwise.
 * @return True if the associative container is also key-only, false otherwise.
 */
[[nodiscard]] inline bool meta_associative_container::key_only() const noexcept {
    return key_only_container;
}

/**
 * @brief Returns the meta key type of a container.
 * @return The meta key type of the a container.
 */
[[nodiscard]] inline meta_type meta_associative_container::key_type() const noexcept {
    return key_type_node ? meta_type{*ctx, key_type_node(internal::meta_context::from(*ctx))} : meta_type{};
}

/**
 * @brief Returns the meta mapped type of a container.
 * @return The meta mapped type of the a container.
 */
[[nodiscard]] inline meta_type meta_associative_container::mapped_type() const noexcept {
    return mapped_type_node ? meta_type{*ctx, mapped_type_node(internal::meta_context::from(*ctx))} : meta_type{};
}

/*! @copydoc meta_sequence_container::value_type */
[[nodiscard]] inline meta_type meta_associative_container::value_type() const noexcept {
    return value_type_node ? meta_type{*ctx, value_type_node(internal::meta_context::from(*ctx))} : meta_type{};
}

/*! @copydoc meta_sequence_container::size */
[[nodiscard]] inline meta_associative_container::size_type meta_associative_container::size() const noexcept {
    return size_fn(storage);
}

/*! @copydoc meta_sequence_container::clear */
inline bool meta_associative_container::clear() {
    return clear_fn(storage);
}

/*! @copydoc meta_sequence_container::begin */
[[nodiscard]] inline meta_associative_container::iterator meta_associative_container::begin() {
    return iter_fn(*ctx, storage, false);
}

/*! @copydoc meta_sequence_container::end */
[[nodiscard]] inline meta_associative_container::iterator meta_associative_container::end() {
    return iter_fn(*ctx, storage, true);
}

/**
 * @brief Inserts a key only element into a container.
 * @param key The key of the element to insert.
 * @return A bool denoting whether the insertion took place.
 */
inline bool meta_associative_container::insert(meta_any key) {
    meta_any value{*ctx, std::in_place_type<void>};
    return (insert_or_erase_fn(storage, key, value) != 0u);
}

/**
 * @brief Inserts a key/value element into a container.
 * @param key The key of the element to insert.
 * @param value The value of the element to insert.
 * @return A bool denoting whether the insertion took place.
 */
inline bool meta_associative_container::insert(meta_any key, meta_any value) {
    return (insert_or_erase_fn(storage, key, value) != 0u);
}

/**
 * @brief Removes the specified element from a container.
 * @param key The key of the element to remove.
 * @return A bool denoting whether the removal took place.
 */
inline meta_associative_container::size_type meta_associative_container::erase(meta_any key) {
    return insert(std::move(key), meta_any{meta_ctx_arg, *ctx});
}

/**
 * @brief Returns an iterator to the element with a given key, if any.
 * @param key The key of the element to search.
 * @return An iterator to the element with the given key, if any.
 */
[[nodiscard]] inline meta_associative_container::iterator meta_associative_container::find(meta_any key) {
    return find_fn(*ctx, storage, key);
}

/**
 * @brief Returns false if a proxy is invalid, true otherwise.
 * @return False if the proxy is invalid, true otherwise.
 */
[[nodiscard]] inline meta_associative_container::operator bool() const noexcept {
    return static_cast<bool>(storage);
}

} // namespace entt

#endif

// #include "type_traits.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct is_dynamic_sequence_container: std::false_type {};

template<typename Type>
struct is_dynamic_sequence_container<Type, std::void_t<decltype(&Type::clear)>>: std::true_type {};

template<typename, typename = void>
struct is_key_only_meta_associative_container: std::true_type {};

template<typename Type>
struct is_key_only_meta_associative_container<Type, std::void_t<typename Type::mapped_type>>: std::false_type {};

template<typename Type>
struct basic_meta_sequence_container_traits {
    using iterator = meta_sequence_container::iterator;
    using size_type = std::size_t;

    [[nodiscard]] static size_type size(const any &container) noexcept {
        return any_cast<const Type &>(container).size();
    }

    [[nodiscard]] static bool resize([[maybe_unused]] any &container, [[maybe_unused]] size_type sz) {
        if constexpr(is_dynamic_sequence_container<Type>::value) {
            if(auto *const cont = any_cast<Type>(&container); cont) {
                cont->resize(sz);
                return true;
            }
        }

        return false;
    }

    [[nodiscard]] static iterator iter(const meta_ctx &ctx, any &container, const bool as_end) {
        if(auto *const cont = any_cast<Type>(&container); cont) {
            return iterator{ctx, as_end ? cont->end() : cont->begin()};
        }

        const Type &as_const = any_cast<const Type &>(container);
        return iterator{ctx, as_end ? as_const.end() : as_const.begin()};
    }

    [[nodiscard]] static iterator insert_or_erase([[maybe_unused]] const meta_ctx &ctx, [[maybe_unused]] any &container, [[maybe_unused]] const any &handle, [[maybe_unused]] meta_any &value) {
        if constexpr(is_dynamic_sequence_container<Type>::value) {
            if(auto *const cont = any_cast<Type>(&container); cont) {
                typename Type::const_iterator it{};

                if(auto *non_const = any_cast<typename Type::iterator>(&handle); non_const) {
                    it = *non_const;
                } else {
                    it = any_cast<const typename Type::const_iterator &>(handle);
                }

                if(value) {
                    // this abomination is necessary because only on macos value_type and const_reference are different types for std::vector<bool>
                    if(value.allow_cast<typename Type::const_reference>() || value.allow_cast<typename Type::value_type>()) {
                        const auto *element = value.try_cast<std::remove_reference_t<typename Type::const_reference>>();
                        return iterator{ctx, cont->insert(it, element ? *element : value.cast<typename Type::value_type>())};
                    }
                } else {
                    return iterator{ctx, cont->erase(it)};
                }
            }
        }

        return iterator{};
    }
};

template<typename Type>
struct basic_meta_associative_container_traits {
    using iterator = meta_associative_container::iterator;
    using size_type = std::size_t;

    static constexpr auto key_only = is_key_only_meta_associative_container<Type>::value;

    [[nodiscard]] static size_type size(const any &container) noexcept {
        return any_cast<const Type &>(container).size();
    }

    [[nodiscard]] static bool clear(any &container) {
        if(auto *const cont = any_cast<Type>(&container); cont) {
            cont->clear();
            return true;
        }

        return false;
    }

    [[nodiscard]] static iterator iter(const meta_ctx &ctx, any &container, const bool as_end) {
        if(auto *const cont = any_cast<Type>(&container); cont) {
            return iterator{ctx, std::bool_constant<key_only>{}, as_end ? cont->end() : cont->begin()};
        }

        const auto &as_const = any_cast<const Type &>(container);
        return iterator{ctx, std::bool_constant<key_only>{}, as_end ? as_const.end() : as_const.begin()};
    }

    [[nodiscard]] static size_type insert_or_erase(any &container, meta_any &key, meta_any &value) {
        if(auto *const cont = any_cast<Type>(&container); cont && key.allow_cast<const typename Type::key_type &>()) {
            if(value) {
                if constexpr(key_only) {
                    return cont->insert(key.cast<const typename Type::key_type &>()).second;
                } else {
                    return value.allow_cast<const typename Type::mapped_type &>() && cont->emplace(key.cast<const typename Type::key_type &>(), value.cast<const typename Type::mapped_type &>()).second;
                }
            } else {
                return cont->erase(key.cast<const typename Type::key_type &>());
            }
        }

        return 0u;
    }

    [[nodiscard]] static iterator find(const meta_ctx &ctx, any &container, meta_any &key) {
        if(key.allow_cast<const typename Type::key_type &>()) {
            if(auto *const cont = any_cast<Type>(&container); cont) {
                return iterator{ctx, std::bool_constant<key_only>{}, cont->find(key.cast<const typename Type::key_type &>())};
            }

            return iterator{ctx, std::bool_constant<key_only>{}, any_cast<const Type &>(container).find(key.cast<const typename Type::key_type &>())};
        }

        return iterator{};
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Meta sequence container traits for `std::vector`s of any type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_sequence_container_traits<std::vector<Args...>>
    : internal::basic_meta_sequence_container_traits<std::vector<Args...>> {};

/**
 * @brief Meta sequence container traits for `std::array`s of any type.
 * @tparam Type Template arguments for the container.
 * @tparam N Template arguments for the container.
 */
template<typename Type, auto N>
struct meta_sequence_container_traits<std::array<Type, N>>
    : internal::basic_meta_sequence_container_traits<std::array<Type, N>> {};

/**
 * @brief Meta sequence container traits for `std::list`s of any type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_sequence_container_traits<std::list<Args...>>
    : internal::basic_meta_sequence_container_traits<std::list<Args...>> {};

/**
 * @brief Meta sequence container traits for `std::deque`s of any type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_sequence_container_traits<std::deque<Args...>>
    : internal::basic_meta_sequence_container_traits<std::deque<Args...>> {};

/**
 * @brief Meta associative container traits for `std::map`s of any type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_associative_container_traits<std::map<Args...>>
    : internal::basic_meta_associative_container_traits<std::map<Args...>> {};

/**
 * @brief Meta associative container traits for `std::unordered_map`s of any
 * type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_associative_container_traits<std::unordered_map<Args...>>
    : internal::basic_meta_associative_container_traits<std::unordered_map<Args...>> {};

/**
 * @brief Meta associative container traits for `std::set`s of any type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_associative_container_traits<std::set<Args...>>
    : internal::basic_meta_associative_container_traits<std::set<Args...>> {};

/**
 * @brief Meta associative container traits for `std::unordered_set`s of any
 * type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_associative_container_traits<std::unordered_set<Args...>>
    : internal::basic_meta_associative_container_traits<std::unordered_set<Args...>> {};

/**
 * @brief Meta associative container traits for `dense_map`s of any type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_associative_container_traits<dense_map<Args...>>
    : internal::basic_meta_associative_container_traits<dense_map<Args...>> {};

/**
 * @brief Meta associative container traits for `dense_set`s of any type.
 * @tparam Args Template arguments for the container.
 */
template<typename... Args>
struct meta_associative_container_traits<dense_set<Args...>>
    : internal::basic_meta_associative_container_traits<dense_set<Args...>> {};

} // namespace entt

#endif

// #include "meta/context.hpp"
#ifndef ENTT_META_CTX_HPP
#define ENTT_META_CTX_HPP

// #include "../container/dense_map.hpp"

// #include "../core/fwd.hpp"

// #include "../core/utility.hpp"


namespace entt {

class meta_ctx;

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct meta_type_node;

struct meta_context {
    dense_map<id_type, meta_type_node, identity> value{};

    static inline meta_context &from(meta_ctx &ctx);
    static inline const meta_context &from(const meta_ctx &ctx);
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @brief Disambiguation tag for constructors and the like. */
class meta_ctx_arg_t final {};

/*! @brief Constant of type meta_context_arg_t used to disambiguate calls. */
inline constexpr meta_ctx_arg_t meta_ctx_arg{};

/*! @brief Opaque meta context type. */
class meta_ctx: private internal::meta_context {
    /*! @brief Attorney idiom like model to access the base class. */
    friend struct internal::meta_context;
};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

inline internal::meta_context &internal::meta_context::from(meta_ctx &ctx) {
    return ctx;
}

inline const internal::meta_context &internal::meta_context::from(const meta_ctx &ctx) {
    return ctx;
}

/**
 * Internal details not to be documented.
 * @endcond
 */

} // namespace entt

#endif

// #include "meta/factory.hpp"
#ifndef ENTT_META_FACTORY_HPP
#define ENTT_META_FACTORY_HPP

#include <cstddef>
#include <functional>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/fwd.hpp"

// #include "../core/type_info.hpp"

// #include "../core/type_traits.hpp"

// #include "../locator/locator.hpp"

// #include "context.hpp"

// #include "meta.hpp"

// #include "node.hpp"

// #include "policy.hpp"
#ifndef ENTT_META_POLICY_HPP
#define ENTT_META_POLICY_HPP

#include <type_traits>

namespace entt {

/*! @brief Empty class type used to request the _as ref_ policy. */
struct as_ref_t final {
    /**
     * @cond TURN_OFF_DOXYGEN
     * Internal details not to be documented.
     */
    template<typename Type>
    static constexpr bool value = std::is_reference_v<Type> && !std::is_const_v<std::remove_reference_t<Type>>;
    /**
     * Internal details not to be documented.
     * @endcond
     */
};

/*! @brief Empty class type used to request the _as cref_ policy. */
struct as_cref_t final {
    /**
     * @cond TURN_OFF_DOXYGEN
     * Internal details not to be documented.
     */
    template<typename Type>
    static constexpr bool value = std::is_reference_v<Type>;
    /**
     * Internal details not to be documented.
     * @endcond
     */
};

/*! @brief Empty class type used to request the _as-is_ policy. */
struct as_is_t final {
    /**
     * @cond TURN_OFF_DOXYGEN
     * Internal details not to be documented.
     */
    template<typename>
    static constexpr bool value = true;
    /**
     * Internal details not to be documented.
     * @endcond
     */
};

/*! @brief Empty class type used to request the _as void_ policy. */
struct as_void_t final {
    /**
     * @cond TURN_OFF_DOXYGEN
     * Internal details not to be documented.
     */
    template<typename>
    static constexpr bool value = true;
    /**
     * Internal details not to be documented.
     * @endcond
     */
};

/**
 * @brief Provides the member constant `value` to true if a type also is a meta
 * policy, false otherwise.
 * @tparam Type Type to check.
 */
template<typename Type>
struct is_meta_policy
    : std::disjunction<
          std::is_same<Type, as_ref_t>,
          std::is_same<Type, as_cref_t>,
          std::is_same<Type, as_is_t>,
          std::is_same<Type, as_void_t>> {};

/**
 * @brief Helper variable template.
 * @tparam Type Type to check.
 */
template<typename Type>
inline constexpr bool is_meta_policy_v = is_meta_policy<Type>::value;

} // namespace entt

#endif

// #include "range.hpp"

// #include "resolve.hpp"
#ifndef ENTT_META_RESOLVE_HPP
#define ENTT_META_RESOLVE_HPP

#include <type_traits>
// #include "../core/type_info.hpp"

// #include "../locator/locator.hpp"

// #include "context.hpp"

// #include "meta.hpp"

// #include "node.hpp"

// #include "range.hpp"


namespace entt {

/**
 * @brief Returns the meta type associated with a given type.
 * @tparam Type Type to use to search for a meta type.
 * @param ctx The context from which to search for meta types.
 * @return The meta type associated with the given type, if any.
 */
template<typename Type>
[[nodiscard]] meta_type resolve(const meta_ctx &ctx) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    return {ctx, internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(context)};
}

/**
 * @brief Returns the meta type associated with a given type.
 * @tparam Type Type to use to search for a meta type.
 * @return The meta type associated with the given type, if any.
 */
template<typename Type>
[[nodiscard]] meta_type resolve() noexcept {
    return resolve<Type>(locator<meta_ctx>::value_or());
}

/**
 * @brief Returns a range to use to visit all meta types.
 * @param ctx The context from which to search for meta types.
 * @return An iterable range to use to visit all meta types.
 */
[[nodiscard]] inline meta_range<meta_type, typename decltype(internal::meta_context::value)::const_iterator> resolve(const meta_ctx &ctx) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    return {{ctx, context.value.cbegin()}, {ctx, context.value.cend()}};
}

/**
 * @brief Returns a range to use to visit all meta types.
 * @return An iterable range to use to visit all meta types.
 */
[[nodiscard]] inline meta_range<meta_type, typename decltype(internal::meta_context::value)::const_iterator> resolve() noexcept {
    return resolve(locator<meta_ctx>::value_or());
}

/**
 * @brief Returns the meta type associated with a given identifier, if any.
 * @param ctx The context from which to search for meta types.
 * @param id Unique identifier.
 * @return The meta type associated with the given identifier, if any.
 */
[[nodiscard]] inline meta_type resolve(const meta_ctx &ctx, const id_type id) noexcept {
    for(auto &&curr: resolve(ctx)) {
        if(curr.second.id() == id) {
            return curr.second;
        }
    }

    return meta_type{};
}

/**
 * @brief Returns the meta type associated with a given identifier, if any.
 * @param id Unique identifier.
 * @return The meta type associated with the given identifier, if any.
 */
[[nodiscard]] inline meta_type resolve(const id_type id) noexcept {
    return resolve(locator<meta_ctx>::value_or(), id);
}

/**
 * @brief Returns the meta type associated with a given type info object.
 * @param ctx The context from which to search for meta types.
 * @param info The type info object of the requested type.
 * @return The meta type associated with the given type info object, if any.
 */
[[nodiscard]] inline meta_type resolve(const meta_ctx &ctx, const type_info &info) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    const auto *elem = internal::try_resolve(context, info);
    return elem ? meta_type{ctx, *elem} : meta_type{};
}

/**
 * @brief Returns the meta type associated with a given type info object.
 * @param info The type info object of the requested type.
 * @return The meta type associated with the given type info object, if any.
 */
[[nodiscard]] inline meta_type resolve(const type_info &info) noexcept {
    return resolve(locator<meta_ctx>::value_or(), info);
}

} // namespace entt

#endif

// #include "utility.hpp"
#ifndef ENTT_META_UTILITY_HPP
#define ENTT_META_UTILITY_HPP

#include <cstddef>
#include <functional>
#include <type_traits>
#include <utility>
// #include "../core/type_traits.hpp"

// #include "../locator/locator.hpp"

// #include "meta.hpp"

// #include "node.hpp"

// #include "policy.hpp"


namespace entt {

/**
 * @brief Meta function descriptor traits.
 * @tparam Ret Function return type.
 * @tparam Args Function arguments.
 * @tparam Static Function staticness.
 * @tparam Const Function constness.
 */
template<typename Ret, typename Args, bool Static, bool Const>
struct meta_function_descriptor_traits {
    /*! @brief Meta function return type. */
    using return_type = Ret;
    /*! @brief Meta function arguments. */
    using args_type = Args;

    /*! @brief True if the meta function is static, false otherwise. */
    static constexpr bool is_static = Static;
    /*! @brief True if the meta function is const, false otherwise. */
    static constexpr bool is_const = Const;
};

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct meta_function_descriptor;

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Ret Function return type.
 * @tparam Class Actual owner of the member function.
 * @tparam Args Function arguments.
 */
template<typename Type, typename Ret, typename Class, typename... Args>
struct meta_function_descriptor<Type, Ret (Class::*)(Args...) const>
    : meta_function_descriptor_traits<
          Ret,
          std::conditional_t<std::is_base_of_v<Class, Type>, type_list<Args...>, type_list<const Class &, Args...>>,
          !std::is_base_of_v<Class, Type>,
          true> {};

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Ret Function return type.
 * @tparam Class Actual owner of the member function.
 * @tparam Args Function arguments.
 */
template<typename Type, typename Ret, typename Class, typename... Args>
struct meta_function_descriptor<Type, Ret (Class::*)(Args...)>
    : meta_function_descriptor_traits<
          Ret,
          std::conditional_t<std::is_base_of_v<Class, Type>, type_list<Args...>, type_list<Class &, Args...>>,
          !std::is_base_of_v<Class, Type>,
          false> {};

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta data is associated.
 * @tparam Class Actual owner of the data member.
 * @tparam Ret Data member type.
 */
template<typename Type, typename Ret, typename Class>
struct meta_function_descriptor<Type, Ret Class::*>
    : meta_function_descriptor_traits<
          Ret &,
          std::conditional_t<std::is_base_of_v<Class, Type>, type_list<>, type_list<Class &>>,
          !std::is_base_of_v<Class, Type>,
          false> {};

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Ret Function return type.
 * @tparam MaybeType First function argument.
 * @tparam Args Other function arguments.
 */
template<typename Type, typename Ret, typename MaybeType, typename... Args>
struct meta_function_descriptor<Type, Ret (*)(MaybeType, Args...)>
    : meta_function_descriptor_traits<
          Ret,
          std::conditional_t<std::is_base_of_v<std::remove_cv_t<std::remove_reference_t<MaybeType>>, Type>, type_list<Args...>, type_list<MaybeType, Args...>>,
          !std::is_base_of_v<std::remove_cv_t<std::remove_reference_t<MaybeType>>, Type>,
          std::is_base_of_v<std::remove_cv_t<std::remove_reference_t<MaybeType>>, Type> && std::is_const_v<std::remove_reference_t<MaybeType>>> {};

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Ret Function return type.
 */
template<typename Type, typename Ret>
struct meta_function_descriptor<Type, Ret (*)()>
    : meta_function_descriptor_traits<
          Ret,
          type_list<>,
          true,
          false> {};

/**
 * @brief Meta function helper.
 *
 * Converts a function type to be associated with a reflected type into its meta
 * function descriptor.
 *
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Candidate The actual function to associate with the reflected type.
 */
template<typename Type, typename Candidate>
class meta_function_helper {
    template<typename Ret, typename... Args, typename Class>
    static constexpr meta_function_descriptor<Type, Ret (Class::*)(Args...) const> get_rid_of_noexcept(Ret (Class::*)(Args...) const);

    template<typename Ret, typename... Args, typename Class>
    static constexpr meta_function_descriptor<Type, Ret (Class::*)(Args...)> get_rid_of_noexcept(Ret (Class::*)(Args...));

    template<typename Ret, typename Class>
    static constexpr meta_function_descriptor<Type, Ret Class::*> get_rid_of_noexcept(Ret Class::*);

    template<typename Ret, typename... Args>
    static constexpr meta_function_descriptor<Type, Ret (*)(Args...)> get_rid_of_noexcept(Ret (*)(Args...));

    template<typename Class>
    static constexpr meta_function_descriptor<Class, decltype(&Class::operator())> get_rid_of_noexcept(Class);

public:
    /*! @brief The meta function descriptor of the given function. */
    using type = decltype(get_rid_of_noexcept(std::declval<Candidate>()));
};

/**
 * @brief Helper type.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Candidate The actual function to associate with the reflected type.
 */
template<typename Type, typename Candidate>
using meta_function_helper_t = typename meta_function_helper<Type, Candidate>::type;

/**
 * @brief Wraps a value depending on the given policy.
 *
 * This function always returns a wrapped value in the requested context.<br/>
 * Therefore, if the passed value is itself a wrapped object with a different
 * context, it undergoes a rebinding to the requested context.
 *
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Type Type of value to wrap.
 * @param ctx The context from which to search for meta types.
 * @param value Value to wrap.
 * @return A meta any containing the returned value, if any.
 */
template<typename Policy = as_is_t, typename Type>
std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_dispatch(const meta_ctx &ctx, [[maybe_unused]] Type &&value) {
    if constexpr(std::is_same_v<Policy, as_void_t>) {
        return meta_any{ctx, std::in_place_type<void>};
    } else if constexpr(std::is_same_v<Policy, as_ref_t>) {
        return meta_any{ctx, std::in_place_type<Type>, value};
    } else if constexpr(std::is_same_v<Policy, as_cref_t>) {
        static_assert(std::is_lvalue_reference_v<Type>, "Invalid type");
        return meta_any{ctx, std::in_place_type<const std::remove_reference_t<Type> &>, std::as_const(value)};
    } else {
        return meta_any{ctx, std::forward<Type>(value)};
    }
}

/**
 * @brief Wraps a value depending on the given policy.
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Type Type of value to wrap.
 * @param value Value to wrap.
 * @return A meta any containing the returned value, if any.
 */
template<typename Policy = as_is_t, typename Type>
std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_dispatch(Type &&value) {
    return meta_dispatch<Policy, Type>(locator<meta_ctx>::value_or(), std::forward<Type>(value));
}

/**
 * @brief Returns the meta type of the i-th element of a list of arguments.
 * @tparam Type Type list of the actual types of arguments.
 * @param ctx The context from which to search for meta types.
 * @param index The index of the element for which to return the meta type.
 * @return The meta type of the i-th element of the list of arguments.
 */
template<typename Type>
[[nodiscard]] static meta_type meta_arg(const meta_ctx &ctx, const std::size_t index) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    return {ctx, internal::meta_arg_node(context, Type{}, index)};
}

/**
 * @brief Returns the meta type of the i-th element of a list of arguments.
 * @tparam Type Type list of the actual types of arguments.
 * @param index The index of the element for which to return the meta type.
 * @return The meta type of the i-th element of the list of arguments.
 */
template<typename Type>
[[nodiscard]] static meta_type meta_arg(const std::size_t index) noexcept {
    return meta_arg<Type>(locator<meta_ctx>::value_or(), index);
}

/**
 * @brief Sets the value of a given variable.
 * @tparam Type Reflected type to which the variable is associated.
 * @tparam Data The actual variable to set.
 * @param instance An opaque instance of the underlying type, if required.
 * @param value Parameter to use to set the variable.
 * @return True in case of success, false otherwise.
 */
template<typename Type, auto Data>
[[nodiscard]] bool meta_setter([[maybe_unused]] meta_handle instance, [[maybe_unused]] meta_any value) {
    if constexpr(!std::is_same_v<decltype(Data), Type> && !std::is_same_v<decltype(Data), std::nullptr_t>) {
        if constexpr(std::is_member_function_pointer_v<decltype(Data)> || std::is_function_v<std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>>) {
            using descriptor = meta_function_helper_t<Type, decltype(Data)>;
            using data_type = type_list_element_t<descriptor::is_static, typename descriptor::args_type>;

            if(auto *const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
                std::invoke(Data, *clazz, value.cast<data_type>());
                return true;
            }
        } else if constexpr(std::is_member_object_pointer_v<decltype(Data)>) {
            using data_type = std::remove_reference_t<typename meta_function_helper_t<Type, decltype(Data)>::return_type>;

            if constexpr(!std::is_array_v<data_type> && !std::is_const_v<data_type>) {
                if(auto *const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
                    std::invoke(Data, *clazz) = value.cast<data_type>();
                    return true;
                }
            }
        } else {
            using data_type = std::remove_reference_t<decltype(*Data)>;

            if constexpr(!std::is_array_v<data_type> && !std::is_const_v<data_type>) {
                if(value.allow_cast<data_type>()) {
                    *Data = value.cast<data_type>();
                    return true;
                }
            }
        }
    }

    return false;
}

/**
 * @brief Gets the value of a given variable.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the variable is associated.
 * @tparam Data The actual variable to get.
 * @tparam Policy Optional policy (no policy set by default).
 * @param ctx The context from which to search for meta types.
 * @param instance An opaque instance of the underlying type, if required.
 * @return A meta any containing the value of the underlying variable.
 */
template<typename Type, auto Data, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_getter(const meta_ctx &ctx, [[maybe_unused]] meta_handle instance) {
    if constexpr(std::is_member_pointer_v<decltype(Data)> || std::is_function_v<std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>>) {
        if constexpr(!std::is_array_v<std::remove_cv_t<std::remove_reference_t<std::invoke_result_t<decltype(Data), Type &>>>>) {
            if constexpr(std::is_invocable_v<decltype(Data), Type &>) {
                if(auto *clazz = instance->try_cast<Type>(); clazz) {
                    return meta_dispatch<Policy>(ctx, std::invoke(Data, *clazz));
                }
            }

            if constexpr(std::is_invocable_v<decltype(Data), const Type &>) {
                if(auto *fallback = instance->try_cast<const Type>(); fallback) {
                    return meta_dispatch<Policy>(ctx, std::invoke(Data, *fallback));
                }
            }
        }

        return meta_any{meta_ctx_arg, ctx};
    } else if constexpr(std::is_pointer_v<decltype(Data)>) {
        if constexpr(std::is_array_v<std::remove_pointer_t<decltype(Data)>>) {
            return meta_any{meta_ctx_arg, ctx};
        } else {
            return meta_dispatch<Policy>(ctx, *Data);
        }
    } else {
        return meta_dispatch<Policy>(ctx, Data);
    }
}

/**
 * @brief Gets the value of a given variable.
 * @tparam Type Reflected type to which the variable is associated.
 * @tparam Data The actual variable to get.
 * @tparam Policy Optional policy (no policy set by default).
 * @param instance An opaque instance of the underlying type, if required.
 * @return A meta any containing the value of the underlying variable.
 */
template<typename Type, auto Data, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_getter(meta_handle instance) {
    return meta_getter<Type, Data, Policy>(locator<meta_ctx>::value_or(), std::move(instance));
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Policy, typename Candidate, typename... Args>
[[nodiscard]] meta_any meta_invoke_with_args(const meta_ctx &ctx, Candidate &&candidate, Args &&...args) {
    if constexpr(std::is_same_v<decltype(std::invoke(std::forward<Candidate>(candidate), args...)), void>) {
        std::invoke(std::forward<Candidate>(candidate), args...);
        return meta_any{ctx, std::in_place_type<void>};
    } else {
        return meta_dispatch<Policy>(ctx, std::invoke(std::forward<Candidate>(candidate), args...));
    }
}

template<typename Type, typename Policy, typename Candidate, std::size_t... Index>
[[nodiscard]] meta_any meta_invoke(const meta_ctx &ctx, [[maybe_unused]] meta_handle instance, Candidate &&candidate, [[maybe_unused]] meta_any *args, std::index_sequence<Index...>) {
    using descriptor = meta_function_helper_t<Type, std::remove_reference_t<Candidate>>;

    if constexpr(std::is_invocable_v<std::remove_reference_t<Candidate>, const Type &, type_list_element_t<Index, typename descriptor::args_type>...>) {
        if(const auto *const clazz = instance->try_cast<const Type>(); clazz && ((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
            return meta_invoke_with_args<Policy>(ctx, std::forward<Candidate>(candidate), *clazz, (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
        }
    } else if constexpr(std::is_invocable_v<std::remove_reference_t<Candidate>, Type &, type_list_element_t<Index, typename descriptor::args_type>...>) {
        if(auto *const clazz = instance->try_cast<Type>(); clazz && ((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
            return meta_invoke_with_args<Policy>(ctx, std::forward<Candidate>(candidate), *clazz, (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
        }
    } else {
        if(((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
            return meta_invoke_with_args<Policy>(ctx, std::forward<Candidate>(candidate), (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
        }
    }

    return meta_any{meta_ctx_arg, ctx};
}

template<typename Type, typename... Args, std::size_t... Index>
[[nodiscard]] meta_any meta_construct(const meta_ctx &ctx, meta_any *const args, std::index_sequence<Index...>) {
    if(((args + Index)->allow_cast<Args>() && ...)) {
        return meta_any{ctx, std::in_place_type<Type>, (args + Index)->cast<Args>()...};
    }

    return meta_any{meta_ctx_arg, ctx};
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Tries to _invoke_ an object given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the object to _invoke_ is associated.
 * @tparam Policy Optional policy (no policy set by default).
 * @param ctx The context from which to search for meta types.
 * @tparam Candidate The type of the actual object to _invoke_.
 * @param instance An opaque instance of the underlying type, if required.
 * @param candidate The actual object to _invoke_.
 * @param args Parameters to use to _invoke_ the object.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, typename Policy = as_is_t, typename Candidate>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_invoke(const meta_ctx &ctx, meta_handle instance, Candidate &&candidate, meta_any *const args) {
    return internal::meta_invoke<Type, Policy>(ctx, std::move(instance), std::forward<Candidate>(candidate), args, std::make_index_sequence<meta_function_helper_t<Type, std::remove_reference_t<Candidate>>::args_type::size>{});
}

/**
 * @brief Tries to _invoke_ an object given a list of erased parameters.
 * @tparam Type Reflected type to which the object to _invoke_ is associated.
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Candidate The type of the actual object to _invoke_.
 * @param instance An opaque instance of the underlying type, if required.
 * @param candidate The actual object to _invoke_.
 * @param args Parameters to use to _invoke_ the object.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, typename Policy = as_is_t, typename Candidate>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_invoke(meta_handle instance, Candidate &&candidate, meta_any *const args) {
    return meta_invoke<Type, Policy>(locator<meta_ctx>::value_or(), std::move(instance), std::forward<Candidate>(candidate), args);
}

/**
 * @brief Tries to invoke a function given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the function is associated.
 * @tparam Candidate The actual function to invoke.
 * @tparam Policy Optional policy (no policy set by default).
 * @param ctx The context from which to search for meta types.
 * @param instance An opaque instance of the underlying type, if required.
 * @param args Parameters to use to invoke the function.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, auto Candidate, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_invoke(const meta_ctx &ctx, meta_handle instance, meta_any *const args) {
    return internal::meta_invoke<Type, Policy>(ctx, std::move(instance), Candidate, args, std::make_index_sequence<meta_function_helper_t<Type, std::remove_reference_t<decltype(Candidate)>>::args_type::size>{});
}

/**
 * @brief Tries to invoke a function given a list of erased parameters.
 * @tparam Type Reflected type to which the function is associated.
 * @tparam Candidate The actual function to invoke.
 * @tparam Policy Optional policy (no policy set by default).
 * @param instance An opaque instance of the underlying type, if required.
 * @param args Parameters to use to invoke the function.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, auto Candidate, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_invoke(meta_handle instance, meta_any *const args) {
    return meta_invoke<Type, Candidate, Policy>(locator<meta_ctx>::value_or(), std::move(instance), args);
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Actual type of the instance to construct.
 * @tparam Args Types of arguments expected.
 * @param ctx The context from which to search for meta types.
 * @param args Parameters to use to construct the instance.
 * @return A meta any containing the new instance, if any.
 */
template<typename Type, typename... Args>
[[nodiscard]] meta_any meta_construct(const meta_ctx &ctx, meta_any *const args) {
    return internal::meta_construct<Type, Args...>(ctx, args, std::index_sequence_for<Args...>{});
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 * @tparam Type Actual type of the instance to construct.
 * @tparam Args Types of arguments expected.
 * @param args Parameters to use to construct the instance.
 * @return A meta any containing the new instance, if any.
 */
template<typename Type, typename... Args>
[[nodiscard]] meta_any meta_construct(meta_any *const args) {
    return meta_construct<Type, Args...>(locator<meta_ctx>::value_or(), args);
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the object to _invoke_ is associated.
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Candidate The type of the actual object to _invoke_.
 * @param ctx The context from which to search for meta types.
 * @param candidate The actual object to _invoke_.
 * @param args Parameters to use to _invoke_ the object.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, typename Policy = as_is_t, typename Candidate>
[[nodiscard]] meta_any meta_construct(const meta_ctx &ctx, Candidate &&candidate, meta_any *const args) {
    if constexpr(meta_function_helper_t<Type, Candidate>::is_static || std::is_class_v<std::remove_cv_t<std::remove_reference_t<Candidate>>>) {
        return internal::meta_invoke<Type, Policy>(ctx, {}, std::forward<Candidate>(candidate), args, std::make_index_sequence<meta_function_helper_t<Type, std::remove_reference_t<Candidate>>::args_type::size>{});
    } else {
        return internal::meta_invoke<Type, Policy>(ctx, *args, std::forward<Candidate>(candidate), args + 1u, std::make_index_sequence<meta_function_helper_t<Type, std::remove_reference_t<Candidate>>::args_type::size>{});
    }
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 * @tparam Type Reflected type to which the object to _invoke_ is associated.
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Candidate The type of the actual object to _invoke_.
 * @param candidate The actual object to _invoke_.
 * @param args Parameters to use to _invoke_ the object.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, typename Policy = as_is_t, typename Candidate>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_construct(Candidate &&candidate, meta_any *const args) {
    return meta_construct<Type, Policy>(locator<meta_ctx>::value_or(), std::forward<Candidate>(candidate), args);
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the function is associated.
 * @tparam Candidate The actual function to invoke.
 * @tparam Policy Optional policy (no policy set by default).
 * @param ctx The context from which to search for meta types.
 * @param args Parameters to use to invoke the function.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, auto Candidate, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_construct(const meta_ctx &ctx, meta_any *const args) {
    return meta_construct<Type, Policy>(ctx, Candidate, args);
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 * @tparam Type Reflected type to which the function is associated.
 * @tparam Candidate The actual function to invoke.
 * @tparam Policy Optional policy (no policy set by default).
 * @param args Parameters to use to invoke the function.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, auto Candidate, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_construct(meta_any *const args) {
    return meta_construct<Type, Candidate, Policy>(locator<meta_ctx>::value_or(), args);
}

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

inline decltype(auto) owner(meta_ctx &ctx, const type_info &info) {
    auto &&context = internal::meta_context::from(ctx);
    ENTT_ASSERT(context.value.contains(info.hash()), "Type not available");
    return context.value[info.hash()];
}

inline meta_base_node &meta_extend(internal::meta_type_node &parent, const id_type id, meta_base_node node) {
    return parent.details->base.insert_or_assign(id, std::move(node)).first->second;
}

inline meta_conv_node &meta_extend(internal::meta_type_node &parent, const id_type id, meta_conv_node node) {
    return parent.details->conv.insert_or_assign(id, std::move(node)).first->second;
}

inline meta_ctor_node &meta_extend(internal::meta_type_node &parent, const id_type id, meta_ctor_node node) {
    return parent.details->ctor.insert_or_assign(id, std::move(node)).first->second;
}

inline meta_dtor_node &meta_extend(internal::meta_type_node &parent, meta_dtor_node node) {
    return (parent.dtor = std::move(node));
}

inline meta_data_node &meta_extend(internal::meta_type_node &parent, const id_type id, meta_data_node node) {
    return parent.details->data.insert_or_assign(id, std::move(node)).first->second;
}

inline meta_func_node &meta_extend(internal::meta_type_node &parent, const id_type id, meta_func_node node) {
    if(auto it = parent.details->func.find(id); it != parent.details->func.end()) {
        for(auto *curr = &it->second; curr; curr = curr->next.get()) {
            if(curr->invoke == node.invoke) {
                node.next = std::move(curr->next);
                *curr = std::move(node);
                return *curr;
            }
        }

        // locally overloaded function
        node.next = std::make_shared<meta_func_node>(std::move(parent.details->func[id]));
    }

    return parent.details->func.insert_or_assign(id, std::move(node)).first->second;
}

inline meta_prop_node &meta_extend(dense_map<id_type, meta_prop_node, identity> &prop, const id_type id, meta_prop_node node) {
    return (prop[id] = std::move(node));
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic meta factory to be used for reflection purposes.
 * @tparam Type Reflected type for which the factory was created.
 */
template<typename Type>
class meta_factory {
    template<typename Setter, auto Getter, typename Policy, std::size_t... Index>
    void data(const id_type id, std::index_sequence<Index...>) noexcept {
        using data_type = std::invoke_result_t<decltype(Getter), Type &>;
        using args_type = type_list<typename meta_function_helper_t<Type, decltype(value_list_element_v<Index, Setter>)>::args_type...>;
        static_assert(Policy::template value<data_type>, "Invalid return type for the given policy");

        auto &&elem = internal::meta_extend(
            internal::owner(*ctx, *info),
            id,
            internal::meta_data_node{
                /* this is never static */
                (std::is_member_object_pointer_v<decltype(value_list_element_v<Index, Setter>)> && ... && std::is_const_v<std::remove_reference_t<data_type>>) ? internal::meta_traits::is_const : internal::meta_traits::is_none,
                Setter::size,
                &internal::resolve<std::remove_cv_t<std::remove_reference_t<data_type>>>,
                &meta_arg<type_list<type_list_element_t<type_list_element_t<Index, args_type>::size != 1u, type_list_element_t<Index, args_type>>...>>,
                +[](meta_handle instance, meta_any value) { return (meta_setter<Type, value_list_element_v<Index, Setter>>(*instance.operator->(), value.as_ref()) || ...); },
                &meta_getter<Type, Getter, Policy>});

        bucket = &elem.prop;
    }

public:
    /*! @brief Default constructor. */
    meta_factory() noexcept
        : meta_factory{locator<meta_ctx>::value_or()} {}

    /**
     * @brief Context aware constructor.
     * @param area The context into which to construct meta types.
     */
    meta_factory(meta_ctx &area) noexcept
        : ctx{&area},
          bucket{},
          info{&type_id<Type>()} {
        auto &&elem = internal::owner(*ctx, *info);

        if(!elem.details) {
            elem.details = std::make_shared<internal::meta_type_descriptor>();
        }

        bucket = &elem.details->prop;
    }

    /**
     * @brief Assigns a custom unique identifier to a meta type.
     * @param id A custom unique identifier.
     * @return An extended meta factory for the given type.
     */
    auto type(const id_type id) noexcept {
        auto &&elem = internal::owner(*ctx, *info);
        ENTT_ASSERT(elem.id == id || !resolve(*ctx, id), "Duplicate identifier");
        bucket = &elem.details->prop;
        elem.id = id;
        return *this;
    }

    /**
     * @brief Assigns a meta base to a meta type.
     *
     * A reflected base class must be a real base class of the reflected type.
     *
     * @tparam Base Type of the base class to assign to the meta type.
     * @return A meta factory for the parent type.
     */
    template<typename Base>
    auto base() noexcept {
        static_assert(!std::is_same_v<Type, Base> && std::is_base_of_v<Base, Type>, "Invalid base type");

        internal::meta_extend(
            internal::owner(*ctx, *info),
            type_id<Base>().hash(),
            internal::meta_base_node{
                &internal::resolve<Base>,
                +[](const void *instance) noexcept {
                    return static_cast<const void *>(static_cast<const Base *>(static_cast<const Type *>(instance)));
                }});

        bucket = nullptr;
        return *this;
    }

    /**
     * @brief Assigns a meta conversion function to a meta type.
     *
     * Conversion functions can be either free functions or member
     * functions.<br/>
     * In case of free functions, they must accept a const reference to an
     * instance of the parent type as an argument. In case of member functions,
     * they should have no arguments at all.
     *
     * @tparam Candidate The actual function to use for the conversion.
     * @return A meta factory for the parent type.
     */
    template<auto Candidate>
    auto conv() noexcept {
        using conv_type = std::remove_cv_t<std::remove_reference_t<std::invoke_result_t<decltype(Candidate), Type &>>>;

        internal::meta_extend(
            internal::owner(*ctx, *info),
            type_id<conv_type>().hash(),
            internal::meta_conv_node{
                +[](const meta_ctx &area, const void *instance) {
                    return forward_as_meta(area, std::invoke(Candidate, *static_cast<const Type *>(instance)));
                }});

        bucket = nullptr;
        return *this;
    }

    /**
     * @brief Assigns a meta conversion function to a meta type.
     *
     * The given type must be such that an instance of the reflected type can be
     * converted to it.
     *
     * @tparam To Type of the conversion function to assign to the meta type.
     * @return A meta factory for the parent type.
     */
    template<typename To>
    auto conv() noexcept {
        using conv_type = std::remove_cv_t<std::remove_reference_t<To>>;

        internal::meta_extend(
            internal::owner(*ctx, *info),
            type_id<conv_type>().hash(),
            internal::meta_conv_node{
                +[](const meta_ctx &area, const void *instance) {
                    return forward_as_meta(area, static_cast<To>(*static_cast<const Type *>(instance)));
                }});

        bucket = nullptr;
        return *this;
    }

    /**
     * @brief Assigns a meta constructor to a meta type.
     *
     * Both member functions and free function can be assigned to meta types in
     * the role of constructors. All that is required is that they return an
     * instance of the underlying type.<br/>
     * From a client's point of view, nothing changes if a constructor of a meta
     * type is a built-in one or not.
     *
     * @tparam Candidate The actual function to use as a constructor.
     * @tparam Policy Optional policy (no policy set by default).
     * @return An extended meta factory for the parent type.
     */
    template<auto Candidate, typename Policy = as_is_t>
    auto ctor() noexcept {
        using descriptor = meta_function_helper_t<Type, decltype(Candidate)>;
        static_assert(Policy::template value<typename descriptor::return_type>, "Invalid return type for the given policy");
        static_assert(std::is_same_v<std::remove_cv_t<std::remove_reference_t<typename descriptor::return_type>>, Type>, "The function doesn't return an object of the required type");

        internal::meta_extend(
            internal::owner(*ctx, *info),
            type_id<typename descriptor::args_type>().hash(),
            internal::meta_ctor_node{
                descriptor::args_type::size,
                &meta_arg<typename descriptor::args_type>,
                &meta_construct<Type, Candidate, Policy>});

        bucket = nullptr;
        return *this;
    }

    /**
     * @brief Assigns a meta constructor to a meta type.
     *
     * A meta constructor is uniquely identified by the types of its arguments
     * and is such that there exists an actual constructor of the underlying
     * type that can be invoked with parameters whose types are those given.
     *
     * @tparam Args Types of arguments to use to construct an instance.
     * @return An extended meta factory for the parent type.
     */
    template<typename... Args>
    auto ctor() noexcept {
        // default constructor is already implicitly generated, no need for redundancy
        if constexpr(sizeof...(Args) != 0u) {
            using descriptor = meta_function_helper_t<Type, Type (*)(Args...)>;

            internal::meta_extend(
                internal::owner(*ctx, *info),
                type_id<typename descriptor::args_type>().hash(),
                internal::meta_ctor_node{
                    descriptor::args_type::size,
                    &meta_arg<typename descriptor::args_type>,
                    &meta_construct<Type, Args...>});
        }

        bucket = nullptr;
        return *this;
    }

    /**
     * @brief Assigns a meta destructor to a meta type.
     *
     * Both free functions and member functions can be assigned to meta types in
     * the role of destructors.<br/>
     * The signature of a free function should be identical to the following:
     *
     * @code{.cpp}
     * void(Type &);
     * @endcode
     *
     * Member functions should not take arguments instead.<br/>
     * The purpose is to give users the ability to free up resources that
     * require special treatment before an object is actually destroyed.
     *
     * @tparam Func The actual function to use as a destructor.
     * @return A meta factory for the parent type.
     */
    template<auto Func>
    auto dtor() noexcept {
        static_assert(std::is_invocable_v<decltype(Func), Type &>, "The function doesn't accept an object of the type provided");

        internal::meta_extend(
            internal::owner(*ctx, *info),
            internal::meta_dtor_node{
                +[](void *instance) { std::invoke(Func, *static_cast<Type *>(instance)); }});

        bucket = nullptr;
        return *this;
    }

    /**
     * @brief Assigns a meta data to a meta type.
     *
     * Both data members and static and global variables, as well as constants
     * of any kind, can be assigned to a meta type.<br/>
     * From a client's point of view, all the variables associated with the
     * reflected object will appear as if they were part of the type itself.
     *
     * @tparam Data The actual variable to attach to the meta type.
     * @tparam Policy Optional policy (no policy set by default).
     * @param id Unique identifier.
     * @return An extended meta factory for the parent type.
     */
    template<auto Data, typename Policy = as_is_t>
    auto data(const id_type id) noexcept {
        if constexpr(std::is_member_object_pointer_v<decltype(Data)>) {
            using data_type = std::remove_reference_t<std::invoke_result_t<decltype(Data), Type &>>;

            auto &&elem = internal::meta_extend(
                internal::owner(*ctx, *info),
                id,
                internal::meta_data_node{
                    /* this is never static */
                    std::is_const_v<data_type> ? internal::meta_traits::is_const : internal::meta_traits::is_none,
                    1u,
                    &internal::resolve<std::remove_cv_t<data_type>>,
                    &meta_arg<type_list<std::remove_cv_t<data_type>>>,
                    &meta_setter<Type, Data>,
                    &meta_getter<Type, Data, Policy>});

            bucket = &elem.prop;
        } else {
            using data_type = std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>;

            auto &&elem = internal::meta_extend(
                internal::owner(*ctx, *info),
                id,
                internal::meta_data_node{
                    ((std::is_same_v<Type, std::remove_cv_t<data_type>> || std::is_const_v<data_type>) ? internal::meta_traits::is_const : internal::meta_traits::is_none) | internal::meta_traits::is_static,
                    1u,
                    &internal::resolve<std::remove_cv_t<data_type>>,
                    &meta_arg<type_list<std::remove_cv_t<data_type>>>,
                    &meta_setter<Type, Data>,
                    &meta_getter<Type, Data, Policy>});

            bucket = &elem.prop;
        }

        return *this;
    }

    /**
     * @brief Assigns a meta data to a meta type by means of its setter and
     * getter.
     *
     * Setters and getters can be either free functions, member functions or a
     * mix of them.<br/>
     * In case of free functions, setters and getters must accept a reference to
     * an instance of the parent type as their first argument. A setter has then
     * an extra argument of a type convertible to that of the parameter to
     * set.<br/>
     * In case of member functions, getters have no arguments at all, while
     * setters has an argument of a type convertible to that of the parameter to
     * set.
     *
     * @tparam Setter The actual function to use as a setter.
     * @tparam Getter The actual function to use as a getter.
     * @tparam Policy Optional policy (no policy set by default).
     * @param id Unique identifier.
     * @return An extended meta factory for the parent type.
     */
    template<auto Setter, auto Getter, typename Policy = as_is_t>
    auto data(const id_type id) noexcept {
        using data_type = std::invoke_result_t<decltype(Getter), Type &>;
        static_assert(Policy::template value<data_type>, "Invalid return type for the given policy");

        if constexpr(std::is_same_v<decltype(Setter), std::nullptr_t>) {
            auto &&elem = internal::meta_extend(
                internal::owner(*ctx, *info),
                id,
                internal::meta_data_node{
                    /* this is never static */
                    internal::meta_traits::is_const,
                    0u,
                    &internal::resolve<std::remove_cv_t<std::remove_reference_t<data_type>>>,
                    &meta_arg<type_list<>>,
                    &meta_setter<Type, Setter>,
                    &meta_getter<Type, Getter, Policy>});

            bucket = &elem.prop;
        } else {
            using args_type = typename meta_function_helper_t<Type, decltype(Setter)>::args_type;

            auto &&elem = internal::meta_extend(
                internal::owner(*ctx, *info),
                id,
                internal::meta_data_node{
                    /* this is never static nor const */
                    internal::meta_traits::is_none,
                    1u,
                    &internal::resolve<std::remove_cv_t<std::remove_reference_t<data_type>>>,
                    &meta_arg<type_list<type_list_element_t<args_type::size != 1u, args_type>>>,
                    &meta_setter<Type, Setter>,
                    &meta_getter<Type, Getter, Policy>});

            bucket = &elem.prop;
        }

        return *this;
    }

    /**
     * @brief Assigns a meta data to a meta type by means of its setters and
     * getter.
     *
     * Multi-setter support for meta data members. All setters are tried in the
     * order of definition before returning to the caller.<br/>
     * Setters can be either free functions, member functions or a mix of them
     * and are provided via a `value_list` type.
     *
     * @sa data
     *
     * @tparam Setter The actual functions to use as setters.
     * @tparam Getter The actual getter function.
     * @tparam Policy Optional policy (no policy set by default).
     * @param id Unique identifier.
     * @return An extended meta factory for the parent type.
     */
    template<typename Setter, auto Getter, typename Policy = as_is_t>
    auto data(const id_type id) noexcept {
        data<Setter, Getter, Policy>(id, std::make_index_sequence<Setter::size>{});
        return *this;
    }

    /**
     * @brief Assigns a meta function to a meta type.
     *
     * Both member functions and free functions can be assigned to a meta
     * type.<br/>
     * From a client's point of view, all the functions associated with the
     * reflected object will appear as if they were part of the type itself.
     *
     * @tparam Candidate The actual function to attach to the meta type.
     * @tparam Policy Optional policy (no policy set by default).
     * @param id Unique identifier.
     * @return An extended meta factory for the parent type.
     */
    template<auto Candidate, typename Policy = as_is_t>
    auto func(const id_type id) noexcept {
        using descriptor = meta_function_helper_t<Type, decltype(Candidate)>;
        static_assert(Policy::template value<typename descriptor::return_type>, "Invalid return type for the given policy");

        auto &&elem = internal::meta_extend(
            internal::owner(*ctx, *info),
            id,
            internal::meta_func_node{
                (descriptor::is_const ? internal::meta_traits::is_const : internal::meta_traits::is_none) | (descriptor::is_static ? internal::meta_traits::is_static : internal::meta_traits::is_none),
                descriptor::args_type::size,
                &internal::resolve<std::conditional_t<std::is_same_v<Policy, as_void_t>, void, std::remove_cv_t<std::remove_reference_t<typename descriptor::return_type>>>>,
                &meta_arg<typename descriptor::args_type>,
                &meta_invoke<Type, Candidate, Policy>});

        bucket = &elem.prop;
        return *this;
    }

    /**
     * @brief Assigns a property to the last meta object created.
     *
     * Both the key and the value (if any) must be at least copy constructible.
     *
     * @tparam Value Optional type of the property value.
     * @param id Property key.
     * @param value Optional property value.
     * @return An extended meta factory for the given type.
     */
    template<typename... Value>
    meta_factory prop(id_type id, [[maybe_unused]] Value &&...value) {
        ENTT_ASSERT(bucket != nullptr, "Meta object does not support properties");

        if constexpr(sizeof...(Value) == 0u) {
            internal::meta_extend(
                *bucket,
                id,
                internal::meta_prop_node{
                    &internal::resolve<void>});
        } else {
            internal::meta_extend(
                *bucket,
                id,
                internal::meta_prop_node{
                    &internal::resolve<std::decay_t<Value>>...,
                    std::make_shared<std::decay_t<Value>>(std::forward<Value>(value))...});
        }

        return *this;
    }

private:
    meta_ctx *ctx;
    dense_map<id_type, internal::meta_prop_node, identity> *bucket;
    const type_info *info;
};

/**
 * @brief Utility function to use for reflection.
 *
 * This is the point from which everything starts.<br/>
 * By invoking this function with a type that is not yet reflected, a meta type
 * is created to which it will be possible to attach meta objects through a
 * dedicated factory.
 *
 * @tparam Type Type to reflect.
 * @param ctx The context into which to construct meta types.
 * @return A meta factory for the given type.
 */
template<typename Type>
[[nodiscard]] auto meta(meta_ctx &ctx) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    // make sure the type exists in the context before returning a factory
    context.value.try_emplace(type_id<Type>().hash(), internal::resolve<Type>(context));
    return meta_factory<Type>{ctx};
}

/**
 * @brief Utility function to use for reflection.
 *
 * This is the point from which everything starts.<br/>
 * By invoking this function with a type that is not yet reflected, a meta type
 * is created to which it will be possible to attach meta objects through a
 * dedicated factory.
 *
 * @tparam Type Type to reflect.
 * @return A meta factory for the given type.
 */
template<typename Type>
[[nodiscard]] auto meta() noexcept {
    return meta<Type>(locator<meta_ctx>::value_or());
}

/**
 * @brief Resets a type and all its parts.
 *
 * Resets a type and all its data members, member functions and properties, as
 * well as its constructors, destructors and conversion functions if any.<br/>
 * Base classes aren't reset but the link between the two types is removed.
 *
 * The type is also removed from the set of searchable types.
 *
 * @param id Unique identifier.
 * @param ctx The context from which to reset meta types.
 */
inline void meta_reset(meta_ctx &ctx, const id_type id) noexcept {
    auto &&context = internal::meta_context::from(ctx);

    for(auto it = context.value.begin(); it != context.value.end();) {
        if(it->second.id == id) {
            it = context.value.erase(it);
        } else {
            ++it;
        }
    }
}

/**
 * @brief Resets a type and all its parts.
 *
 * Resets a type and all its data members, member functions and properties, as
 * well as its constructors, destructors and conversion functions if any.<br/>
 * Base classes aren't reset but the link between the two types is removed.
 *
 * The type is also removed from the set of searchable types.
 *
 * @param id Unique identifier.
 */
inline void meta_reset(const id_type id) noexcept {
    meta_reset(locator<meta_ctx>::value_or(), id);
}

/**
 * @brief Resets a type and all its parts.
 *
 * @sa meta_reset
 *
 * @tparam Type Type to reset.
 * @param ctx The context from which to reset meta types.
 */
template<typename Type>
void meta_reset(meta_ctx &ctx) noexcept {
    internal::meta_context::from(ctx).value.erase(type_id<Type>().hash());
}

/**
 * @brief Resets a type and all its parts.
 *
 * @sa meta_reset
 *
 * @tparam Type Type to reset.
 */
template<typename Type>
void meta_reset() noexcept {
    meta_reset<Type>(locator<meta_ctx>::value_or());
}

/**
 * @brief Resets all meta types.
 *
 * @sa meta_reset
 *
 * @param ctx The context from which to reset meta types.
 */
inline void meta_reset(meta_ctx &ctx) noexcept {
    internal::meta_context::from(ctx).value.clear();
}

/**
 * @brief Resets all meta types.
 *
 * @sa meta_reset
 */
inline void meta_reset() noexcept {
    meta_reset(locator<meta_ctx>::value_or());
}

} // namespace entt

#endif

// #include "meta/meta.hpp"
#ifndef ENTT_META_META_HPP
#define ENTT_META_META_HPP

#include <cstddef>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/any.hpp"

// #include "../core/fwd.hpp"

// #include "../core/iterator.hpp"

// #include "../core/type_info.hpp"

// #include "../core/type_traits.hpp"

// #include "../core/utility.hpp"

// #include "../locator/locator.hpp"

// #include "adl_pointer.hpp"

// #include "context.hpp"

// #include "fwd.hpp"

// #include "node.hpp"

// #include "range.hpp"

// #include "type_traits.hpp"


namespace entt {

class meta_any;
class meta_type;

/*! @brief Proxy object for sequence containers. */
class meta_sequence_container {
    class meta_iterator;

public:
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Meta iterator type. */
    using iterator = meta_iterator;

    /**
     * @brief Context aware constructor.
     * @param area The context from which to search for meta types.
     */
    meta_sequence_container(const meta_ctx &area = locator<meta_ctx>::value_or()) noexcept
        : ctx{&area} {}

    /**
     * @brief Rebinds a proxy object to a sequence container type.
     * @tparam Type Type of container to wrap.
     * @param instance The container to wrap.
     */
    template<typename Type>
    void rebind(any instance) noexcept {
        value_type_node = &internal::resolve<typename Type::value_type>;
        size_fn = &meta_sequence_container_traits<Type>::size;
        resize_fn = &meta_sequence_container_traits<Type>::resize;
        iter_fn = &meta_sequence_container_traits<Type>::iter;
        insert_or_erase_fn = &meta_sequence_container_traits<Type>::insert_or_erase;
        storage = std::move(instance);
    }

    [[nodiscard]] inline meta_type value_type() const noexcept;
    [[nodiscard]] inline size_type size() const noexcept;
    inline bool resize(const size_type);
    inline bool clear();
    [[nodiscard]] inline iterator begin();
    [[nodiscard]] inline iterator end();
    inline iterator insert(iterator, meta_any);
    inline iterator erase(iterator);
    [[nodiscard]] inline meta_any operator[](const size_type);
    [[nodiscard]] inline explicit operator bool() const noexcept;

private:
    const meta_ctx *ctx{};
    internal::meta_type_node (*value_type_node)(const internal::meta_context &){};
    size_type (*size_fn)(const any &) noexcept {};
    bool (*resize_fn)(any &, size_type){};
    iterator (*iter_fn)(const meta_ctx &, any &, const bool){};
    iterator (*insert_or_erase_fn)(const meta_ctx &, any &, const any &, meta_any &){};
    any storage{};
};

/*! @brief Proxy object for associative containers. */
class meta_associative_container {
    class meta_iterator;

public:
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Meta iterator type. */
    using iterator = meta_iterator;

    /**
     * @brief Context aware constructor.
     * @param area The context from which to search for meta types.
     */
    meta_associative_container(const meta_ctx &area = locator<meta_ctx>::value_or()) noexcept
        : ctx{&area} {}

    /**
     * @brief Rebinds a proxy object to an associative container type.
     * @tparam Type Type of container to wrap.
     * @param instance The container to wrap.
     */
    template<typename Type>
    void rebind(any instance) noexcept {
        if constexpr(!meta_associative_container_traits<Type>::key_only) {
            mapped_type_node = &internal::resolve<typename Type::mapped_type>;
        }

        key_only_container = meta_associative_container_traits<Type>::key_only;
        key_type_node = &internal::resolve<typename Type::key_type>;
        value_type_node = &internal::resolve<typename Type::value_type>;
        size_fn = &meta_associative_container_traits<Type>::size;
        clear_fn = &meta_associative_container_traits<Type>::clear;
        iter_fn = &meta_associative_container_traits<Type>::iter;
        insert_or_erase_fn = &meta_associative_container_traits<Type>::insert_or_erase;
        find_fn = &meta_associative_container_traits<Type>::find;
        storage = std::move(instance);
    }

    [[nodiscard]] inline bool key_only() const noexcept;
    [[nodiscard]] inline meta_type key_type() const noexcept;
    [[nodiscard]] inline meta_type mapped_type() const noexcept;
    [[nodiscard]] inline meta_type value_type() const noexcept;
    [[nodiscard]] inline size_type size() const noexcept;
    inline bool clear();
    [[nodiscard]] inline iterator begin();
    [[nodiscard]] inline iterator end();
    inline bool insert(meta_any);
    inline bool insert(meta_any, meta_any);
    inline size_type erase(meta_any);
    [[nodiscard]] inline iterator find(meta_any);
    [[nodiscard]] inline explicit operator bool() const noexcept;

private:
    const meta_ctx *ctx{};
    bool key_only_container{};
    internal::meta_type_node (*key_type_node)(const internal::meta_context &){};
    internal::meta_type_node (*mapped_type_node)(const internal::meta_context &){};
    internal::meta_type_node (*value_type_node)(const internal::meta_context &){};
    size_type (*size_fn)(const any &) noexcept {};
    bool (*clear_fn)(any &){};
    iterator (*iter_fn)(const meta_ctx &, any &, const bool){};
    size_type (*insert_or_erase_fn)(any &, meta_any &, meta_any &){};
    iterator (*find_fn)(const meta_ctx &, any &, meta_any &){};
    any storage{};
};

/*! @brief Opaque wrapper for values of any type. */
class meta_any {
    enum class operation : std::uint8_t {
        deref,
        seq,
        assoc
    };

    using vtable_type = void(const operation, const any &, void *);

    template<typename Type>
    static void basic_vtable([[maybe_unused]] const operation op, [[maybe_unused]] const any &value, [[maybe_unused]] void *other) {
        static_assert(std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, Type>, "Invalid type");

        if constexpr(!std::is_void_v<Type>) {
            switch(op) {
            case operation::deref:
                if constexpr(is_meta_pointer_like_v<Type>) {
                    if constexpr(std::is_function_v<typename std::pointer_traits<Type>::element_type>) {
                        static_cast<meta_any *>(other)->emplace<Type>(any_cast<Type>(value));
                    } else if constexpr(!std::is_same_v<std::remove_const_t<typename std::pointer_traits<Type>::element_type>, void>) {
                        using in_place_type = decltype(adl_meta_pointer_like<Type>::dereference(any_cast<const Type &>(value)));

                        if constexpr(std::is_constructible_v<bool, Type>) {
                            if(const auto &pointer_like = any_cast<const Type &>(value); pointer_like) {
                                static_cast<meta_any *>(other)->emplace<in_place_type>(adl_meta_pointer_like<Type>::dereference(pointer_like));
                            }
                        } else {
                            static_cast<meta_any *>(other)->emplace<in_place_type>(adl_meta_pointer_like<Type>::dereference(any_cast<const Type &>(value)));
                        }
                    }
                }
                break;
            case operation::seq:
                if constexpr(is_complete_v<meta_sequence_container_traits<Type>>) {
                    static_cast<meta_sequence_container *>(other)->rebind<Type>(std::move(const_cast<any &>(value)));
                }
                break;
            case operation::assoc:
                if constexpr(is_complete_v<meta_associative_container_traits<Type>>) {
                    static_cast<meta_associative_container *>(other)->rebind<Type>(std::move(const_cast<any &>(value)));
                }
                break;
            }
        }
    }

    void release() {
        if(node.dtor.dtor && owner()) {
            node.dtor.dtor(storage.data());
        }
    }

    meta_any(const meta_ctx &area, const meta_any &other, any ref) noexcept
        : storage{std::move(ref)},
          ctx{&area},
          node{storage ? other.node : internal::meta_type_node{}},
          vtable{storage ? other.vtable : &basic_vtable<void>} {}

public:
    /*! Default constructor. */
    meta_any() noexcept
        : meta_any{meta_ctx_arg, locator<meta_ctx>::value_or()} {}

    /**
     * @brief Context aware constructor.
     * @param area The context from which to search for meta types.
     */
    meta_any(meta_ctx_arg_t, const meta_ctx &area) noexcept
        : storage{},
          ctx{&area},
          node{},
          vtable{&basic_vtable<void>} {}

    /**
     * @brief Constructs a wrapper by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit meta_any(std::in_place_type_t<Type>, Args &&...args)
        : meta_any{locator<meta_ctx>::value_or(), std::in_place_type<Type>, std::forward<Args>(args)...} {}

    /**
     * @brief Constructs a wrapper by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param area The context from which to search for meta types.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit meta_any(const meta_ctx &area, std::in_place_type_t<Type>, Args &&...args)
        : storage{std::in_place_type<Type>, std::forward<Args>(args)...},
          ctx{&area},
          node{internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(internal::meta_context::from(*ctx))},
          vtable{&basic_vtable<std::remove_cv_t<std::remove_reference_t<Type>>>} {}

    /**
     * @brief Constructs a wrapper from a given value.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>>>
    meta_any(Type &&value)
        : meta_any{locator<meta_ctx>::value_or(), std::forward<Type>(value)} {}

    /**
     * @brief Constructs a wrapper from a given value.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param area The context from which to search for meta types.
     * @param value An instance of an object to use to initialize the wrapper.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>>>
    meta_any(const meta_ctx &area, Type &&value)
        : meta_any{area, std::in_place_type<std::decay_t<Type>>, std::forward<Type>(value)} {}

    /**
     * @brief Context aware copy constructor.
     * @param area The context from which to search for meta types.
     * @param other The instance to copy from.
     */
    meta_any(const meta_ctx &area, const meta_any &other)
        : meta_any{other} {
        ctx = &area;
        node = node.resolve ? node.resolve(internal::meta_context::from(*ctx)) : node;
    }

    /**
     * @brief Context aware move constructor.
     * @param area The context from which to search for meta types.
     * @param other The instance to move from.
     */
    meta_any(const meta_ctx &area, meta_any &&other)
        : meta_any{std::move(other)} {
        ctx = &area;
        node = node.resolve ? node.resolve(internal::meta_context::from(*ctx)) : node;
    }

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    meta_any(const meta_any &other) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    meta_any(meta_any &&other) noexcept
        : storage{std::move(other.storage)},
          ctx{other.ctx},
          node{std::exchange(other.node, internal::meta_type_node{})},
          vtable{std::exchange(other.vtable, &basic_vtable<void>)} {}

    /*! @brief Frees the internal storage, whatever it means. */
    ~meta_any() {
        release();
    }

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This meta any object.
     */
    meta_any &operator=(const meta_any &other) {
        release();
        storage = other.storage;
        ctx = other.ctx;
        node = other.node;
        vtable = other.vtable;
        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This meta any object.
     */
    meta_any &operator=(meta_any &&other) noexcept {
        release();
        storage = std::move(other.storage);
        ctx = other.ctx;
        node = std::exchange(other.node, internal::meta_type_node{});
        vtable = std::exchange(other.vtable, &basic_vtable<void>);
        return *this;
    }

    /**
     * @brief Value assignment operator.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     * @return This meta any object.
     */
    template<typename Type>
    std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_any>, meta_any &>
    operator=(Type &&value) {
        emplace<std::decay_t<Type>>(std::forward<Type>(value));
        return *this;
    }

    /*! @copydoc any::type */
    [[nodiscard]] inline meta_type type() const noexcept;

    /*! @copydoc any::data */
    [[nodiscard]] const void *data() const noexcept {
        return storage.data();
    }

    /*! @copydoc any::data */
    [[nodiscard]] void *data() noexcept {
        return storage.data();
    }

    /**
     * @brief Invokes the underlying function, if possible.
     * @tparam Args Types of arguments to use to invoke the function.
     * @param id Unique identifier.
     * @param args Parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    template<typename... Args>
    meta_any invoke(const id_type id, Args &&...args) const;

    /*! @copydoc invoke */
    template<typename... Args>
    meta_any invoke(const id_type id, Args &&...args);

    /**
     * @brief Sets the value of a given variable.
     * @tparam Type Type of value to assign.
     * @param id Unique identifier.
     * @param value Parameter to use to set the underlying variable.
     * @return True in case of success, false otherwise.
     */
    template<typename Type>
    bool set(const id_type id, Type &&value);

    /**
     * @brief Gets the value of a given variable.
     * @param id Unique identifier.
     * @return A wrapper containing the value of the underlying variable.
     */
    [[nodiscard]] meta_any get(const id_type id) const;

    /*! @copydoc get */
    [[nodiscard]] meta_any get(const id_type id);

    /**
     * @brief Tries to cast an instance to a given type.
     * @tparam Type Type to which to cast the instance.
     * @return A (possibly null) pointer to the contained instance.
     */
    template<typename Type>
    [[nodiscard]] const Type *try_cast() const {
        const auto other = internal::resolve<std::remove_cv_t<Type>>(internal::meta_context::from(*ctx));
        return static_cast<const Type *>(internal::try_cast(internal::meta_context::from(*ctx), node, other, data()));
    }

    /*! @copydoc try_cast */
    template<typename Type>
    [[nodiscard]] Type *try_cast() {
        if constexpr(std::is_const_v<Type>) {
            return std::as_const(*this).try_cast<std::remove_const_t<Type>>();
        } else {
            const auto other = internal::resolve<std::remove_cv_t<Type>>(internal::meta_context::from(*ctx));
            return static_cast<Type *>(const_cast<void *>(internal::try_cast(internal::meta_context::from(*ctx), node, other, data())));
        }
    }

    /**
     * @brief Tries to cast an instance to a given type.
     *
     * @warning
     * Attempting to perform an invalid cast results is undefined behavior.
     *
     * @tparam Type Type to which to cast the instance.
     * @return A reference to the contained instance.
     */
    template<typename Type>
    [[nodiscard]] Type cast() const {
        auto *const instance = try_cast<std::remove_reference_t<Type>>();
        ENTT_ASSERT(instance, "Invalid instance");
        return static_cast<Type>(*instance);
    }

    /*! @copydoc cast */
    template<typename Type>
    [[nodiscard]] Type cast() {
        // forces const on non-reference types to make them work also with wrappers for const references
        auto *const instance = try_cast<std::remove_reference_t<const Type>>();
        ENTT_ASSERT(instance, "Invalid instance");
        return static_cast<Type>(*instance);
    }

    /**
     * @brief Converts an object in such a way that a given cast becomes viable.
     * @param type Meta type to which the cast is requested.
     * @return A valid meta any object if there exists a viable conversion, an
     * invalid one otherwise.
     */
    [[nodiscard]] meta_any allow_cast(const meta_type &type) const;

    /**
     * @brief Converts an object in such a way that a given cast becomes viable.
     * @param type Meta type to which the cast is requested.
     * @return True if there exists a viable conversion, false otherwise.
     */
    [[nodiscard]] bool allow_cast(const meta_type &type) {
        if(auto other = std::as_const(*this).allow_cast(type); other) {
            if(other.owner()) {
                std::swap(*this, other);
            }

            return true;
        }

        return false;
    }

    /**
     * @brief Converts an object in such a way that a given cast becomes viable.
     * @tparam Type Type to which the cast is requested.
     * @return A valid meta any object if there exists a viable conversion, an
     * invalid one otherwise.
     */
    template<typename Type>
    [[nodiscard]] meta_any allow_cast() const {
        if constexpr(std::is_reference_v<Type> && !std::is_const_v<std::remove_reference_t<Type>>) {
            return meta_any{meta_ctx_arg, *ctx};
        } else {
            auto other = internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(internal::meta_context::from(*ctx));
            return allow_cast(meta_type{*ctx, other});
        }
    }

    /**
     * @brief Converts an object in such a way that a given cast becomes viable.
     * @tparam Type Type to which the cast is requested.
     * @return True if there exists a viable conversion, false otherwise.
     */
    template<typename Type>
    bool allow_cast() {
        auto other = internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(internal::meta_context::from(*ctx));
        return allow_cast(meta_type{*ctx, other}) && (!(std::is_reference_v<Type> && !std::is_const_v<std::remove_reference_t<Type>>) || storage.data() != nullptr);
    }

    /*! @copydoc any::emplace */
    template<typename Type, typename... Args>
    void emplace(Args &&...args) {
        release();
        storage.emplace<Type>(std::forward<Args>(args)...);
        node = internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(internal::meta_context::from(*ctx));
        vtable = &basic_vtable<std::remove_cv_t<std::remove_reference_t<Type>>>;
    }

    /*! @copydoc any::assign */
    bool assign(const meta_any &other);

    /*! @copydoc any::assign */
    bool assign(meta_any &&other);

    /*! @copydoc any::reset */
    void reset() {
        release();
        storage.reset();
        node = {};
        vtable = &basic_vtable<void>;
    }

    /**
     * @brief Returns a sequence container proxy.
     * @return A sequence container proxy for the underlying object.
     */
    [[nodiscard]] meta_sequence_container as_sequence_container() noexcept {
        any detached = storage.as_ref();
        meta_sequence_container proxy{*ctx};
        vtable(operation::seq, detached, &proxy);
        return proxy;
    }

    /*! @copydoc as_sequence_container */
    [[nodiscard]] meta_sequence_container as_sequence_container() const noexcept {
        any detached = storage.as_ref();
        meta_sequence_container proxy{*ctx};
        vtable(operation::seq, detached, &proxy);
        return proxy;
    }

    /**
     * @brief Returns an associative container proxy.
     * @return An associative container proxy for the underlying object.
     */
    [[nodiscard]] meta_associative_container as_associative_container() noexcept {
        any detached = storage.as_ref();
        meta_associative_container proxy{*ctx};
        vtable(operation::assoc, detached, &proxy);
        return proxy;
    }

    /*! @copydoc as_associative_container */
    [[nodiscard]] meta_associative_container as_associative_container() const noexcept {
        any detached = storage.as_ref();
        meta_associative_container proxy{*ctx};
        vtable(operation::assoc, detached, &proxy);
        return proxy;
    }

    /**
     * @brief Indirection operator for dereferencing opaque objects.
     * @return A wrapper that shares a reference to an unmanaged object if the
     * wrapped element is dereferenceable, an invalid meta any otherwise.
     */
    [[nodiscard]] meta_any operator*() const noexcept {
        meta_any ret{meta_ctx_arg, *ctx};
        vtable(operation::deref, storage, &ret);
        return ret;
    }

    /**
     * @brief Returns false if a wrapper is invalid, true otherwise.
     * @return False if the wrapper is invalid, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return !(node.info == nullptr);
    }

    /*! @copydoc any::operator== */
    [[nodiscard]] bool operator==(const meta_any &other) const noexcept {
        return (ctx == other.ctx) && ((!node.info && !other.node.info) || (node.info && other.node.info && *node.info == *other.node.info && storage == other.storage));
    }

    /*! @copydoc any::operator!= */
    [[nodiscard]] bool operator!=(const meta_any &other) const noexcept {
        return !(*this == other);
    }

    /*! @copydoc any::as_ref */
    [[nodiscard]] meta_any as_ref() noexcept {
        return meta_any{*ctx, *this, storage.as_ref()};
    }

    /*! @copydoc any::as_ref */
    [[nodiscard]] meta_any as_ref() const noexcept {
        return meta_any{*ctx, *this, storage.as_ref()};
    }

    /*! @copydoc any::owner */
    [[nodiscard]] bool owner() const noexcept {
        return storage.owner();
    }

private:
    any storage;
    const meta_ctx *ctx;
    internal::meta_type_node node;
    vtable_type *vtable;
};

/**
 * @brief Forwards its argument and avoids copies for lvalue references.
 * @tparam Type Type of argument to use to construct the new instance.
 * @param value Parameter to use to construct the instance.
 * @param ctx The context from which to search for meta types.
 * @return A properly initialized and not necessarily owning wrapper.
 */
template<typename Type>
meta_any forward_as_meta(const meta_ctx &ctx, Type &&value) {
    return meta_any{ctx, std::in_place_type<Type &&>, std::forward<Type>(value)};
}

/**
 * @brief Forwards its argument and avoids copies for lvalue references.
 * @tparam Type Type of argument to use to construct the new instance.
 * @param value Parameter to use to construct the instance.
 * @return A properly initialized and not necessarily owning wrapper.
 */
template<typename Type>
meta_any forward_as_meta(Type &&value) {
    return forward_as_meta(locator<meta_ctx>::value_or(), std::forward<Type>(value));
}

/**
 * @brief Opaque pointers to instances of any type.
 *
 * A handle doesn't perform copies and isn't responsible for the contained
 * object. It doesn't prolong the lifetime of the pointed instance.<br/>
 * Handles are used to generate references to actual objects when needed.
 */
struct meta_handle {
    /*! Default constructor. */
    meta_handle() noexcept
        : meta_handle{meta_ctx_arg, locator<meta_ctx>::value_or()} {}

    /**
     * @brief Context aware constructor.
     * @param area The context from which to search for meta types.
     */
    meta_handle(meta_ctx_arg_t, const meta_ctx &area) noexcept
        : any{meta_ctx_arg, area} {}

    /**
     * @brief Creates a handle that points to an unmanaged object.
     * @param value An instance of an object to use to initialize the handle.
     */
    meta_handle(meta_any &value) noexcept
        : any{value.as_ref()} {}

    /**
     * @brief Creates a handle that points to an unmanaged object.
     * @param value An instance of an object to use to initialize the handle.
     */
    meta_handle(const meta_any &value) noexcept
        : any{value.as_ref()} {}

    /**
     * @brief Creates a handle that points to an unmanaged object.
     * @tparam Type Type of object to use to initialize the handle.
     * @param ctx The context from which to search for meta types.
     * @param value An instance of an object to use to initialize the handle.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_handle>>>
    meta_handle(const meta_ctx &ctx, Type &value) noexcept
        : any{ctx, std::in_place_type<Type &>, value} {}

    /**
     * @brief Creates a handle that points to an unmanaged object.
     * @tparam Type Type of object to use to initialize the handle.
     * @param value An instance of an object to use to initialize the handle.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, meta_handle>>>
    meta_handle(Type &value) noexcept
        : meta_handle{locator<meta_ctx>::value_or(), value} {}

    /**
     * @brief Context aware copy constructor.
     * @param area The context from which to search for meta types.
     * @param other The instance to copy from.
     */
    meta_handle(const meta_ctx &area, const meta_handle &other)
        : any{area, other.any} {}

    /**
     * @brief Context aware move constructor.
     * @param area The context from which to search for meta types.
     * @param other The instance to move from.
     */
    meta_handle(const meta_ctx &area, meta_handle &&other)
        : any{area, std::move(other.any)} {}

    /*! @brief Default copy constructor, deleted on purpose. */
    meta_handle(const meta_handle &) = delete;

    /*! @brief Default move constructor. */
    meta_handle(meta_handle &&) = default;

    /**
     * @brief Default copy assignment operator, deleted on purpose.
     * @return This meta handle.
     */
    meta_handle &operator=(const meta_handle &) = delete;

    /**
     * @brief Default move assignment operator.
     * @return This meta handle.
     */
    meta_handle &operator=(meta_handle &&) = default;

    /**
     * @brief Returns false if a handle is invalid, true otherwise.
     * @return False if the handle is invalid, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(any);
    }

    /**
     * @brief Access operator for accessing the contained opaque object.
     * @return A wrapper that shares a reference to an unmanaged object.
     */
    [[nodiscard]] meta_any *operator->() {
        return &any;
    }

    /*! @copydoc operator-> */
    [[nodiscard]] const meta_any *operator->() const {
        return &any;
    }

private:
    meta_any any;
};

/*! @brief Opaque wrapper for properties of any type. */
struct meta_prop {
    /*! @brief Default constructor. */
    meta_prop() noexcept
        : node{},
          ctx{} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_prop(const meta_ctx &area, const internal::meta_prop_node &curr) noexcept
        : node{&curr},
          ctx{&area} {}

    /**
     * @brief Returns the stored value by copy.
     * @return A wrapper containing the value stored with the property.
     */
    [[nodiscard]] meta_any value() const {
        return node->value ? node->type(internal::meta_context::from(*ctx)).from_void(*ctx, nullptr, node->value.get()) : meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @brief Returns true if an object is valid, false otherwise.
     * @return True if the object is valid, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return (node != nullptr);
    }

private:
    const internal::meta_prop_node *node;
    const meta_ctx *ctx;
};

/*! @brief Opaque wrapper for data members. */
struct meta_data {
    /*! @brief Unsigned integer type. */
    using size_type = typename internal::meta_data_node::size_type;

    /*! @brief Default constructor. */
    meta_data() noexcept
        : node{},
          ctx{} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_data(const meta_ctx &area, const internal::meta_data_node &curr) noexcept
        : node{&curr},
          ctx{&area} {}

    /**
     * @brief Returns the number of setters available.
     * @return The number of setters available.
     */
    [[nodiscard]] size_type arity() const noexcept {
        return node->arity;
    }

    /**
     * @brief Indicates whether a data member is constant or not.
     * @return True if the data member is constant, false otherwise.
     */
    [[nodiscard]] bool is_const() const noexcept {
        return static_cast<bool>(node->traits & internal::meta_traits::is_const);
    }

    /**
     * @brief Indicates whether a data member is static or not.
     * @return True if the data member is static, false otherwise.
     */
    [[nodiscard]] bool is_static() const noexcept {
        return static_cast<bool>(node->traits & internal::meta_traits::is_static);
    }

    /*! @copydoc meta_any::type */
    [[nodiscard]] inline meta_type type() const noexcept;

    /**
     * @brief Sets the value of a given variable.
     * @tparam Type Type of value to assign.
     * @param instance An opaque instance of the underlying type.
     * @param value Parameter to use to set the underlying variable.
     * @return True in case of success, false otherwise.
     */
    template<typename Type>
    bool set(meta_handle instance, Type &&value) const {
        return node->set && node->set(meta_handle{*ctx, std::move(instance)}, meta_any{*ctx, std::forward<Type>(value)});
    }

    /**
     * @brief Gets the value of a given variable.
     * @param instance An opaque instance of the underlying type.
     * @return A wrapper containing the value of the underlying variable.
     */
    [[nodiscard]] meta_any get(meta_handle instance) const {
        return node->get(*ctx, meta_handle{*ctx, std::move(instance)});
    }

    /**
     * @brief Returns the type accepted by the i-th setter.
     * @param index Index of the setter of which to return the accepted type.
     * @return The type accepted by the i-th setter.
     */
    [[nodiscard]] inline meta_type arg(const size_type index) const noexcept;

    /**
     * @brief Returns a range to visit registered meta properties.
     * @return An iterable range to visit registered meta properties.
     */
    [[nodiscard]] meta_range<meta_prop, typename decltype(internal::meta_data_node::prop)::const_iterator> prop() const noexcept {
        return {{*ctx, node->prop.cbegin()}, {*ctx, node->prop.cend()}};
    }

    /**
     * @brief Lookup utility for meta properties.
     * @param key The key to use to search for a property.
     * @return The registered meta property for the given key, if any.
     */
    [[nodiscard]] meta_prop prop(const id_type key) const {
        const auto it = node->prop.find(key);
        return it != node->prop.cend() ? meta_prop{*ctx, it->second} : meta_prop{};
    }

    /**
     * @brief Returns true if an object is valid, false otherwise.
     * @return True if the object is valid, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return (node != nullptr);
    }

private:
    const internal::meta_data_node *node;
    const meta_ctx *ctx;
};

/*! @brief Opaque wrapper for member functions. */
struct meta_func {
    /*! @brief Unsigned integer type. */
    using size_type = typename internal::meta_func_node::size_type;

    /*! @brief Default constructor. */
    meta_func() noexcept
        : node{},
          ctx{} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_func(const meta_ctx &area, const internal::meta_func_node &curr) noexcept
        : node{&curr},
          ctx{&area} {}

    /**
     * @brief Returns the number of arguments accepted by a member function.
     * @return The number of arguments accepted by the member function.
     */
    [[nodiscard]] size_type arity() const noexcept {
        return node->arity;
    }

    /**
     * @brief Indicates whether a member function is constant or not.
     * @return True if the member function is constant, false otherwise.
     */
    [[nodiscard]] bool is_const() const noexcept {
        return static_cast<bool>(node->traits & internal::meta_traits::is_const);
    }

    /**
     * @brief Indicates whether a member function is static or not.
     * @return True if the member function is static, false otherwise.
     */
    [[nodiscard]] bool is_static() const noexcept {
        return static_cast<bool>(node->traits & internal::meta_traits::is_static);
    }

    /**
     * @brief Returns the return type of a member function.
     * @return The return type of the member function.
     */
    [[nodiscard]] inline meta_type ret() const noexcept;

    /**
     * @brief Returns the type of the i-th argument of a member function.
     * @param index Index of the argument of which to return the type.
     * @return The type of the i-th argument of a member function.
     */
    [[nodiscard]] inline meta_type arg(const size_type index) const noexcept;

    /**
     * @brief Invokes the underlying function, if possible.
     *
     * @warning
     * The context of the arguments is **not** changed.<br/>
     * It's up to the caller to bind them to the right context(s).
     *
     * @param instance An opaque instance of the underlying type.
     * @param args Parameters to use to invoke the function.
     * @param sz Number of parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    meta_any invoke(meta_handle instance, meta_any *const args, const size_type sz) const {
        return sz == arity() ? node->invoke(*ctx, meta_handle{*ctx, std::move(instance)}, args) : meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @copybrief invoke
     * @tparam Args Types of arguments to use to invoke the function.
     * @param instance An opaque instance of the underlying type.
     * @param args Parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    template<typename... Args>
    meta_any invoke(meta_handle instance, Args &&...args) const {
        meta_any arguments[sizeof...(Args) + 1u]{{*ctx, std::forward<Args>(args)}...};
        return invoke(meta_handle{*ctx, std::move(instance)}, arguments, sizeof...(Args));
    }

    /*! @copydoc meta_data::prop */
    [[nodiscard]] meta_range<meta_prop, typename decltype(internal::meta_func_node::prop)::const_iterator> prop() const noexcept {
        return {{*ctx, node->prop.cbegin()}, {*ctx, node->prop.cend()}};
    }

    /**
     * @brief Lookup utility for meta properties.
     * @param key The key to use to search for a property.
     * @return The registered meta property for the given key, if any.
     */
    [[nodiscard]] meta_prop prop(const id_type key) const {
        const auto it = node->prop.find(key);
        return it != node->prop.cend() ? meta_prop{*ctx, it->second} : meta_prop{};
    }

    /**
     * @brief Returns the next overload of a given function, if any.
     * @return The next overload of the given function, if any.
     */
    [[nodiscard]] meta_func next() const {
        return node->next ? meta_func{*ctx, *node->next} : meta_func{};
    }

    /**
     * @brief Returns true if an object is valid, false otherwise.
     * @return True if the object is valid, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return (node != nullptr);
    }

private:
    const internal::meta_func_node *node;
    const meta_ctx *ctx;
};

/*! @brief Opaque wrapper for types. */
class meta_type {
    template<typename Func>
    [[nodiscard]] auto lookup(meta_any *const args, const typename internal::meta_type_node::size_type sz, [[maybe_unused]] bool constness, Func next) const {
        decltype(next()) candidate = nullptr;
        size_type same{};
        bool ambiguous{};

        for(auto curr = next(); curr; curr = next()) {
            if constexpr(std::is_same_v<std::decay_t<decltype(*curr)>, internal::meta_func_node>) {
                if(constness && !static_cast<bool>(curr->traits & internal::meta_traits::is_const)) {
                    continue;
                }
            }

            if(curr->arity == sz) {
                size_type match{};
                size_type pos{};

                for(; pos < sz && args[pos]; ++pos) {
                    const auto other = curr->arg(*ctx, pos);
                    const auto type = args[pos].type();

                    if(const auto &info = other.info(); info == type.info()) {
                        ++match;
                    } else if(!((type.node.details && (type.node.details->base.contains(info.hash()) || type.node.details->conv.contains(info.hash()))) || (type.node.conversion_helper && other.node.conversion_helper))) {
                        break;
                    }
                }

                if(pos == sz) {
                    if(!candidate || match > same) {
                        candidate = curr;
                        same = match;
                        ambiguous = false;
                    } else if(match == same) {
                        if constexpr(std::is_same_v<std::decay_t<decltype(*curr)>, internal::meta_func_node>) {
                            if(static_cast<bool>(curr->traits & internal::meta_traits::is_const) != static_cast<bool>(candidate->traits & internal::meta_traits::is_const)) {
                                candidate = static_cast<bool>(candidate->traits & internal::meta_traits::is_const) ? curr : candidate;
                                ambiguous = false;
                                continue;
                            }
                        }

                        ambiguous = true;
                    }
                }
            }
        }

        return ambiguous ? nullptr : candidate;
    }

public:
    /*! @brief Unsigned integer type. */
    using size_type = typename internal::meta_type_node::size_type;

    /*! @brief Default constructor. */
    meta_type() noexcept
        : node{},
          ctx{} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_type(const meta_ctx &area, const internal::meta_type_node &curr) noexcept
        : node{curr},
          ctx{&area} {}

    /**
     * @brief Context aware constructor for meta objects.
     * @param area The context from which to search for meta types.
     * @param curr The underlying node with which to construct the instance.
     */
    meta_type(const meta_ctx &area, const internal::meta_base_node &curr) noexcept
        : meta_type{area, curr.type(internal::meta_context::from(area))} {}

    /**
     * @brief Returns the type info object of the underlying type.
     * @return The type info object of the underlying type.
     */
    [[nodiscard]] const type_info &info() const noexcept {
        return *node.info;
    }

    /**
     * @brief Returns the identifier assigned to a type.
     * @return The identifier assigned to the type.
     */
    [[nodiscard]] id_type id() const noexcept {
        return node.id;
    }

    /**
     * @brief Returns the size of the underlying type if known.
     * @return The size of the underlying type if known, 0 otherwise.
     */
    [[nodiscard]] size_type size_of() const noexcept {
        return node.size_of;
    }

    /**
     * @brief Checks whether a type refers to an arithmetic type or not.
     * @return True if the underlying type is an arithmetic type, false
     * otherwise.
     */
    [[nodiscard]] bool is_arithmetic() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_arithmetic);
    }

    /**
     * @brief Checks whether a type refers to an integral type or not.
     * @return True if the underlying type is an integral type, false otherwise.
     */
    [[nodiscard]] bool is_integral() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_integral);
    }

    /**
     * @brief Checks whether a type refers to a signed type or not.
     * @return True if the underlying type is a signed type, false otherwise.
     */
    [[nodiscard]] bool is_signed() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_signed);
    }

    /**
     * @brief Checks whether a type refers to an array type or not.
     * @return True if the underlying type is an array type, false otherwise.
     */
    [[nodiscard]] bool is_array() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_array);
    }

    /**
     * @brief Checks whether a type refers to an enum or not.
     * @return True if the underlying type is an enum, false otherwise.
     */
    [[nodiscard]] bool is_enum() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_enum);
    }

    /**
     * @brief Checks whether a type refers to a class or not.
     * @return True if the underlying type is a class, false otherwise.
     */
    [[nodiscard]] bool is_class() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_class);
    }

    /**
     * @brief Checks whether a type refers to a pointer or not.
     * @return True if the underlying type is a pointer, false otherwise.
     */
    [[nodiscard]] bool is_pointer() const noexcept {
        return node.info && (node.info->hash() != remove_pointer().info().hash());
    }

    /**
     * @brief Provides the type for which the pointer is defined.
     * @return The type for which the pointer is defined or this type if it
     * doesn't refer to a pointer type.
     */
    [[nodiscard]] meta_type remove_pointer() const noexcept {
        return {*ctx, node.remove_pointer(internal::meta_context::from(*ctx))};
    }

    /**
     * @brief Checks whether a type is a pointer-like type or not.
     * @return True if the underlying type is a pointer-like one, false
     * otherwise.
     */
    [[nodiscard]] bool is_pointer_like() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_meta_pointer_like);
    }

    /**
     * @brief Checks whether a type refers to a sequence container or not.
     * @return True if the type is a sequence container, false otherwise.
     */
    [[nodiscard]] bool is_sequence_container() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_meta_sequence_container);
    }

    /**
     * @brief Checks whether a type refers to an associative container or not.
     * @return True if the type is an associative container, false otherwise.
     */
    [[nodiscard]] bool is_associative_container() const noexcept {
        return static_cast<bool>(node.traits & internal::meta_traits::is_meta_associative_container);
    }

    /**
     * @brief Checks whether a type refers to a recognized class template
     * specialization or not.
     * @return True if the type is a recognized class template specialization,
     * false otherwise.
     */
    [[nodiscard]] bool is_template_specialization() const noexcept {
        return (node.templ.arity != 0u);
    }

    /**
     * @brief Returns the number of template arguments.
     * @return The number of template arguments.
     */
    [[nodiscard]] size_type template_arity() const noexcept {
        return node.templ.arity;
    }

    /**
     * @brief Returns a tag for the class template of the underlying type.
     * @return The tag for the class template of the underlying type.
     */
    [[nodiscard]] inline meta_type template_type() const noexcept {
        return node.templ.type ? meta_type{*ctx, node.templ.type(internal::meta_context::from(*ctx))} : meta_type{};
    }

    /**
     * @brief Returns the type of the i-th template argument of a type.
     * @param index Index of the template argument of which to return the type.
     * @return The type of the i-th template argument of a type.
     */
    [[nodiscard]] inline meta_type template_arg(const size_type index) const noexcept {
        return index < template_arity() ? meta_type{*ctx, node.templ.arg(internal::meta_context::from(*ctx), index)} : meta_type{};
    }

    /**
     * @brief Returns a range to visit registered top-level base meta types.
     * @return An iterable range to visit registered top-level base meta types.
     */
    [[nodiscard]] meta_range<meta_type, typename decltype(internal::meta_type_descriptor::base)::const_iterator> base() const noexcept {
        using range_type = meta_range<meta_type, typename decltype(internal::meta_type_descriptor::base)::const_iterator>;
        return node.details ? range_type{{*ctx, node.details->base.cbegin()}, {*ctx, node.details->base.cend()}} : range_type{};
    }

    /**
     * @brief Returns a range to visit registered top-level meta data.
     * @return An iterable range to visit registered top-level meta data.
     */
    [[nodiscard]] meta_range<meta_data, typename decltype(internal::meta_type_descriptor::data)::const_iterator> data() const noexcept {
        using range_type = meta_range<meta_data, typename decltype(internal::meta_type_descriptor::data)::const_iterator>;
        return node.details ? range_type{{*ctx, node.details->data.cbegin()}, {*ctx, node.details->data.cend()}} : range_type{};
    }

    /**
     * @brief Lookup utility for meta data (bases are also visited).
     * @param id Unique identifier.
     * @return The registered meta data for the given identifier, if any.
     */
    [[nodiscard]] meta_data data(const id_type id) const {
        if(node.details) {
            if(const auto it = node.details->data.find(id); it != node.details->data.cend()) {
                return meta_data{*ctx, it->second};
            }
        }

        for(auto &&curr: base()) {
            if(auto elem = curr.second.data(id); elem) {
                return elem;
            }
        }

        return meta_data{};
    }

    /**
     * @brief Returns a range to visit registered top-level functions.
     * @return An iterable range to visit registered top-level functions.
     */
    [[nodiscard]] meta_range<meta_func, typename decltype(internal::meta_type_descriptor::func)::const_iterator> func() const noexcept {
        using return_type = meta_range<meta_func, typename decltype(internal::meta_type_descriptor::func)::const_iterator>;
        return node.details ? return_type{{*ctx, node.details->func.cbegin()}, {*ctx, node.details->func.cend()}} : return_type{};
    }

    /**
     * @brief Lookup utility for meta functions (bases are also visited).
     *
     * In case of overloaded functions, the first one with the required
     * identifier is returned.
     *
     * @param id Unique identifier.
     * @return The registered meta function for the given identifier, if any.
     */
    [[nodiscard]] meta_func func(const id_type id) const {
        if(node.details) {
            if(const auto it = node.details->func.find(id); it != node.details->func.cend()) {
                return meta_func{*ctx, it->second};
            }
        }

        for(auto &&curr: base()) {
            if(auto elem = curr.second.func(id); elem) {
                return elem;
            }
        }

        return meta_func{};
    }

    /**
     * @brief Creates an instance of the underlying type, if possible.
     *
     * If suitable, the implicitly generated default constructor is used.
     *
     * @warning
     * The context of the arguments is **not** changed.<br/>
     * It's up to the caller to bind them to the right context(s).
     *
     * @param args Parameters to use to construct the instance.
     * @param sz Number of parameters to use to construct the instance.
     * @return A wrapper containing the new instance, if any.
     */
    [[nodiscard]] meta_any construct(meta_any *const args, const size_type sz) const {
        if(node.details) {
            if(const auto *candidate = lookup(args, sz, false, [first = node.details->ctor.cbegin(), last = node.details->ctor.cend()]() mutable { return first == last ? nullptr : &(first++)->second; }); candidate) {
                return candidate->invoke(*ctx, args);
            }
        }

        if(sz == 0u && node.default_constructor) {
            return node.default_constructor(*ctx);
        }

        return meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @copybrief construct
     * @tparam Args Types of arguments to use to construct the instance.
     * @param args Parameters to use to construct the instance.
     * @return A wrapper containing the new instance, if any.
     */
    template<typename... Args>
    [[nodiscard]] meta_any construct(Args &&...args) const {
        meta_any arguments[sizeof...(Args) + 1u]{{*ctx, std::forward<Args>(args)}...};
        return construct(arguments, sizeof...(Args));
    }

    /**
     * @brief Wraps an opaque element of the underlying type.
     * @param element A valid pointer to an element of the underlying type.
     * @return A wrapper that references the given instance.
     */
    meta_any from_void(void *element) const {
        return (element && node.from_void) ? node.from_void(*ctx, element, nullptr) : meta_any{meta_ctx_arg, *ctx};
    }

    /*! @copydoc from_void */
    meta_any from_void(const void *element) const {
        return (element && node.from_void) ? node.from_void(*ctx, nullptr, element) : meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @brief Invokes a function given an identifier, if possible.
     *
     * @warning
     * The context of the arguments is **not** changed.<br/>
     * It's up to the caller to bind them to the right context(s).
     *
     * @param id Unique identifier.
     * @param instance An opaque instance of the underlying type.
     * @param args Parameters to use to invoke the function.
     * @param sz Number of parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    meta_any invoke(const id_type id, meta_handle instance, meta_any *const args, const size_type sz) const {
        if(node.details) {
            if(auto it = node.details->func.find(id); it != node.details->func.cend()) {
                if(const auto *candidate = lookup(args, sz, (instance->data() == nullptr), [curr = &it->second]() mutable { return curr ? std::exchange(curr, curr->next.get()) : nullptr; }); candidate) {
                    return candidate->invoke(*ctx, meta_handle{*ctx, std::move(instance)}, args);
                }
            }
        }

        for(auto &&curr: base()) {
            if(auto elem = curr.second.invoke(id, *instance.operator->(), args, sz); elem) {
                return elem;
            }
        }

        return meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @copybrief invoke
     *
     * @param id Unique identifier.
     * @tparam Args Types of arguments to use to invoke the function.
     * @param instance An opaque instance of the underlying type.
     * @param args Parameters to use to invoke the function.
     * @return A wrapper containing the returned value, if any.
     */
    template<typename... Args>
    meta_any invoke(const id_type id, meta_handle instance, Args &&...args) const {
        meta_any arguments[sizeof...(Args) + 1u]{{*ctx, std::forward<Args>(args)}...};
        return invoke(id, meta_handle{*ctx, std::move(instance)}, arguments, sizeof...(Args));
    }

    /**
     * @brief Sets the value of a given variable.
     * @tparam Type Type of value to assign.
     * @param id Unique identifier.
     * @param instance An opaque instance of the underlying type.
     * @param value Parameter to use to set the underlying variable.
     * @return True in case of success, false otherwise.
     */
    template<typename Type>
    bool set(const id_type id, meta_handle instance, Type &&value) const {
        const auto candidate = data(id);
        return candidate && candidate.set(std::move(instance), std::forward<Type>(value));
    }

    /**
     * @brief Gets the value of a given variable.
     * @param id Unique identifier.
     * @param instance An opaque instance of the underlying type.
     * @return A wrapper containing the value of the underlying variable.
     */
    [[nodiscard]] meta_any get(const id_type id, meta_handle instance) const {
        const auto candidate = data(id);
        return candidate ? candidate.get(std::move(instance)) : meta_any{meta_ctx_arg, *ctx};
    }

    /**
     * @brief Returns a range to visit registered top-level meta properties.
     * @return An iterable range to visit registered top-level meta properties.
     */
    [[nodiscard]] meta_range<meta_prop, typename decltype(internal::meta_type_descriptor::prop)::const_iterator> prop() const noexcept {
        using range_type = meta_range<meta_prop, typename decltype(internal::meta_type_descriptor::prop)::const_iterator>;
        return node.details ? range_type{{*ctx, node.details->prop.cbegin()}, {*ctx, node.details->prop.cend()}} : range_type{};
    }

    /**
     * @brief Lookup utility for meta properties (bases are also visited).
     * @param key The key to use to search for a property.
     * @return The registered meta property for the given key, if any.
     */
    [[nodiscard]] meta_prop prop(const id_type key) const {
        if(node.details) {
            if(const auto it = node.details->prop.find(key); it != node.details->prop.cend()) {
                return meta_prop{*ctx, it->second};
            }
        }

        for(auto &&curr: base()) {
            if(auto elem = curr.second.prop(key); elem) {
                return elem;
            }
        }

        return meta_prop{};
    }

    /**
     * @brief Returns true if an object is valid, false otherwise.
     * @return True if the object is valid, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return !(ctx == nullptr);
    }

    /**
     * @brief Checks if two objects refer to the same type.
     * @param other The object with which to compare.
     * @return True if the objects refer to the same type, false otherwise.
     */
    [[nodiscard]] bool operator==(const meta_type &other) const noexcept {
        return (ctx == other.ctx) && ((!node.info && !other.node.info) || (node.info && other.node.info && *node.info == *other.node.info));
    }

private:
    internal::meta_type_node node;
    const meta_ctx *ctx;
};

/**
 * @brief Checks if two objects refer to the same type.
 * @param lhs An object, either valid or not.
 * @param rhs An object, either valid or not.
 * @return False if the objects refer to the same node, true otherwise.
 */
[[nodiscard]] inline bool operator!=(const meta_type &lhs, const meta_type &rhs) noexcept {
    return !(lhs == rhs);
}

[[nodiscard]] inline meta_type meta_any::type() const noexcept {
    return node.info ? meta_type{*ctx, node} : meta_type{};
}

template<typename... Args>
meta_any meta_any::invoke(const id_type id, Args &&...args) const {
    return type().invoke(id, *this, std::forward<Args>(args)...);
}

template<typename... Args>
meta_any meta_any::invoke(const id_type id, Args &&...args) {
    return type().invoke(id, *this, std::forward<Args>(args)...);
}

template<typename Type>
bool meta_any::set(const id_type id, Type &&value) {
    return type().set(id, *this, std::forward<Type>(value));
}

[[nodiscard]] inline meta_any meta_any::get(const id_type id) const {
    return type().get(id, *this);
}

[[nodiscard]] inline meta_any meta_any::get(const id_type id) {
    return type().get(id, *this);
}

[[nodiscard]] inline meta_any meta_any::allow_cast(const meta_type &type) const {
    if(node.info && *node.info == type.info()) {
        return as_ref();
    }

    if(const auto *value = data(); node.details) {
        if(auto it = node.details->conv.find(type.info().hash()); it != node.details->conv.cend()) {
            return it->second.conv(*ctx, data());
        }

        for(auto &&curr: node.details->base) {
            const auto &as_const = curr.second.type(internal::meta_context::from(*ctx)).from_void(*ctx, nullptr, curr.second.cast(value));

            if(auto other = as_const.allow_cast(type); other) {
                return other;
            }
        }
    }

    if(node.conversion_helper && (type.is_arithmetic() || type.is_enum())) {
        // exploits the fact that arithmetic types and enums are also default constructible
        auto other = type.construct();
        ENTT_ASSERT(other.node.conversion_helper, "Conversion helper not found");
        const auto value = node.conversion_helper(nullptr, storage.data());
        other.node.conversion_helper(other.storage.data(), &value);
        return other;
    }

    return meta_any{meta_ctx_arg, *ctx};
}

inline bool meta_any::assign(const meta_any &other) {
    auto value = other.allow_cast({*ctx, node});
    return value && storage.assign(std::move(value.storage));
}

inline bool meta_any::assign(meta_any &&other) {
    if(*node.info == *other.node.info) {
        return storage.assign(std::move(other.storage));
    }

    return assign(std::as_const(other));
}

[[nodiscard]] inline meta_type meta_data::type() const noexcept {
    return meta_type{*ctx, node->type(internal::meta_context::from(*ctx))};
}

[[nodiscard]] inline meta_type meta_data::arg(const size_type index) const noexcept {
    return index < arity() ? node->arg(*ctx, index) : meta_type{};
}

[[nodiscard]] inline meta_type meta_func::ret() const noexcept {
    return meta_type{*ctx, node->ret(internal::meta_context::from(*ctx))};
}

[[nodiscard]] inline meta_type meta_func::arg(const size_type index) const noexcept {
    return index < arity() ? node->arg(*ctx, index) : meta_type{};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

class meta_sequence_container::meta_iterator final {
    friend class meta_sequence_container;

    enum class operation : std::uint8_t {
        incr,
        deref
    };

    using vtable_type = void(const operation, const any &, const std::ptrdiff_t, meta_any *);

    template<typename It>
    static void basic_vtable(const operation op, const any &value, const std::ptrdiff_t offset, meta_any *other) {
        switch(op) {
        case operation::incr: {
            auto &it = any_cast<It &>(const_cast<any &>(value));
            it = std::next(it, offset);
        } break;
        case operation::deref: {
            const auto &it = any_cast<const It &>(value);
            other->emplace<decltype(*it)>(*it);
        } break;
        }
    }

public:
    using difference_type = std::ptrdiff_t;
    using value_type = meta_any;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    constexpr meta_iterator() noexcept
        : ctx{},
          vtable{},
          handle{} {}

    template<typename It>
    explicit meta_iterator(const meta_ctx &area, It iter) noexcept
        : ctx{&area},
          vtable{&basic_vtable<It>},
          handle{std::move(iter)} {}

    meta_iterator &operator++() noexcept {
        vtable(operation::incr, handle, 1, nullptr);
        return *this;
    }

    meta_iterator operator++(int value) noexcept {
        meta_iterator orig = *this;
        vtable(operation::incr, handle, ++value, nullptr);
        return orig;
    }

    meta_iterator &operator--() noexcept {
        vtable(operation::incr, handle, -1, nullptr);
        return *this;
    }

    meta_iterator operator--(int value) noexcept {
        meta_iterator orig = *this;
        vtable(operation::incr, handle, --value, nullptr);
        return orig;
    }

    [[nodiscard]] reference operator*() const {
        reference other{meta_ctx_arg, *ctx};
        vtable(operation::deref, handle, 0, &other);
        return other;
    }

    [[nodiscard]] pointer operator->() const {
        return operator*();
    }

    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(handle);
    }

    [[nodiscard]] bool operator==(const meta_iterator &other) const noexcept {
        return handle == other.handle;
    }

    [[nodiscard]] bool operator!=(const meta_iterator &other) const noexcept {
        return !(*this == other);
    }

private:
    const meta_ctx *ctx;
    vtable_type *vtable;
    any handle;
};

class meta_associative_container::meta_iterator final {
    enum class operation : std::uint8_t {
        incr,
        deref
    };

    using vtable_type = void(const operation, const any &, std::pair<meta_any, meta_any> *);

    template<bool KeyOnly, typename It>
    static void basic_vtable(const operation op, const any &value, std::pair<meta_any, meta_any> *other) {
        switch(op) {
        case operation::incr:
            ++any_cast<It &>(const_cast<any &>(value));
            break;
        case operation::deref:
            const auto &it = any_cast<const It &>(value);
            if constexpr(KeyOnly) {
                other->first.emplace<decltype(*it)>(*it);
            } else {
                other->first.emplace<decltype((it->first))>(it->first);
                other->second.emplace<decltype((it->second))>(it->second);
            }
            break;
        }
    }

public:
    using difference_type = std::ptrdiff_t;
    using value_type = std::pair<meta_any, meta_any>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    constexpr meta_iterator() noexcept
        : ctx{},
          vtable{},
          handle{} {}

    template<bool KeyOnly, typename It>
    meta_iterator(const meta_ctx &area, std::integral_constant<bool, KeyOnly>, It iter) noexcept
        : ctx{&area},
          vtable{&basic_vtable<KeyOnly, It>},
          handle{std::move(iter)} {}

    meta_iterator &operator++() noexcept {
        vtable(operation::incr, handle, nullptr);
        return *this;
    }

    meta_iterator operator++(int) noexcept {
        meta_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] reference operator*() const {
        reference other{{meta_ctx_arg, *ctx}, {meta_ctx_arg, *ctx}};
        vtable(operation::deref, handle, &other);
        return other;
    }

    [[nodiscard]] pointer operator->() const {
        return operator*();
    }

    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(handle);
    }

    [[nodiscard]] bool operator==(const meta_iterator &other) const noexcept {
        return handle == other.handle;
    }

    [[nodiscard]] bool operator!=(const meta_iterator &other) const noexcept {
        return !(*this == other);
    }

private:
    const meta_ctx *ctx;
    vtable_type *vtable;
    any handle;
};

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Returns the meta value type of a container.
 * @return The meta value type of the container.
 */
[[nodiscard]] inline meta_type meta_sequence_container::value_type() const noexcept {
    return value_type_node ? meta_type{*ctx, value_type_node(internal::meta_context::from(*ctx))} : meta_type{};
}

/**
 * @brief Returns the size of a container.
 * @return The size of the container.
 */
[[nodiscard]] inline meta_sequence_container::size_type meta_sequence_container::size() const noexcept {
    return size_fn(storage);
}

/**
 * @brief Resizes a container to contain a given number of elements.
 * @param sz The new size of the container.
 * @return True in case of success, false otherwise.
 */
inline bool meta_sequence_container::resize(const size_type sz) {
    return resize_fn(storage, sz);
}

/**
 * @brief Clears the content of a container.
 * @return True in case of success, false otherwise.
 */
inline bool meta_sequence_container::clear() {
    return resize_fn(storage, 0u);
}

/**
 * @brief Returns an iterator to the first element of a container.
 * @return An iterator to the first element of the container.
 */
[[nodiscard]] inline meta_sequence_container::iterator meta_sequence_container::begin() {
    return iter_fn(*ctx, storage, false);
}

/**
 * @brief Returns an iterator that is past the last element of a container.
 * @return An iterator that is past the last element of the container.
 */
[[nodiscard]] inline meta_sequence_container::iterator meta_sequence_container::end() {
    return iter_fn(*ctx, storage, true);
}

/**
 * @brief Inserts an element at a specified location of a container.
 * @param it Iterator before which the element will be inserted.
 * @param value Element value to insert.
 * @return A possibly invalid iterator to the inserted element.
 */
inline meta_sequence_container::iterator meta_sequence_container::insert(iterator it, meta_any value) {
    return insert_or_erase_fn(*ctx, storage, it.handle, value);
}

/**
 * @brief Removes a given element from a container.
 * @param it Iterator to the element to remove.
 * @return A possibly invalid iterator following the last removed element.
 */
inline meta_sequence_container::iterator meta_sequence_container::erase(iterator it) {
    return insert(std::move(it), {});
}

/**
 * @brief Returns a reference to the element at a given location of a container
 * (no bounds checking is performed).
 * @param pos The position of the element to return.
 * @return A reference to the requested element properly wrapped.
 */
[[nodiscard]] inline meta_any meta_sequence_container::operator[](const size_type pos) {
    auto it = begin();
    it.operator++(static_cast<int>(pos) - 1);
    return *it;
}

/**
 * @brief Returns false if a proxy is invalid, true otherwise.
 * @return False if the proxy is invalid, true otherwise.
 */
[[nodiscard]] inline meta_sequence_container::operator bool() const noexcept {
    return static_cast<bool>(storage);
}

/**
 * @brief Returns true if a container is also key-only, false otherwise.
 * @return True if the associative container is also key-only, false otherwise.
 */
[[nodiscard]] inline bool meta_associative_container::key_only() const noexcept {
    return key_only_container;
}

/**
 * @brief Returns the meta key type of a container.
 * @return The meta key type of the a container.
 */
[[nodiscard]] inline meta_type meta_associative_container::key_type() const noexcept {
    return key_type_node ? meta_type{*ctx, key_type_node(internal::meta_context::from(*ctx))} : meta_type{};
}

/**
 * @brief Returns the meta mapped type of a container.
 * @return The meta mapped type of the a container.
 */
[[nodiscard]] inline meta_type meta_associative_container::mapped_type() const noexcept {
    return mapped_type_node ? meta_type{*ctx, mapped_type_node(internal::meta_context::from(*ctx))} : meta_type{};
}

/*! @copydoc meta_sequence_container::value_type */
[[nodiscard]] inline meta_type meta_associative_container::value_type() const noexcept {
    return value_type_node ? meta_type{*ctx, value_type_node(internal::meta_context::from(*ctx))} : meta_type{};
}

/*! @copydoc meta_sequence_container::size */
[[nodiscard]] inline meta_associative_container::size_type meta_associative_container::size() const noexcept {
    return size_fn(storage);
}

/*! @copydoc meta_sequence_container::clear */
inline bool meta_associative_container::clear() {
    return clear_fn(storage);
}

/*! @copydoc meta_sequence_container::begin */
[[nodiscard]] inline meta_associative_container::iterator meta_associative_container::begin() {
    return iter_fn(*ctx, storage, false);
}

/*! @copydoc meta_sequence_container::end */
[[nodiscard]] inline meta_associative_container::iterator meta_associative_container::end() {
    return iter_fn(*ctx, storage, true);
}

/**
 * @brief Inserts a key only element into a container.
 * @param key The key of the element to insert.
 * @return A bool denoting whether the insertion took place.
 */
inline bool meta_associative_container::insert(meta_any key) {
    meta_any value{*ctx, std::in_place_type<void>};
    return (insert_or_erase_fn(storage, key, value) != 0u);
}

/**
 * @brief Inserts a key/value element into a container.
 * @param key The key of the element to insert.
 * @param value The value of the element to insert.
 * @return A bool denoting whether the insertion took place.
 */
inline bool meta_associative_container::insert(meta_any key, meta_any value) {
    return (insert_or_erase_fn(storage, key, value) != 0u);
}

/**
 * @brief Removes the specified element from a container.
 * @param key The key of the element to remove.
 * @return A bool denoting whether the removal took place.
 */
inline meta_associative_container::size_type meta_associative_container::erase(meta_any key) {
    return insert(std::move(key), meta_any{meta_ctx_arg, *ctx});
}

/**
 * @brief Returns an iterator to the element with a given key, if any.
 * @param key The key of the element to search.
 * @return An iterator to the element with the given key, if any.
 */
[[nodiscard]] inline meta_associative_container::iterator meta_associative_container::find(meta_any key) {
    return find_fn(*ctx, storage, key);
}

/**
 * @brief Returns false if a proxy is invalid, true otherwise.
 * @return False if the proxy is invalid, true otherwise.
 */
[[nodiscard]] inline meta_associative_container::operator bool() const noexcept {
    return static_cast<bool>(storage);
}

} // namespace entt

#endif

// #include "meta/node.hpp"
#ifndef ENTT_META_NODE_HPP
#define ENTT_META_NODE_HPP

#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../container/dense_map.hpp"

// #include "../core/attribute.h"

// #include "../core/enum.hpp"

// #include "../core/fwd.hpp"

// #include "../core/type_info.hpp"

// #include "../core/type_traits.hpp"

// #include "../core/utility.hpp"

// #include "context.hpp"

// #include "type_traits.hpp"


namespace entt {

class meta_any;
class meta_type;
struct meta_handle;

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

enum class meta_traits : std::uint32_t {
    is_none = 0x0000,
    is_const = 0x0001,
    is_static = 0x0002,
    is_arithmetic = 0x0004,
    is_integral = 0x0008,
    is_signed = 0x0010,
    is_array = 0x0020,
    is_enum = 0x0040,
    is_class = 0x0080,
    is_meta_pointer_like = 0x0100,
    is_meta_sequence_container = 0x0200,
    is_meta_associative_container = 0x0400,
    _entt_enum_as_bitmask
};

struct meta_type_node;

struct meta_prop_node {
    meta_type_node (*type)(const meta_context &) noexcept {};
    std::shared_ptr<void> value{};
};

struct meta_base_node {
    meta_type_node (*type)(const meta_context &) noexcept {};
    const void *(*cast)(const void *) noexcept {};
};

struct meta_conv_node {
    meta_any (*conv)(const meta_ctx &, const void *){};
};

struct meta_ctor_node {
    using size_type = std::size_t;

    size_type arity{0u};
    meta_type (*arg)(const meta_ctx &, const size_type) noexcept {};
    meta_any (*invoke)(const meta_ctx &, meta_any *const){};
};

struct meta_dtor_node {
    void (*dtor)(void *){};
};

struct meta_data_node {
    using size_type = std::size_t;

    meta_traits traits{meta_traits::is_none};
    size_type arity{0u};
    meta_type_node (*type)(const meta_context &) noexcept {};
    meta_type (*arg)(const meta_ctx &, const size_type) noexcept {};
    bool (*set)(meta_handle, meta_any){};
    meta_any (*get)(const meta_ctx &, meta_handle){};
    dense_map<id_type, meta_prop_node, identity> prop{};
};

struct meta_func_node {
    using size_type = std::size_t;

    meta_traits traits{meta_traits::is_none};
    size_type arity{0u};
    meta_type_node (*ret)(const meta_context &) noexcept {};
    meta_type (*arg)(const meta_ctx &, const size_type) noexcept {};
    meta_any (*invoke)(const meta_ctx &, meta_handle, meta_any *const){};
    std::shared_ptr<meta_func_node> next{};
    dense_map<id_type, meta_prop_node, identity> prop{};
};

struct meta_template_node {
    using size_type = std::size_t;

    size_type arity{0u};
    meta_type_node (*type)(const meta_context &) noexcept {};
    meta_type_node (*arg)(const meta_context &, const size_type) noexcept {};
};

struct meta_type_descriptor {
    dense_map<id_type, meta_ctor_node, identity> ctor{};
    dense_map<id_type, meta_base_node, identity> base{};
    dense_map<id_type, meta_conv_node, identity> conv{};
    dense_map<id_type, meta_data_node, identity> data{};
    dense_map<id_type, meta_func_node, identity> func{};
    dense_map<id_type, meta_prop_node, identity> prop{};
};

struct meta_type_node {
    using size_type = std::size_t;

    const type_info *info{};
    id_type id{};
    meta_traits traits{meta_traits::is_none};
    size_type size_of{0u};
    meta_type_node (*resolve)(const meta_context &) noexcept {};
    meta_type_node (*remove_pointer)(const meta_context &) noexcept {};
    meta_any (*default_constructor)(const meta_ctx &){};
    double (*conversion_helper)(void *, const void *){};
    meta_any (*from_void)(const meta_ctx &, void *, const void *){};
    meta_template_node templ{};
    meta_dtor_node dtor{};
    std::shared_ptr<meta_type_descriptor> details{};
};

template<typename Type>
meta_type_node resolve(const meta_context &) noexcept;

template<typename... Args>
[[nodiscard]] auto meta_arg_node(const meta_context &context, type_list<Args...>, [[maybe_unused]] const std::size_t index) noexcept {
    [[maybe_unused]] std::size_t pos{};
    meta_type_node (*value)(const meta_context &) noexcept = nullptr;
    ((value = (pos++ == index ? &resolve<std::remove_cv_t<std::remove_reference_t<Args>>> : value)), ...);
    ENTT_ASSERT(value != nullptr, "Out of bounds");
    return value(context);
}

[[nodiscard]] inline const void *try_cast(const meta_context &context, const meta_type_node &from, const meta_type_node &to, const void *instance) noexcept {
    if(from.info && to.info && *from.info == *to.info) {
        return instance;
    }

    if(from.details) {
        for(auto &&curr: from.details->base) {
            if(const void *elem = try_cast(context, curr.second.type(context), to, curr.second.cast(instance)); elem) {
                return elem;
            }
        }
    }

    return nullptr;
}

[[nodiscard]] inline const meta_type_node *try_resolve(const meta_context &context, const type_info &info) noexcept {
    const auto it = context.value.find(info.hash());
    return it != context.value.end() ? &it->second : nullptr;
}

template<typename Type>
[[nodiscard]] meta_type_node resolve(const meta_context &context) noexcept {
    static_assert(std::is_same_v<Type, std::remove_const_t<std::remove_reference_t<Type>>>, "Invalid type");

    if(auto *elem = try_resolve(context, type_id<Type>()); elem) {
        return *elem;
    }

    meta_type_node node{
        &type_id<Type>(),
        type_id<Type>().hash(),
        (std::is_arithmetic_v<Type> ? meta_traits::is_arithmetic : meta_traits::is_none)
            | (std::is_integral_v<Type> ? meta_traits::is_integral : meta_traits::is_none)
            | (std::is_signed_v<Type> ? meta_traits::is_signed : meta_traits::is_none)
            | (std::is_array_v<Type> ? meta_traits::is_array : meta_traits::is_none)
            | (std::is_enum_v<Type> ? meta_traits::is_enum : meta_traits::is_none)
            | (std::is_class_v<Type> ? meta_traits::is_class : meta_traits::is_none)
            | (is_meta_pointer_like_v<Type> ? meta_traits::is_meta_pointer_like : meta_traits::is_none)
            | (is_complete_v<meta_sequence_container_traits<Type>> ? meta_traits::is_meta_sequence_container : meta_traits::is_none)
            | (is_complete_v<meta_associative_container_traits<Type>> ? meta_traits::is_meta_associative_container : meta_traits::is_none),
        size_of_v<Type>,
        &resolve<Type>,
        &resolve<std::remove_cv_t<std::remove_pointer_t<Type>>>};

    if constexpr(std::is_default_constructible_v<Type>) {
        node.default_constructor = +[](const meta_ctx &ctx) {
            return meta_any{ctx, std::in_place_type<Type>};
        };
    }

    if constexpr(std::is_arithmetic_v<Type>) {
        node.conversion_helper = +[](void *bin, const void *value) {
            return bin ? static_cast<double>(*static_cast<Type *>(bin) = static_cast<Type>(*static_cast<const double *>(value))) : static_cast<double>(*static_cast<const Type *>(value));
        };
    } else if constexpr(std::is_enum_v<Type>) {
        node.conversion_helper = +[](void *bin, const void *value) {
            return bin ? static_cast<double>(*static_cast<Type *>(bin) = static_cast<Type>(static_cast<std::underlying_type_t<Type>>(*static_cast<const double *>(value)))) : static_cast<double>(*static_cast<const Type *>(value));
        };
    }

    if constexpr(!std::is_same_v<Type, void> && !std::is_function_v<Type>) {
        node.from_void = +[](const meta_ctx &ctx, void *element, const void *as_const) {
            if(element) {
                return meta_any{ctx, std::in_place_type<std::decay_t<Type> &>, *static_cast<std::decay_t<Type> *>(element)};
            }

            return meta_any{ctx, std::in_place_type<const std::decay_t<Type> &>, *static_cast<const std::decay_t<Type> *>(as_const)};
        };
    }

    if constexpr(is_complete_v<meta_template_traits<Type>>) {
        node.templ = meta_template_node{
            meta_template_traits<Type>::args_type::size,
            &resolve<typename meta_template_traits<Type>::class_type>,
            +[](const meta_context &area, const std::size_t index) noexcept { return meta_arg_node(area, typename meta_template_traits<Type>::args_type{}, index); }};
    }

    return node;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

} // namespace entt

#endif

// #include "meta/pointer.hpp"
#ifndef ENTT_META_POINTER_HPP
#define ENTT_META_POINTER_HPP

#include <memory>
#include <type_traits>
// #include "type_traits.hpp"


namespace entt {

/**
 * @brief Makes plain pointers pointer-like types for the meta system.
 * @tparam Type Element type.
 */
template<typename Type>
struct is_meta_pointer_like<Type *>
    : std::true_type {};

/**
 * @brief Partial specialization used to reject pointers to arrays.
 * @tparam Type Type of elements of the array.
 * @tparam N Number of elements of the array.
 */
template<typename Type, std::size_t N>
struct is_meta_pointer_like<Type (*)[N]>
    : std::false_type {};

/**
 * @brief Makes `std::shared_ptr`s of any type pointer-like types for the meta
 * system.
 * @tparam Type Element type.
 */
template<typename Type>
struct is_meta_pointer_like<std::shared_ptr<Type>>
    : std::true_type {};

/**
 * @brief Makes `std::unique_ptr`s of any type pointer-like types for the meta
 * system.
 * @tparam Type Element type.
 * @tparam Args Other arguments.
 */
template<typename Type, typename... Args>
struct is_meta_pointer_like<std::unique_ptr<Type, Args...>>
    : std::true_type {};

} // namespace entt

#endif

// #include "meta/policy.hpp"
#ifndef ENTT_META_POLICY_HPP
#define ENTT_META_POLICY_HPP

#include <type_traits>

namespace entt {

/*! @brief Empty class type used to request the _as ref_ policy. */
struct as_ref_t final {
    /**
     * @cond TURN_OFF_DOXYGEN
     * Internal details not to be documented.
     */
    template<typename Type>
    static constexpr bool value = std::is_reference_v<Type> && !std::is_const_v<std::remove_reference_t<Type>>;
    /**
     * Internal details not to be documented.
     * @endcond
     */
};

/*! @brief Empty class type used to request the _as cref_ policy. */
struct as_cref_t final {
    /**
     * @cond TURN_OFF_DOXYGEN
     * Internal details not to be documented.
     */
    template<typename Type>
    static constexpr bool value = std::is_reference_v<Type>;
    /**
     * Internal details not to be documented.
     * @endcond
     */
};

/*! @brief Empty class type used to request the _as-is_ policy. */
struct as_is_t final {
    /**
     * @cond TURN_OFF_DOXYGEN
     * Internal details not to be documented.
     */
    template<typename>
    static constexpr bool value = true;
    /**
     * Internal details not to be documented.
     * @endcond
     */
};

/*! @brief Empty class type used to request the _as void_ policy. */
struct as_void_t final {
    /**
     * @cond TURN_OFF_DOXYGEN
     * Internal details not to be documented.
     */
    template<typename>
    static constexpr bool value = true;
    /**
     * Internal details not to be documented.
     * @endcond
     */
};

/**
 * @brief Provides the member constant `value` to true if a type also is a meta
 * policy, false otherwise.
 * @tparam Type Type to check.
 */
template<typename Type>
struct is_meta_policy
    : std::disjunction<
          std::is_same<Type, as_ref_t>,
          std::is_same<Type, as_cref_t>,
          std::is_same<Type, as_is_t>,
          std::is_same<Type, as_void_t>> {};

/**
 * @brief Helper variable template.
 * @tparam Type Type to check.
 */
template<typename Type>
inline constexpr bool is_meta_policy_v = is_meta_policy<Type>::value;

} // namespace entt

#endif

// #include "meta/range.hpp"
#ifndef ENTT_META_RANGE_HPP
#define ENTT_META_RANGE_HPP

#include <cstddef>
#include <iterator>
#include <utility>
// #include "../core/fwd.hpp"

// #include "../core/iterator.hpp"

// #include "context.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, typename It>
struct meta_range_iterator final {
    using difference_type = std::ptrdiff_t;
    using value_type = std::pair<id_type, Type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using iterator_category = std::input_iterator_tag;

    meta_range_iterator() noexcept
        : it{},
          ctx{} {}

    meta_range_iterator(const meta_ctx &area, const It iter) noexcept
        : it{iter},
          ctx{&area} {}

    meta_range_iterator &operator++() noexcept {
        return ++it, *this;
    }

    meta_range_iterator operator++(int) noexcept {
        meta_range_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr meta_range_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr meta_range_iterator operator--(int) noexcept {
        meta_range_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr meta_range_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr meta_range_iterator operator+(const difference_type value) const noexcept {
        meta_range_iterator copy = *this;
        return (copy += value);
    }

    constexpr meta_range_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr meta_range_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].first, Type{*ctx, it[value].second}};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->first, Type{*ctx, it->second}};
    }

    template<typename... Args>
    friend constexpr std::ptrdiff_t operator-(const meta_range_iterator<Args...> &, const meta_range_iterator<Args...> &) noexcept;

    template<typename... Args>
    friend constexpr bool operator==(const meta_range_iterator<Args...> &, const meta_range_iterator<Args...> &) noexcept;

    template<typename... Args>
    friend constexpr bool operator<(const meta_range_iterator<Args...> &, const meta_range_iterator<Args...> &) noexcept;

private:
    It it;
    const meta_ctx *ctx;
};

template<typename... Args>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename... Args>
[[nodiscard]] constexpr bool operator==(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename... Args>
[[nodiscard]] constexpr bool operator!=(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename... Args>
[[nodiscard]] constexpr bool operator<(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename... Args>
[[nodiscard]] constexpr bool operator>(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return rhs < lhs;
}

template<typename... Args>
[[nodiscard]] constexpr bool operator<=(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename... Args>
[[nodiscard]] constexpr bool operator>=(const meta_range_iterator<Args...> &lhs, const meta_range_iterator<Args...> &rhs) noexcept {
    return !(lhs < rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Iterable range to use to iterate all types of meta objects.
 * @tparam Type Type of meta objects returned.
 * @tparam It Type of forward iterator.
 */
template<typename Type, typename It>
using meta_range = iterable_adaptor<internal::meta_range_iterator<Type, It>>;

} // namespace entt

#endif

// #include "meta/resolve.hpp"
#ifndef ENTT_META_RESOLVE_HPP
#define ENTT_META_RESOLVE_HPP

#include <type_traits>
// #include "../core/type_info.hpp"

// #include "../locator/locator.hpp"

// #include "context.hpp"

// #include "meta.hpp"

// #include "node.hpp"

// #include "range.hpp"


namespace entt {

/**
 * @brief Returns the meta type associated with a given type.
 * @tparam Type Type to use to search for a meta type.
 * @param ctx The context from which to search for meta types.
 * @return The meta type associated with the given type, if any.
 */
template<typename Type>
[[nodiscard]] meta_type resolve(const meta_ctx &ctx) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    return {ctx, internal::resolve<std::remove_cv_t<std::remove_reference_t<Type>>>(context)};
}

/**
 * @brief Returns the meta type associated with a given type.
 * @tparam Type Type to use to search for a meta type.
 * @return The meta type associated with the given type, if any.
 */
template<typename Type>
[[nodiscard]] meta_type resolve() noexcept {
    return resolve<Type>(locator<meta_ctx>::value_or());
}

/**
 * @brief Returns a range to use to visit all meta types.
 * @param ctx The context from which to search for meta types.
 * @return An iterable range to use to visit all meta types.
 */
[[nodiscard]] inline meta_range<meta_type, typename decltype(internal::meta_context::value)::const_iterator> resolve(const meta_ctx &ctx) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    return {{ctx, context.value.cbegin()}, {ctx, context.value.cend()}};
}

/**
 * @brief Returns a range to use to visit all meta types.
 * @return An iterable range to use to visit all meta types.
 */
[[nodiscard]] inline meta_range<meta_type, typename decltype(internal::meta_context::value)::const_iterator> resolve() noexcept {
    return resolve(locator<meta_ctx>::value_or());
}

/**
 * @brief Returns the meta type associated with a given identifier, if any.
 * @param ctx The context from which to search for meta types.
 * @param id Unique identifier.
 * @return The meta type associated with the given identifier, if any.
 */
[[nodiscard]] inline meta_type resolve(const meta_ctx &ctx, const id_type id) noexcept {
    for(auto &&curr: resolve(ctx)) {
        if(curr.second.id() == id) {
            return curr.second;
        }
    }

    return meta_type{};
}

/**
 * @brief Returns the meta type associated with a given identifier, if any.
 * @param id Unique identifier.
 * @return The meta type associated with the given identifier, if any.
 */
[[nodiscard]] inline meta_type resolve(const id_type id) noexcept {
    return resolve(locator<meta_ctx>::value_or(), id);
}

/**
 * @brief Returns the meta type associated with a given type info object.
 * @param ctx The context from which to search for meta types.
 * @param info The type info object of the requested type.
 * @return The meta type associated with the given type info object, if any.
 */
[[nodiscard]] inline meta_type resolve(const meta_ctx &ctx, const type_info &info) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    const auto *elem = internal::try_resolve(context, info);
    return elem ? meta_type{ctx, *elem} : meta_type{};
}

/**
 * @brief Returns the meta type associated with a given type info object.
 * @param info The type info object of the requested type.
 * @return The meta type associated with the given type info object, if any.
 */
[[nodiscard]] inline meta_type resolve(const type_info &info) noexcept {
    return resolve(locator<meta_ctx>::value_or(), info);
}

} // namespace entt

#endif

// #include "meta/template.hpp"
#ifndef ENTT_META_TEMPLATE_HPP
#define ENTT_META_TEMPLATE_HPP

// #include "../core/type_traits.hpp"


namespace entt {

/*! @brief Utility class to disambiguate class templates. */
template<template<typename...> class>
struct meta_class_template_tag {};

/**
 * @brief General purpose traits class for generating meta template information.
 * @tparam Clazz Type of class template.
 * @tparam Args Types of template arguments.
 */
template<template<typename...> class Clazz, typename... Args>
struct meta_template_traits<Clazz<Args...>> {
    /*! @brief Wrapped class template. */
    using class_type = meta_class_template_tag<Clazz>;
    /*! @brief List of template arguments. */
    using args_type = type_list<Args...>;
};

} // namespace entt

#endif

// #include "meta/type_traits.hpp"
#ifndef ENTT_META_TYPE_TRAITS_HPP
#define ENTT_META_TYPE_TRAITS_HPP

#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Traits class template to be specialized to enable support for meta
 * template information.
 */
template<typename>
struct meta_template_traits;

/**
 * @brief Traits class template to be specialized to enable support for meta
 * sequence containers.
 */
template<typename>
struct meta_sequence_container_traits;

/**
 * @brief Traits class template to be specialized to enable support for meta
 * associative containers.
 */
template<typename>
struct meta_associative_container_traits;

/**
 * @brief Provides the member constant `value` to true if a given type is a
 * pointer-like type from the point of view of the meta system, false otherwise.
 * @tparam Type Potentially pointer-like type.
 */
template<typename>
struct is_meta_pointer_like: std::false_type {};

/**
 * @brief Partial specialization to ensure that const pointer-like types are
 * also accepted.
 * @tparam Type Potentially pointer-like type.
 */
template<typename Type>
struct is_meta_pointer_like<const Type>: is_meta_pointer_like<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type Potentially pointer-like type.
 */
template<typename Type>
inline constexpr auto is_meta_pointer_like_v = is_meta_pointer_like<Type>::value;

} // namespace entt

#endif

// #include "meta/utility.hpp"
#ifndef ENTT_META_UTILITY_HPP
#define ENTT_META_UTILITY_HPP

#include <cstddef>
#include <functional>
#include <type_traits>
#include <utility>
// #include "../core/type_traits.hpp"

// #include "../locator/locator.hpp"

// #include "meta.hpp"

// #include "node.hpp"

// #include "policy.hpp"


namespace entt {

/**
 * @brief Meta function descriptor traits.
 * @tparam Ret Function return type.
 * @tparam Args Function arguments.
 * @tparam Static Function staticness.
 * @tparam Const Function constness.
 */
template<typename Ret, typename Args, bool Static, bool Const>
struct meta_function_descriptor_traits {
    /*! @brief Meta function return type. */
    using return_type = Ret;
    /*! @brief Meta function arguments. */
    using args_type = Args;

    /*! @brief True if the meta function is static, false otherwise. */
    static constexpr bool is_static = Static;
    /*! @brief True if the meta function is const, false otherwise. */
    static constexpr bool is_const = Const;
};

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct meta_function_descriptor;

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Ret Function return type.
 * @tparam Class Actual owner of the member function.
 * @tparam Args Function arguments.
 */
template<typename Type, typename Ret, typename Class, typename... Args>
struct meta_function_descriptor<Type, Ret (Class::*)(Args...) const>
    : meta_function_descriptor_traits<
          Ret,
          std::conditional_t<std::is_base_of_v<Class, Type>, type_list<Args...>, type_list<const Class &, Args...>>,
          !std::is_base_of_v<Class, Type>,
          true> {};

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Ret Function return type.
 * @tparam Class Actual owner of the member function.
 * @tparam Args Function arguments.
 */
template<typename Type, typename Ret, typename Class, typename... Args>
struct meta_function_descriptor<Type, Ret (Class::*)(Args...)>
    : meta_function_descriptor_traits<
          Ret,
          std::conditional_t<std::is_base_of_v<Class, Type>, type_list<Args...>, type_list<Class &, Args...>>,
          !std::is_base_of_v<Class, Type>,
          false> {};

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta data is associated.
 * @tparam Class Actual owner of the data member.
 * @tparam Ret Data member type.
 */
template<typename Type, typename Ret, typename Class>
struct meta_function_descriptor<Type, Ret Class::*>
    : meta_function_descriptor_traits<
          Ret &,
          std::conditional_t<std::is_base_of_v<Class, Type>, type_list<>, type_list<Class &>>,
          !std::is_base_of_v<Class, Type>,
          false> {};

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Ret Function return type.
 * @tparam MaybeType First function argument.
 * @tparam Args Other function arguments.
 */
template<typename Type, typename Ret, typename MaybeType, typename... Args>
struct meta_function_descriptor<Type, Ret (*)(MaybeType, Args...)>
    : meta_function_descriptor_traits<
          Ret,
          std::conditional_t<std::is_base_of_v<std::remove_cv_t<std::remove_reference_t<MaybeType>>, Type>, type_list<Args...>, type_list<MaybeType, Args...>>,
          !std::is_base_of_v<std::remove_cv_t<std::remove_reference_t<MaybeType>>, Type>,
          std::is_base_of_v<std::remove_cv_t<std::remove_reference_t<MaybeType>>, Type> && std::is_const_v<std::remove_reference_t<MaybeType>>> {};

/**
 * @brief Meta function descriptor.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Ret Function return type.
 */
template<typename Type, typename Ret>
struct meta_function_descriptor<Type, Ret (*)()>
    : meta_function_descriptor_traits<
          Ret,
          type_list<>,
          true,
          false> {};

/**
 * @brief Meta function helper.
 *
 * Converts a function type to be associated with a reflected type into its meta
 * function descriptor.
 *
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Candidate The actual function to associate with the reflected type.
 */
template<typename Type, typename Candidate>
class meta_function_helper {
    template<typename Ret, typename... Args, typename Class>
    static constexpr meta_function_descriptor<Type, Ret (Class::*)(Args...) const> get_rid_of_noexcept(Ret (Class::*)(Args...) const);

    template<typename Ret, typename... Args, typename Class>
    static constexpr meta_function_descriptor<Type, Ret (Class::*)(Args...)> get_rid_of_noexcept(Ret (Class::*)(Args...));

    template<typename Ret, typename Class>
    static constexpr meta_function_descriptor<Type, Ret Class::*> get_rid_of_noexcept(Ret Class::*);

    template<typename Ret, typename... Args>
    static constexpr meta_function_descriptor<Type, Ret (*)(Args...)> get_rid_of_noexcept(Ret (*)(Args...));

    template<typename Class>
    static constexpr meta_function_descriptor<Class, decltype(&Class::operator())> get_rid_of_noexcept(Class);

public:
    /*! @brief The meta function descriptor of the given function. */
    using type = decltype(get_rid_of_noexcept(std::declval<Candidate>()));
};

/**
 * @brief Helper type.
 * @tparam Type Reflected type to which the meta function is associated.
 * @tparam Candidate The actual function to associate with the reflected type.
 */
template<typename Type, typename Candidate>
using meta_function_helper_t = typename meta_function_helper<Type, Candidate>::type;

/**
 * @brief Wraps a value depending on the given policy.
 *
 * This function always returns a wrapped value in the requested context.<br/>
 * Therefore, if the passed value is itself a wrapped object with a different
 * context, it undergoes a rebinding to the requested context.
 *
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Type Type of value to wrap.
 * @param ctx The context from which to search for meta types.
 * @param value Value to wrap.
 * @return A meta any containing the returned value, if any.
 */
template<typename Policy = as_is_t, typename Type>
std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_dispatch(const meta_ctx &ctx, [[maybe_unused]] Type &&value) {
    if constexpr(std::is_same_v<Policy, as_void_t>) {
        return meta_any{ctx, std::in_place_type<void>};
    } else if constexpr(std::is_same_v<Policy, as_ref_t>) {
        return meta_any{ctx, std::in_place_type<Type>, value};
    } else if constexpr(std::is_same_v<Policy, as_cref_t>) {
        static_assert(std::is_lvalue_reference_v<Type>, "Invalid type");
        return meta_any{ctx, std::in_place_type<const std::remove_reference_t<Type> &>, std::as_const(value)};
    } else {
        return meta_any{ctx, std::forward<Type>(value)};
    }
}

/**
 * @brief Wraps a value depending on the given policy.
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Type Type of value to wrap.
 * @param value Value to wrap.
 * @return A meta any containing the returned value, if any.
 */
template<typename Policy = as_is_t, typename Type>
std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_dispatch(Type &&value) {
    return meta_dispatch<Policy, Type>(locator<meta_ctx>::value_or(), std::forward<Type>(value));
}

/**
 * @brief Returns the meta type of the i-th element of a list of arguments.
 * @tparam Type Type list of the actual types of arguments.
 * @param ctx The context from which to search for meta types.
 * @param index The index of the element for which to return the meta type.
 * @return The meta type of the i-th element of the list of arguments.
 */
template<typename Type>
[[nodiscard]] static meta_type meta_arg(const meta_ctx &ctx, const std::size_t index) noexcept {
    auto &&context = internal::meta_context::from(ctx);
    return {ctx, internal::meta_arg_node(context, Type{}, index)};
}

/**
 * @brief Returns the meta type of the i-th element of a list of arguments.
 * @tparam Type Type list of the actual types of arguments.
 * @param index The index of the element for which to return the meta type.
 * @return The meta type of the i-th element of the list of arguments.
 */
template<typename Type>
[[nodiscard]] static meta_type meta_arg(const std::size_t index) noexcept {
    return meta_arg<Type>(locator<meta_ctx>::value_or(), index);
}

/**
 * @brief Sets the value of a given variable.
 * @tparam Type Reflected type to which the variable is associated.
 * @tparam Data The actual variable to set.
 * @param instance An opaque instance of the underlying type, if required.
 * @param value Parameter to use to set the variable.
 * @return True in case of success, false otherwise.
 */
template<typename Type, auto Data>
[[nodiscard]] bool meta_setter([[maybe_unused]] meta_handle instance, [[maybe_unused]] meta_any value) {
    if constexpr(!std::is_same_v<decltype(Data), Type> && !std::is_same_v<decltype(Data), std::nullptr_t>) {
        if constexpr(std::is_member_function_pointer_v<decltype(Data)> || std::is_function_v<std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>>) {
            using descriptor = meta_function_helper_t<Type, decltype(Data)>;
            using data_type = type_list_element_t<descriptor::is_static, typename descriptor::args_type>;

            if(auto *const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
                std::invoke(Data, *clazz, value.cast<data_type>());
                return true;
            }
        } else if constexpr(std::is_member_object_pointer_v<decltype(Data)>) {
            using data_type = std::remove_reference_t<typename meta_function_helper_t<Type, decltype(Data)>::return_type>;

            if constexpr(!std::is_array_v<data_type> && !std::is_const_v<data_type>) {
                if(auto *const clazz = instance->try_cast<Type>(); clazz && value.allow_cast<data_type>()) {
                    std::invoke(Data, *clazz) = value.cast<data_type>();
                    return true;
                }
            }
        } else {
            using data_type = std::remove_reference_t<decltype(*Data)>;

            if constexpr(!std::is_array_v<data_type> && !std::is_const_v<data_type>) {
                if(value.allow_cast<data_type>()) {
                    *Data = value.cast<data_type>();
                    return true;
                }
            }
        }
    }

    return false;
}

/**
 * @brief Gets the value of a given variable.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the variable is associated.
 * @tparam Data The actual variable to get.
 * @tparam Policy Optional policy (no policy set by default).
 * @param ctx The context from which to search for meta types.
 * @param instance An opaque instance of the underlying type, if required.
 * @return A meta any containing the value of the underlying variable.
 */
template<typename Type, auto Data, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_getter(const meta_ctx &ctx, [[maybe_unused]] meta_handle instance) {
    if constexpr(std::is_member_pointer_v<decltype(Data)> || std::is_function_v<std::remove_reference_t<std::remove_pointer_t<decltype(Data)>>>) {
        if constexpr(!std::is_array_v<std::remove_cv_t<std::remove_reference_t<std::invoke_result_t<decltype(Data), Type &>>>>) {
            if constexpr(std::is_invocable_v<decltype(Data), Type &>) {
                if(auto *clazz = instance->try_cast<Type>(); clazz) {
                    return meta_dispatch<Policy>(ctx, std::invoke(Data, *clazz));
                }
            }

            if constexpr(std::is_invocable_v<decltype(Data), const Type &>) {
                if(auto *fallback = instance->try_cast<const Type>(); fallback) {
                    return meta_dispatch<Policy>(ctx, std::invoke(Data, *fallback));
                }
            }
        }

        return meta_any{meta_ctx_arg, ctx};
    } else if constexpr(std::is_pointer_v<decltype(Data)>) {
        if constexpr(std::is_array_v<std::remove_pointer_t<decltype(Data)>>) {
            return meta_any{meta_ctx_arg, ctx};
        } else {
            return meta_dispatch<Policy>(ctx, *Data);
        }
    } else {
        return meta_dispatch<Policy>(ctx, Data);
    }
}

/**
 * @brief Gets the value of a given variable.
 * @tparam Type Reflected type to which the variable is associated.
 * @tparam Data The actual variable to get.
 * @tparam Policy Optional policy (no policy set by default).
 * @param instance An opaque instance of the underlying type, if required.
 * @return A meta any containing the value of the underlying variable.
 */
template<typename Type, auto Data, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_getter(meta_handle instance) {
    return meta_getter<Type, Data, Policy>(locator<meta_ctx>::value_or(), std::move(instance));
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Policy, typename Candidate, typename... Args>
[[nodiscard]] meta_any meta_invoke_with_args(const meta_ctx &ctx, Candidate &&candidate, Args &&...args) {
    if constexpr(std::is_same_v<decltype(std::invoke(std::forward<Candidate>(candidate), args...)), void>) {
        std::invoke(std::forward<Candidate>(candidate), args...);
        return meta_any{ctx, std::in_place_type<void>};
    } else {
        return meta_dispatch<Policy>(ctx, std::invoke(std::forward<Candidate>(candidate), args...));
    }
}

template<typename Type, typename Policy, typename Candidate, std::size_t... Index>
[[nodiscard]] meta_any meta_invoke(const meta_ctx &ctx, [[maybe_unused]] meta_handle instance, Candidate &&candidate, [[maybe_unused]] meta_any *args, std::index_sequence<Index...>) {
    using descriptor = meta_function_helper_t<Type, std::remove_reference_t<Candidate>>;

    if constexpr(std::is_invocable_v<std::remove_reference_t<Candidate>, const Type &, type_list_element_t<Index, typename descriptor::args_type>...>) {
        if(const auto *const clazz = instance->try_cast<const Type>(); clazz && ((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
            return meta_invoke_with_args<Policy>(ctx, std::forward<Candidate>(candidate), *clazz, (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
        }
    } else if constexpr(std::is_invocable_v<std::remove_reference_t<Candidate>, Type &, type_list_element_t<Index, typename descriptor::args_type>...>) {
        if(auto *const clazz = instance->try_cast<Type>(); clazz && ((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
            return meta_invoke_with_args<Policy>(ctx, std::forward<Candidate>(candidate), *clazz, (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
        }
    } else {
        if(((args + Index)->allow_cast<type_list_element_t<Index, typename descriptor::args_type>>() && ...)) {
            return meta_invoke_with_args<Policy>(ctx, std::forward<Candidate>(candidate), (args + Index)->cast<type_list_element_t<Index, typename descriptor::args_type>>()...);
        }
    }

    return meta_any{meta_ctx_arg, ctx};
}

template<typename Type, typename... Args, std::size_t... Index>
[[nodiscard]] meta_any meta_construct(const meta_ctx &ctx, meta_any *const args, std::index_sequence<Index...>) {
    if(((args + Index)->allow_cast<Args>() && ...)) {
        return meta_any{ctx, std::in_place_type<Type>, (args + Index)->cast<Args>()...};
    }

    return meta_any{meta_ctx_arg, ctx};
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Tries to _invoke_ an object given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the object to _invoke_ is associated.
 * @tparam Policy Optional policy (no policy set by default).
 * @param ctx The context from which to search for meta types.
 * @tparam Candidate The type of the actual object to _invoke_.
 * @param instance An opaque instance of the underlying type, if required.
 * @param candidate The actual object to _invoke_.
 * @param args Parameters to use to _invoke_ the object.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, typename Policy = as_is_t, typename Candidate>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_invoke(const meta_ctx &ctx, meta_handle instance, Candidate &&candidate, meta_any *const args) {
    return internal::meta_invoke<Type, Policy>(ctx, std::move(instance), std::forward<Candidate>(candidate), args, std::make_index_sequence<meta_function_helper_t<Type, std::remove_reference_t<Candidate>>::args_type::size>{});
}

/**
 * @brief Tries to _invoke_ an object given a list of erased parameters.
 * @tparam Type Reflected type to which the object to _invoke_ is associated.
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Candidate The type of the actual object to _invoke_.
 * @param instance An opaque instance of the underlying type, if required.
 * @param candidate The actual object to _invoke_.
 * @param args Parameters to use to _invoke_ the object.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, typename Policy = as_is_t, typename Candidate>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_invoke(meta_handle instance, Candidate &&candidate, meta_any *const args) {
    return meta_invoke<Type, Policy>(locator<meta_ctx>::value_or(), std::move(instance), std::forward<Candidate>(candidate), args);
}

/**
 * @brief Tries to invoke a function given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the function is associated.
 * @tparam Candidate The actual function to invoke.
 * @tparam Policy Optional policy (no policy set by default).
 * @param ctx The context from which to search for meta types.
 * @param instance An opaque instance of the underlying type, if required.
 * @param args Parameters to use to invoke the function.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, auto Candidate, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_invoke(const meta_ctx &ctx, meta_handle instance, meta_any *const args) {
    return internal::meta_invoke<Type, Policy>(ctx, std::move(instance), Candidate, args, std::make_index_sequence<meta_function_helper_t<Type, std::remove_reference_t<decltype(Candidate)>>::args_type::size>{});
}

/**
 * @brief Tries to invoke a function given a list of erased parameters.
 * @tparam Type Reflected type to which the function is associated.
 * @tparam Candidate The actual function to invoke.
 * @tparam Policy Optional policy (no policy set by default).
 * @param instance An opaque instance of the underlying type, if required.
 * @param args Parameters to use to invoke the function.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, auto Candidate, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_invoke(meta_handle instance, meta_any *const args) {
    return meta_invoke<Type, Candidate, Policy>(locator<meta_ctx>::value_or(), std::move(instance), args);
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Actual type of the instance to construct.
 * @tparam Args Types of arguments expected.
 * @param ctx The context from which to search for meta types.
 * @param args Parameters to use to construct the instance.
 * @return A meta any containing the new instance, if any.
 */
template<typename Type, typename... Args>
[[nodiscard]] meta_any meta_construct(const meta_ctx &ctx, meta_any *const args) {
    return internal::meta_construct<Type, Args...>(ctx, args, std::index_sequence_for<Args...>{});
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 * @tparam Type Actual type of the instance to construct.
 * @tparam Args Types of arguments expected.
 * @param args Parameters to use to construct the instance.
 * @return A meta any containing the new instance, if any.
 */
template<typename Type, typename... Args>
[[nodiscard]] meta_any meta_construct(meta_any *const args) {
    return meta_construct<Type, Args...>(locator<meta_ctx>::value_or(), args);
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the object to _invoke_ is associated.
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Candidate The type of the actual object to _invoke_.
 * @param ctx The context from which to search for meta types.
 * @param candidate The actual object to _invoke_.
 * @param args Parameters to use to _invoke_ the object.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, typename Policy = as_is_t, typename Candidate>
[[nodiscard]] meta_any meta_construct(const meta_ctx &ctx, Candidate &&candidate, meta_any *const args) {
    if constexpr(meta_function_helper_t<Type, Candidate>::is_static || std::is_class_v<std::remove_cv_t<std::remove_reference_t<Candidate>>>) {
        return internal::meta_invoke<Type, Policy>(ctx, {}, std::forward<Candidate>(candidate), args, std::make_index_sequence<meta_function_helper_t<Type, std::remove_reference_t<Candidate>>::args_type::size>{});
    } else {
        return internal::meta_invoke<Type, Policy>(ctx, *args, std::forward<Candidate>(candidate), args + 1u, std::make_index_sequence<meta_function_helper_t<Type, std::remove_reference_t<Candidate>>::args_type::size>{});
    }
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 * @tparam Type Reflected type to which the object to _invoke_ is associated.
 * @tparam Policy Optional policy (no policy set by default).
 * @tparam Candidate The type of the actual object to _invoke_.
 * @param candidate The actual object to _invoke_.
 * @param args Parameters to use to _invoke_ the object.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, typename Policy = as_is_t, typename Candidate>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_construct(Candidate &&candidate, meta_any *const args) {
    return meta_construct<Type, Policy>(locator<meta_ctx>::value_or(), std::forward<Candidate>(candidate), args);
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 *
 * @warning
 * The context provided is used only for the return type.<br/>
 * It's up to the caller to bind the arguments to the right context(s).
 *
 * @tparam Type Reflected type to which the function is associated.
 * @tparam Candidate The actual function to invoke.
 * @tparam Policy Optional policy (no policy set by default).
 * @param ctx The context from which to search for meta types.
 * @param args Parameters to use to invoke the function.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, auto Candidate, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_construct(const meta_ctx &ctx, meta_any *const args) {
    return meta_construct<Type, Policy>(ctx, Candidate, args);
}

/**
 * @brief Tries to construct an instance given a list of erased parameters.
 * @tparam Type Reflected type to which the function is associated.
 * @tparam Candidate The actual function to invoke.
 * @tparam Policy Optional policy (no policy set by default).
 * @param args Parameters to use to invoke the function.
 * @return A meta any containing the returned value, if any.
 */
template<typename Type, auto Candidate, typename Policy = as_is_t>
[[nodiscard]] std::enable_if_t<is_meta_policy_v<Policy>, meta_any> meta_construct(meta_any *const args) {
    return meta_construct<Type, Candidate, Policy>(locator<meta_ctx>::value_or(), args);
}

} // namespace entt

#endif

// #include "platform/android-ndk-r17.hpp"
#ifndef ENTT_PLATFORM_ANDROID_NDK_R17_HPP
#define ENTT_PLATFORM_ANDROID_NDK_R17_HPP

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

#ifdef __ANDROID__
#    include <android/ndk-version.h>
#    if __NDK_MAJOR__ == 17

#        include <functional>
#        include <type_traits>
#        include <utility>

namespace std {

namespace internal {

template<typename Func, typename... Args>
constexpr auto is_invocable(int) -> decltype(std::invoke(std::declval<Func>(), std::declval<Args>()...), std::true_type{});

template<typename, typename...>
constexpr std::false_type is_invocable(...);

template<typename Ret, typename Func, typename... Args>
constexpr auto is_invocable_r(int)
-> std::enable_if_t<decltype(std::is_convertible_v<decltype(std::invoke(std::declval<Func>(), std::declval<Args>()...)), Ret>, std::true_type>;


template<typename, typename, typename...>
constexpr std::false_type is_invocable_r(...);

} // namespace internal

template<typename Func, typename... Args>
struct is_invocable: decltype(internal::is_invocable<Func, Args...>(0)) {};

template<typename Func, typename... Argsv>
inline constexpr bool is_invocable_v = std::is_invocable<Func, Args...>::value;

template<typename Ret, typename Func, typename... Args>
struct is_invocable_r: decltype(internal::is_invocable_r<Ret, Func, Args...>(0)) {};

template<typename Ret, typename Func, typename... Args>
inline constexpr bool is_invocable_r_v = std::is_invocable_r<Ret, Func, Args...>::value;

template<typename Func, typename... Args>
struct invoke_result {
    using type = decltype(std::invoke(std::declval<Func>(), std::declval<Args>()...));
};

template<typename Func, typename... Args>
using invoke_result_t = typename std::invoke_result<Func, Args...>::type;

} // namespace std

#    endif
#endif

/**
 * Internal details not to be documented.
 * @endcond
 */

#endif

// #include "poly/poly.hpp"
#ifndef ENTT_POLY_POLY_HPP
#define ENTT_POLY_POLY_HPP

#include <cstddef>
#include <functional>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../core/any.hpp"
#ifndef ENTT_CORE_ANY_HPP
#define ENTT_CORE_ANY_HPP

#include <cstddef>
#include <memory>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif

// #include "type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"
#ifndef ENTT_CORE_ATTRIBUTE_H
#define ENTT_CORE_ATTRIBUTE_H

#ifndef ENTT_EXPORT
#    if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
#        define ENTT_EXPORT __declspec(dllexport)
#        define ENTT_IMPORT __declspec(dllimport)
#        define ENTT_HIDDEN
#    elif defined __GNUC__ && __GNUC__ >= 4
#        define ENTT_EXPORT __attribute__((visibility("default")))
#        define ENTT_IMPORT __attribute__((visibility("default")))
#        define ENTT_HIDDEN __attribute__((visibility("hidden")))
#    else /* Unsupported compiler */
#        define ENTT_EXPORT
#        define ENTT_IMPORT
#        define ENTT_HIDDEN
#    endif
#endif

#ifndef ENTT_API
#    if defined ENTT_API_EXPORT
#        define ENTT_API ENTT_EXPORT
#    elif defined ENTT_API_IMPORT
#        define ENTT_API ENTT_IMPORT
#    else /* No API */
#        define ENTT_API
#    endif
#endif

#endif

// #include "fwd.hpp"

// #include "hashed_string.hpp"
#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP

#include <cstddef>
#include <cstdint>
// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename>
struct fnv1a_traits;

template<>
struct fnv1a_traits<std::uint32_t> {
    using type = std::uint32_t;
    static constexpr std::uint32_t offset = 2166136261;
    static constexpr std::uint32_t prime = 16777619;
};

template<>
struct fnv1a_traits<std::uint64_t> {
    using type = std::uint64_t;
    static constexpr std::uint64_t offset = 14695981039346656037ull;
    static constexpr std::uint64_t prime = 1099511628211ull;
};

template<typename Char>
struct basic_hashed_string {
    using value_type = Char;
    using size_type = std::size_t;
    using hash_type = id_type;

    const value_type *repr;
    size_type length;
    hash_type hash;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Zero overhead unique identifier.
 *
 * A hashed string is a compile-time tool that allows users to use
 * human-readable identifiers in the codebase while using their numeric
 * counterparts at runtime.<br/>
 * Because of that, a hashed string can also be used in constant expressions if
 * required.
 *
 * @warning
 * This class doesn't take ownership of user-supplied strings nor does it make a
 * copy of them.
 *
 * @tparam Char Character type.
 */
template<typename Char>
class basic_hashed_string: internal::basic_hashed_string<Char> {
    using base_type = internal::basic_hashed_string<Char>;
    using hs_traits = internal::fnv1a_traits<id_type>;

    struct const_wrapper {
        // non-explicit constructor on purpose
        constexpr const_wrapper(const Char *str) noexcept
            : repr{str} {}

        const Char *repr;
    };

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str) noexcept {
        base_type base{str, 0u, hs_traits::offset};

        for(; str[base.length]; ++base.length) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[base.length])) * hs_traits::prime;
        }

        return base;
    }

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str, const std::size_t len) noexcept {
        base_type base{str, len, hs_traits::offset};

        for(size_type pos{}; pos < len; ++pos) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[pos])) * hs_traits::prime;
        }

        return base;
    }

public:
    /*! @brief Character type. */
    using value_type = typename base_type::value_type;
    /*! @brief Unsigned integer type. */
    using size_type = typename base_type::size_type;
    /*! @brief Unsigned integer type. */
    using hash_type = typename base_type::hash_type;

    /**
     * @brief Returns directly the numeric representation of a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const value_type *str, const size_type len) noexcept {
        return basic_hashed_string{str, len};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     * @return The numeric representation of the string.
     */
    template<std::size_t N>
    [[nodiscard]] static constexpr hash_type value(const value_type (&str)[N]) noexcept {
        return basic_hashed_string{str};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @param wrapper Helps achieving the purpose by relying on overloading.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const_wrapper wrapper) noexcept {
        return basic_hashed_string{wrapper};
    }

    /*! @brief Constructs an empty hashed string. */
    constexpr basic_hashed_string() noexcept
        : base_type{} {}

    /**
     * @brief Constructs a hashed string from a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     */
    constexpr basic_hashed_string(const value_type *str, const size_type len) noexcept
        : base_type{helper(str, len)} {}

    /**
     * @brief Constructs a hashed string from an array of const characters.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     */
    template<std::size_t N>
    constexpr basic_hashed_string(const value_type (&str)[N]) noexcept
        : base_type{helper(str)} {}

    /**
     * @brief Explicit constructor on purpose to avoid constructing a hashed
     * string directly from a `const value_type *`.
     *
     * @warning
     * The lifetime of the string is not extended nor is it copied.
     *
     * @param wrapper Helps achieving the purpose by relying on overloading.
     */
    explicit constexpr basic_hashed_string(const_wrapper wrapper) noexcept
        : base_type{helper(wrapper.repr)} {}

    /**
     * @brief Returns the size a hashed string.
     * @return The size of the hashed string.
     */
    [[nodiscard]] constexpr size_type size() const noexcept {
        return base_type::length;
    }

    /**
     * @brief Returns the human-readable representation of a hashed string.
     * @return The string used to initialize the hashed string.
     */
    [[nodiscard]] constexpr const value_type *data() const noexcept {
        return base_type::repr;
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr hash_type value() const noexcept {
        return base_type::hash;
    }

    /*! @copydoc data */
    [[nodiscard]] constexpr operator const value_type *() const noexcept {
        return data();
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr operator hash_type() const noexcept {
        return value();
    }
};

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @param str Human-readable identifier.
 * @param len Length of the string to hash.
 */
template<typename Char>
basic_hashed_string(const Char *str, const std::size_t len) -> basic_hashed_string<Char>;

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @tparam N Number of characters of the identifier.
 * @param str Human-readable identifier.
 */
template<typename Char, std::size_t N>
basic_hashed_string(const Char (&str)[N]) -> basic_hashed_string<Char>;

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings are identical, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator==(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() == rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings differ, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than the second, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() < rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs < rhs);
}

/*! @brief Aliases for common character types. */
using hashed_string = basic_hashed_string<char>;

/*! @brief Aliases for common character types. */
using hashed_wstring = basic_hashed_string<wchar_t>;

inline namespace literals {

/**
 * @brief User defined literal for hashed strings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed string.
 */
[[nodiscard]] constexpr hashed_string operator"" _hs(const char *str, std::size_t) noexcept {
    return hashed_string{str};
}

/**
 * @brief User defined literal for hashed wstrings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed wstring.
 */
[[nodiscard]] constexpr hashed_wstring operator"" _hws(const wchar_t *str, std::size_t) noexcept {
    return hashed_wstring{str};
}

} // namespace literals

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

enum class any_operation : std::uint8_t {
    copy,
    move,
    transfer,
    assign,
    destroy,
    compare,
    get
};

enum class any_policy : std::uint8_t {
    owner,
    ref,
    cref
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A SBO friendly, type-safe container for single values of any type.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 */
template<std::size_t Len, std::size_t Align>
class basic_any {
    using operation = internal::any_operation;
    using policy = internal::any_policy;
    using vtable_type = const void *(const operation, const basic_any &, const void *);

    struct storage_type {
        alignas(Align) std::byte data[Len + !Len];
    };

    template<typename Type>
    static constexpr bool in_situ = Len && alignof(Type) <= Align && sizeof(Type) <= Len &&std::is_nothrow_move_constructible_v<Type>;

    template<typename Type>
    static const void *basic_vtable(const operation op, const basic_any &value, const void *other) {
        static_assert(!std::is_same_v<Type, void> && std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, Type>, "Invalid type");
        const Type *element = nullptr;

        if constexpr(in_situ<Type>) {
            element = value.owner() ? reinterpret_cast<const Type *>(&value.storage) : static_cast<const Type *>(value.instance);
        } else {
            element = static_cast<const Type *>(value.instance);
        }

        switch(op) {
        case operation::copy:
            if constexpr(std::is_copy_constructible_v<Type>) {
                static_cast<basic_any *>(const_cast<void *>(other))->initialize<Type>(*element);
            }
            break;
        case operation::move:
            if constexpr(in_situ<Type>) {
                if(value.owner()) {
                    return new(&static_cast<basic_any *>(const_cast<void *>(other))->storage) Type{std::move(*const_cast<Type *>(element))};
                }
            }

            return (static_cast<basic_any *>(const_cast<void *>(other))->instance = std::exchange(const_cast<basic_any &>(value).instance, nullptr));
        case operation::transfer:
            if constexpr(std::is_move_assignable_v<Type>) {
                *const_cast<Type *>(element) = std::move(*static_cast<Type *>(const_cast<void *>(other)));
                return other;
            }
            [[fallthrough]];
        case operation::assign:
            if constexpr(std::is_copy_assignable_v<Type>) {
                *const_cast<Type *>(element) = *static_cast<const Type *>(other);
                return other;
            }
            break;
        case operation::destroy:
            if constexpr(in_situ<Type>) {
                element->~Type();
            } else if constexpr(std::is_array_v<Type>) {
                delete[] element;
            } else {
                delete element;
            }
            break;
        case operation::compare:
            if constexpr(!std::is_function_v<Type> && !std::is_array_v<Type> && is_equality_comparable_v<Type>) {
                return *element == *static_cast<const Type *>(other) ? other : nullptr;
            } else {
                return (element == other) ? other : nullptr;
            }
        case operation::get:
            return element;
        }

        return nullptr;
    }

    template<typename Type, typename... Args>
    void initialize([[maybe_unused]] Args &&...args) {
        info = &type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();

        if constexpr(!std::is_void_v<Type>) {
            vtable = basic_vtable<std::remove_cv_t<std::remove_reference_t<Type>>>;

            if constexpr(std::is_lvalue_reference_v<Type>) {
                static_assert(sizeof...(Args) == 1u && (std::is_lvalue_reference_v<Args> && ...), "Invalid arguments");
                mode = std::is_const_v<std::remove_reference_t<Type>> ? policy::cref : policy::ref;
                instance = (std::addressof(args), ...);
            } else if constexpr(in_situ<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                if constexpr(sizeof...(Args) != 0u && std::is_aggregate_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                    new(&storage) std::remove_cv_t<std::remove_reference_t<Type>>{std::forward<Args>(args)...};
                } else {
                    new(&storage) std::remove_cv_t<std::remove_reference_t<Type>>(std::forward<Args>(args)...);
                }
            } else {
                if constexpr(sizeof...(Args) != 0u && std::is_aggregate_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
                    instance = new std::remove_cv_t<std::remove_reference_t<Type>>{std::forward<Args>(args)...};
                } else {
                    instance = new std::remove_cv_t<std::remove_reference_t<Type>>(std::forward<Args>(args)...);
                }
            }
        }
    }

    basic_any(const basic_any &other, const policy pol) noexcept
        : instance{other.data()},
          info{other.info},
          vtable{other.vtable},
          mode{pol} {}

public:
    /*! @brief Size of the internal storage. */
    static constexpr auto length = Len;
    /*! @brief Alignment requirement. */
    static constexpr auto alignment = Align;

    /*! @brief Default constructor. */
    constexpr basic_any() noexcept
        : basic_any{std::in_place_type<void>} {}

    /**
     * @brief Constructs a wrapper by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit basic_any(std::in_place_type_t<Type>, Args &&...args)
        : instance{},
          info{},
          vtable{},
          mode{policy::owner} {
        initialize<Type>(std::forward<Args>(args)...);
    }

    /**
     * @brief Constructs a wrapper from a given value.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>>>
    basic_any(Type &&value)
        : basic_any{std::in_place_type<std::decay_t<Type>>, std::forward<Type>(value)} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    basic_any(const basic_any &other)
        : basic_any{} {
        if(other.vtable) {
            other.vtable(operation::copy, other, this);
        }
    }

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_any(basic_any &&other) noexcept
        : instance{},
          info{other.info},
          vtable{other.vtable},
          mode{other.mode} {
        if(other.vtable) {
            other.vtable(operation::move, other, this);
        }
    }

    /*! @brief Frees the internal storage, whatever it means. */
    ~basic_any() {
        if(vtable && owner()) {
            vtable(operation::destroy, *this, nullptr);
        }
    }

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This any object.
     */
    basic_any &operator=(const basic_any &other) {
        reset();

        if(other.vtable) {
            other.vtable(operation::copy, other, this);
        }

        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This any object.
     */
    basic_any &operator=(basic_any &&other) noexcept {
        reset();

        if(other.vtable) {
            other.vtable(operation::move, other, this);
            info = other.info;
            vtable = other.vtable;
            mode = other.mode;
        }

        return *this;
    }

    /**
     * @brief Value assignment operator.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @param value An instance of an object to use to initialize the wrapper.
     * @return This any object.
     */
    template<typename Type>
    std::enable_if_t<!std::is_same_v<std::decay_t<Type>, basic_any>, basic_any &>
    operator=(Type &&value) {
        emplace<std::decay_t<Type>>(std::forward<Type>(value));
        return *this;
    }

    /**
     * @brief Returns the object type if any, `type_id<void>()` otherwise.
     * @return The object type if any, `type_id<void>()` otherwise.
     */
    [[nodiscard]] const type_info &type() const noexcept {
        return *info;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data() const noexcept {
        return vtable ? vtable(operation::get, *this, nullptr) : nullptr;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @param req Expected type.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data(const type_info &req) const noexcept {
        return *info == req ? data() : nullptr;
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] void *data() noexcept {
        return mode == policy::cref ? nullptr : const_cast<void *>(std::as_const(*this).data());
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @param req Expected type.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] void *data(const type_info &req) noexcept {
        return mode == policy::cref ? nullptr : const_cast<void *>(std::as_const(*this).data(req));
    }

    /**
     * @brief Replaces the contained object by creating a new instance directly.
     * @tparam Type Type of object to use to initialize the wrapper.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    void emplace(Args &&...args) {
        reset();
        initialize<Type>(std::forward<Args>(args)...);
    }

    /**
     * @brief Assigns a value to the contained object without replacing it.
     * @param other The value to assign to the contained object.
     * @return True in case of success, false otherwise.
     */
    bool assign(const basic_any &other) {
        if(vtable && mode != policy::cref && *info == *other.info) {
            return (vtable(operation::assign, *this, other.data()) != nullptr);
        }

        return false;
    }

    /*! @copydoc assign */
    bool assign(basic_any &&other) {
        if(vtable && mode != policy::cref && *info == *other.info) {
            if(auto *val = other.data(); val) {
                return (vtable(operation::transfer, *this, val) != nullptr);
            } else {
                return (vtable(operation::assign, *this, std::as_const(other).data()) != nullptr);
            }
        }

        return false;
    }

    /*! @brief Destroys contained object */
    void reset() {
        if(vtable && owner()) {
            vtable(operation::destroy, *this, nullptr);
        }

        // unnecessary but it helps to detect nasty bugs
        ENTT_ASSERT((instance = nullptr) == nullptr, "");
        info = &type_id<void>();
        vtable = nullptr;
        mode = policy::owner;
    }

    /**
     * @brief Returns false if a wrapper is empty, true otherwise.
     * @return False if the wrapper is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return vtable != nullptr;
    }

    /**
     * @brief Checks if two wrappers differ in their content.
     * @param other Wrapper with which to compare.
     * @return False if the two objects differ in their content, true otherwise.
     */
    [[nodiscard]] bool operator==(const basic_any &other) const noexcept {
        if(vtable && *info == *other.info) {
            return (vtable(operation::compare, *this, other.data()) != nullptr);
        }

        return (!vtable && !other.vtable);
    }

    /**
     * @brief Checks if two wrappers differ in their content.
     * @param other Wrapper with which to compare.
     * @return True if the two objects differ in their content, false otherwise.
     */
    [[nodiscard]] bool operator!=(const basic_any &other) const noexcept {
        return !(*this == other);
    }

    /**
     * @brief Aliasing constructor.
     * @return A wrapper that shares a reference to an unmanaged object.
     */
    [[nodiscard]] basic_any as_ref() noexcept {
        return basic_any{*this, (mode == policy::cref ? policy::cref : policy::ref)};
    }

    /*! @copydoc as_ref */
    [[nodiscard]] basic_any as_ref() const noexcept {
        return basic_any{*this, policy::cref};
    }

    /**
     * @brief Returns true if a wrapper owns its object, false otherwise.
     * @return True if the wrapper owns its object, false otherwise.
     */
    [[nodiscard]] bool owner() const noexcept {
        return (mode == policy::owner);
    }

private:
    union {
        const void *instance;
        storage_type storage;
    };
    const type_info *info;
    vtable_type *vtable;
    policy mode;
};

/**
 * @brief Performs type-safe access to the contained object.
 * @tparam Type Type to which conversion is required.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Alignment requirement.
 * @param data Target any object.
 * @return The element converted to the requested type.
 */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(const basic_any<Len, Align> &data) noexcept {
    const auto *const instance = any_cast<std::remove_reference_t<Type>>(&data);
    ENTT_ASSERT(instance, "Invalid instance");
    return static_cast<Type>(*instance);
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(basic_any<Len, Align> &data) noexcept {
    // forces const on non-reference types to make them work also with wrappers for const references
    auto *const instance = any_cast<std::remove_reference_t<const Type>>(&data);
    ENTT_ASSERT(instance, "Invalid instance");
    return static_cast<Type>(*instance);
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type any_cast(basic_any<Len, Align> &&data) noexcept {
    if constexpr(std::is_copy_constructible_v<std::remove_cv_t<std::remove_reference_t<Type>>>) {
        if(auto *const instance = any_cast<std::remove_reference_t<Type>>(&data); instance) {
            return static_cast<Type>(std::move(*instance));
        } else {
            return any_cast<Type>(data);
        }
    } else {
        auto *const instance = any_cast<std::remove_reference_t<Type>>(&data);
        ENTT_ASSERT(instance, "Invalid instance");
        return static_cast<Type>(std::move(*instance));
    }
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
const Type *any_cast(const basic_any<Len, Align> *data) noexcept {
    const auto &info = type_id<std::remove_cv_t<Type>>();
    return static_cast<const Type *>(data->data(info));
}

/*! @copydoc any_cast */
template<typename Type, std::size_t Len, std::size_t Align>
Type *any_cast(basic_any<Len, Align> *data) noexcept {
    if constexpr(std::is_const_v<Type>) {
        // last attempt to make wrappers for const references return their values
        return any_cast<Type>(&std::as_const(*data));
    } else {
        const auto &info = type_id<std::remove_cv_t<Type>>();
        return static_cast<Type *>(data->data(info));
    }
}

/**
 * @brief Constructs a wrapper from a given type, passing it all arguments.
 * @tparam Type Type of object to use to initialize the wrapper.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 * @tparam Args Types of arguments to use to construct the new instance.
 * @param args Parameters to use to construct the instance.
 * @return A properly initialized wrapper for an object of the given type.
 */
template<typename Type, std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename... Args>
basic_any<Len, Align> make_any(Args &&...args) {
    return basic_any<Len, Align>{std::in_place_type<Type>, std::forward<Args>(args)...};
}

/**
 * @brief Forwards its argument and avoids copies for lvalue references.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 * @tparam Type Type of argument to use to construct the new instance.
 * @param value Parameter to use to construct the instance.
 * @return A properly initialized and not necessarily owning wrapper.
 */
template<std::size_t Len = basic_any<>::length, std::size_t Align = basic_any<Len>::alignment, typename Type>
basic_any<Len, Align> forward_as_any(Type &&value) {
    return basic_any<Len, Align>{std::in_place_type<Type &&>, std::forward<Type>(value)};
}

} // namespace entt

#endif

// #include "../core/type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"

// #include "fwd.hpp"

// #include "hashed_string.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_POLY_FWD_HPP
#define ENTT_POLY_FWD_HPP

#include <cstddef>

namespace entt {

template<typename, std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_poly;

/**
 * @brief Alias declaration for the most common use case.
 * @tparam Concept Concept descriptor.
 */
template<typename Concept>
using poly = basic_poly<Concept>;

} // namespace entt

#endif


namespace entt {

/*! @brief Inspector class used to infer the type of the virtual table. */
struct poly_inspector {
    /**
     * @brief Generic conversion operator (definition only).
     * @tparam Type Type to which conversion is requested.
     */
    template<class Type>
    operator Type &&() const;

    /**
     * @brief Dummy invocation function (definition only).
     * @tparam Member Index of the function to invoke.
     * @tparam Args Types of arguments to pass to the function.
     * @param args The arguments to pass to the function.
     * @return A poly inspector convertible to any type.
     */
    template<std::size_t Member, typename... Args>
    poly_inspector invoke(Args &&...args) const;

    /*! @copydoc invoke */
    template<std::size_t Member, typename... Args>
    poly_inspector invoke(Args &&...args);
};

/**
 * @brief Static virtual table factory.
 * @tparam Concept Concept descriptor.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Alignment requirement.
 */
template<typename Concept, std::size_t Len, std::size_t Align>
class poly_vtable {
    using inspector = typename Concept::template type<poly_inspector>;

    template<typename Ret, typename... Args>
    static auto vtable_entry(Ret (*)(inspector &, Args...)) -> Ret (*)(basic_any<Len, Align> &, Args...);

    template<typename Ret, typename... Args>
    static auto vtable_entry(Ret (*)(const inspector &, Args...)) -> Ret (*)(const basic_any<Len, Align> &, Args...);

    template<typename Ret, typename... Args>
    static auto vtable_entry(Ret (*)(Args...)) -> Ret (*)(const basic_any<Len, Align> &, Args...);

    template<typename Ret, typename... Args>
    static auto vtable_entry(Ret (inspector::*)(Args...)) -> Ret (*)(basic_any<Len, Align> &, Args...);

    template<typename Ret, typename... Args>
    static auto vtable_entry(Ret (inspector::*)(Args...) const) -> Ret (*)(const basic_any<Len, Align> &, Args...);

    template<auto... Candidate>
    static auto make_vtable(value_list<Candidate...>) noexcept
        -> decltype(std::make_tuple(vtable_entry(Candidate)...));

    template<typename... Func>
    [[nodiscard]] static constexpr auto make_vtable(type_list<Func...>) noexcept {
        if constexpr(sizeof...(Func) == 0u) {
            return decltype(make_vtable(typename Concept::template impl<inspector>{})){};
        } else if constexpr((std::is_function_v<Func> && ...)) {
            return decltype(std::make_tuple(vtable_entry(std::declval<Func inspector::*>())...)){};
        }
    }

    template<typename Type, auto Candidate, typename Ret, typename Any, typename... Args>
    static void fill_vtable_entry(Ret (*&entry)(Any &, Args...)) noexcept {
        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
            entry = +[](Any &, Args... args) -> Ret {
                return std::invoke(Candidate, std::forward<Args>(args)...);
            };
        } else {
            entry = +[](Any &instance, Args... args) -> Ret {
                return static_cast<Ret>(std::invoke(Candidate, any_cast<constness_as_t<Type, Any> &>(instance), std::forward<Args>(args)...));
            };
        }
    }

    template<typename Type, auto... Index>
    [[nodiscard]] static auto fill_vtable(std::index_sequence<Index...>) noexcept {
        vtable_type impl{};
        (fill_vtable_entry<Type, value_list_element_v<Index, typename Concept::template impl<Type>>>(std::get<Index>(impl)), ...);
        return impl;
    }

    using vtable_type = decltype(make_vtable(Concept{}));
    static constexpr bool is_mono_v = std::tuple_size_v<vtable_type> == 1u;

public:
    /*! @brief Virtual table type. */
    using type = std::conditional_t<is_mono_v, std::tuple_element_t<0u, vtable_type>, const vtable_type *>;

    /**
     * @brief Returns a static virtual table for a specific concept and type.
     * @tparam Type The type for which to generate the virtual table.
     * @return A static virtual table for the given concept and type.
     */
    template<typename Type>
    [[nodiscard]] static type instance() noexcept {
        static_assert(std::is_same_v<Type, std::decay_t<Type>>, "Type differs from its decayed form");
        static const vtable_type vtable = fill_vtable<Type>(std::make_index_sequence<Concept::template impl<Type>::size>{});

        if constexpr(is_mono_v) {
            return std::get<0>(vtable);
        } else {
            return &vtable;
        }
    }
};

/**
 * @brief Poly base class used to inject functionalities into concepts.
 * @tparam Poly The outermost poly class.
 */
template<typename Poly>
struct poly_base {
    /**
     * @brief Invokes a function from the static virtual table.
     * @tparam Member Index of the function to invoke.
     * @tparam Args Types of arguments to pass to the function.
     * @param self A reference to the poly object that made the call.
     * @param args The arguments to pass to the function.
     * @return The return value of the invoked function, if any.
     */
    template<std::size_t Member, typename... Args>
    [[nodiscard]] decltype(auto) invoke(const poly_base &self, Args &&...args) const {
        const auto &poly = static_cast<const Poly &>(self);

        if constexpr(std::is_function_v<std::remove_pointer_t<decltype(poly.vtable)>>) {
            return poly.vtable(poly.storage, std::forward<Args>(args)...);
        } else {
            return std::get<Member>(*poly.vtable)(poly.storage, std::forward<Args>(args)...);
        }
    }

    /*! @copydoc invoke */
    template<std::size_t Member, typename... Args>
    [[nodiscard]] decltype(auto) invoke(poly_base &self, Args &&...args) {
        auto &poly = static_cast<Poly &>(self);

        if constexpr(std::is_function_v<std::remove_pointer_t<decltype(poly.vtable)>>) {
            static_assert(Member == 0u, "Unknown member");
            return poly.vtable(poly.storage, std::forward<Args>(args)...);
        } else {
            return std::get<Member>(*poly.vtable)(poly.storage, std::forward<Args>(args)...);
        }
    }
};

/**
 * @brief Shortcut for calling `poly_base<Type>::invoke`.
 * @tparam Member Index of the function to invoke.
 * @tparam Poly A fully defined poly object.
 * @tparam Args Types of arguments to pass to the function.
 * @param self A reference to the poly object that made the call.
 * @param args The arguments to pass to the function.
 * @return The return value of the invoked function, if any.
 */
template<std::size_t Member, typename Poly, typename... Args>
decltype(auto) poly_call(Poly &&self, Args &&...args) {
    return std::forward<Poly>(self).template invoke<Member>(self, std::forward<Args>(args)...);
}

/**
 * @brief Static polymorphism made simple and within everyone's reach.
 *
 * Static polymorphism is a very powerful tool in C++, albeit sometimes
 * cumbersome to obtain.<br/>
 * This class aims to make it simple and easy to use.
 *
 * @note
 * Both deduced and defined static virtual tables are supported.<br/>
 * Moreover, the `poly` class template also works with unmanaged objects.
 *
 * @tparam Concept Concept descriptor.
 * @tparam Len Size of the storage reserved for the small buffer optimization.
 * @tparam Align Optional alignment requirement.
 */
template<typename Concept, std::size_t Len, std::size_t Align>
class basic_poly: private Concept::template type<poly_base<basic_poly<Concept, Len, Align>>> {
    /*! @brief A poly base is allowed to snoop into a poly object. */
    friend struct poly_base<basic_poly>;

public:
    /*! @brief Concept type. */
    using concept_type = typename Concept::template type<poly_base<basic_poly>>;
    /*! @brief Virtual table type. */
    using vtable_type = typename poly_vtable<Concept, Len, Align>::type;

    /*! @brief Default constructor. */
    basic_poly() noexcept
        : storage{},
          vtable{} {}

    /**
     * @brief Constructs a poly by directly initializing the new object.
     * @tparam Type Type of object to use to initialize the poly.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    explicit basic_poly(std::in_place_type_t<Type>, Args &&...args)
        : storage{std::in_place_type<Type>, std::forward<Args>(args)...},
          vtable{poly_vtable<Concept, Len, Align>::template instance<std::remove_cv_t<std::remove_reference_t<Type>>>()} {}

    /**
     * @brief Constructs a poly from a given value.
     * @tparam Type Type of object to use to initialize the poly.
     * @param value An instance of an object to use to initialize the poly.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Type>>, basic_poly>>>
    basic_poly(Type &&value) noexcept
        : basic_poly{std::in_place_type<std::remove_cv_t<std::remove_reference_t<Type>>>, std::forward<Type>(value)} {}

    /**
     * @brief Returns the object type if any, `type_id<void>()` otherwise.
     * @return The object type if any, `type_id<void>()` otherwise.
     */
    [[nodiscard]] const type_info &type() const noexcept {
        return storage.type();
    }

    /**
     * @brief Returns an opaque pointer to the contained instance.
     * @return An opaque pointer the contained instance, if any.
     */
    [[nodiscard]] const void *data() const noexcept {
        return storage.data();
    }

    /*! @copydoc data */
    [[nodiscard]] void *data() noexcept {
        return storage.data();
    }

    /**
     * @brief Replaces the contained object by creating a new instance directly.
     * @tparam Type Type of object to use to initialize the poly.
     * @tparam Args Types of arguments to use to construct the new instance.
     * @param args Parameters to use to construct the instance.
     */
    template<typename Type, typename... Args>
    void emplace(Args &&...args) {
        storage.template emplace<Type>(std::forward<Args>(args)...);
        vtable = poly_vtable<Concept, Len, Align>::template instance<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }

    /*! @brief Destroys contained object */
    void reset() {
        storage.reset();
        vtable = {};
    }

    /**
     * @brief Returns false if a poly is empty, true otherwise.
     * @return False if the poly is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(storage);
    }

    /**
     * @brief Returns a pointer to the underlying concept.
     * @return A pointer to the underlying concept.
     */
    [[nodiscard]] concept_type *operator->() noexcept {
        return this;
    }

    /*! @copydoc operator-> */
    [[nodiscard]] const concept_type *operator->() const noexcept {
        return this;
    }

    /**
     * @brief Aliasing constructor.
     * @return A poly that shares a reference to an unmanaged object.
     */
    [[nodiscard]] basic_poly as_ref() noexcept {
        basic_poly ref{};
        ref.storage = storage.as_ref();
        ref.vtable = vtable;
        return ref;
    }

    /*! @copydoc as_ref */
    [[nodiscard]] basic_poly as_ref() const noexcept {
        basic_poly ref{};
        ref.storage = storage.as_ref();
        ref.vtable = vtable;
        return ref;
    }

private:
    basic_any<Len, Align> storage;
    vtable_type vtable;
};

} // namespace entt

#endif

// #include "process/process.hpp"
#ifndef ENTT_PROCESS_PROCESS_HPP
#define ENTT_PROCESS_PROCESS_HPP

#include <cstdint>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Base class for processes.
 *
 * This class stays true to the CRTP idiom. Derived classes must specify what's
 * the intended type for elapsed times.<br/>
 * A process should expose publicly the following member functions whether
 * required:
 *
 * * @code{.cpp}
 *   void update(Delta, void *);
 *   @endcode
 *
 *   It's invoked once per tick until a process is explicitly aborted or it
 *   terminates either with or without errors. Even though it's not mandatory to
 *   declare this member function, as a rule of thumb each process should at
 *   least define it to work properly. The `void *` parameter is an opaque
 *   pointer to user data (if any) forwarded directly to the process during an
 *   update.
 *
 * * @code{.cpp}
 *   void init();
 *   @endcode
 *
 *   It's invoked when the process joins the running queue of a scheduler. This
 *   happens as soon as it's attached to the scheduler if the process is a top
 *   level one, otherwise when it replaces its parent if the process is a
 *   continuation.
 *
 * * @code{.cpp}
 *   void succeeded();
 *   @endcode
 *
 *   It's invoked in case of success, immediately after an update and during the
 *   same tick.
 *
 * * @code{.cpp}
 *   void failed();
 *   @endcode
 *
 *   It's invoked in case of errors, immediately after an update and during the
 *   same tick.
 *
 * * @code{.cpp}
 *   void aborted();
 *   @endcode
 *
 *   It's invoked only if a process is explicitly aborted. There is no guarantee
 *   that it executes in the same tick, this depends solely on whether the
 *   process is aborted immediately or not.
 *
 * Derived classes can change the internal state of a process by invoking the
 * `succeed` and `fail` protected member functions and even pause or unpause the
 * process itself.
 *
 * @sa scheduler
 *
 * @tparam Derived Actual type of process that extends the class template.
 * @tparam Delta Type to use to provide elapsed time.
 */
template<typename Derived, typename Delta>
class process {
    enum class state : std::uint8_t {
        uninitialized = 0,
        running,
        paused,
        succeeded,
        failed,
        aborted,
        finished,
        rejected
    };

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::uninitialized>)
        -> decltype(std::declval<Target>().init(), void()) {
        static_cast<Target *>(this)->init();
    }

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::running>, Delta delta, void *data)
        -> decltype(std::declval<Target>().update(delta, data), void()) {
        static_cast<Target *>(this)->update(delta, data);
    }

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::succeeded>)
        -> decltype(std::declval<Target>().succeeded(), void()) {
        static_cast<Target *>(this)->succeeded();
    }

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::failed>)
        -> decltype(std::declval<Target>().failed(), void()) {
        static_cast<Target *>(this)->failed();
    }

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::aborted>)
        -> decltype(std::declval<Target>().aborted(), void()) {
        static_cast<Target *>(this)->aborted();
    }

    void next(...) const noexcept {}

protected:
    /**
     * @brief Terminates a process with success if it's still alive.
     *
     * The function is idempotent and it does nothing if the process isn't
     * alive.
     */
    void succeed() noexcept {
        if(alive()) {
            current = state::succeeded;
        }
    }

    /**
     * @brief Terminates a process with errors if it's still alive.
     *
     * The function is idempotent and it does nothing if the process isn't
     * alive.
     */
    void fail() noexcept {
        if(alive()) {
            current = state::failed;
        }
    }

    /**
     * @brief Stops a process if it's in a running state.
     *
     * The function is idempotent and it does nothing if the process isn't
     * running.
     */
    void pause() noexcept {
        if(current == state::running) {
            current = state::paused;
        }
    }

    /**
     * @brief Restarts a process if it's paused.
     *
     * The function is idempotent and it does nothing if the process isn't
     * paused.
     */
    void unpause() noexcept {
        if(current == state::paused) {
            current = state::running;
        }
    }

public:
    /*! @brief Type used to provide elapsed time. */
    using delta_type = Delta;

    /*! @brief Default destructor. */
    virtual ~process() noexcept {
        static_assert(std::is_base_of_v<process, Derived>, "Incorrect use of the class template");
    }

    /**
     * @brief Aborts a process if it's still alive.
     *
     * The function is idempotent and it does nothing if the process isn't
     * alive.
     *
     * @param immediately Requests an immediate operation.
     */
    void abort(const bool immediately = false) {
        if(alive()) {
            current = state::aborted;

            if(immediately) {
                tick({});
            }
        }
    }

    /**
     * @brief Returns true if a process is either running or paused.
     * @return True if the process is still alive, false otherwise.
     */
    [[nodiscard]] bool alive() const noexcept {
        return current == state::running || current == state::paused;
    }

    /**
     * @brief Returns true if a process is already terminated.
     * @return True if the process is terminated, false otherwise.
     */
    [[nodiscard]] bool finished() const noexcept {
        return current == state::finished;
    }

    /**
     * @brief Returns true if a process is currently paused.
     * @return True if the process is paused, false otherwise.
     */
    [[nodiscard]] bool paused() const noexcept {
        return current == state::paused;
    }

    /**
     * @brief Returns true if a process terminated with errors.
     * @return True if the process terminated with errors, false otherwise.
     */
    [[nodiscard]] bool rejected() const noexcept {
        return current == state::rejected;
    }

    /**
     * @brief Updates a process and its internal state if required.
     * @param delta Elapsed time.
     * @param data Optional data.
     */
    void tick(const Delta delta, void *data = nullptr) {
        switch(current) {
        case state::uninitialized:
            next(std::integral_constant<state, state::uninitialized>{});
            current = state::running;
            break;
        case state::running:
            next(std::integral_constant<state, state::running>{}, delta, data);
            break;
        default:
            // suppress warnings
            break;
        }

        // if it's dead, it must be notified and removed immediately
        switch(current) {
        case state::succeeded:
            next(std::integral_constant<state, state::succeeded>{});
            current = state::finished;
            break;
        case state::failed:
            next(std::integral_constant<state, state::failed>{});
            current = state::rejected;
            break;
        case state::aborted:
            next(std::integral_constant<state, state::aborted>{});
            current = state::rejected;
            break;
        default:
            // suppress warnings
            break;
        }
    }

private:
    state current{state::uninitialized};
};

/**
 * @brief Adaptor for lambdas and functors to turn them into processes.
 *
 * Lambdas and functors can't be used directly with a scheduler for they are not
 * properly defined processes with managed life cycles.<br/>
 * This class helps in filling the gap and turning lambdas and functors into
 * full featured processes usable by a scheduler.
 *
 * The signature of the function call operator should be equivalent to the
 * following:
 *
 * @code{.cpp}
 * void(Delta delta, void *data, auto succeed, auto fail);
 * @endcode
 *
 * Where:
 *
 * * `delta` is the elapsed time.
 * * `data` is an opaque pointer to user data if any, `nullptr` otherwise.
 * * `succeed` is a function to call when a process terminates with success.
 * * `fail` is a function to call when a process terminates with errors.
 *
 * The signature of the function call operator of both `succeed` and `fail`
 * is equivalent to the following:
 *
 * @code{.cpp}
 * void();
 * @endcode
 *
 * Usually users shouldn't worry about creating adaptors. A scheduler will
 * create them internally each and avery time a lambda or a functor is used as
 * a process.
 *
 * @sa process
 * @sa scheduler
 *
 * @tparam Func Actual type of process.
 * @tparam Delta Type to use to provide elapsed time.
 */
template<typename Func, typename Delta>
struct process_adaptor: process<process_adaptor<Func, Delta>, Delta>, private Func {
    /**
     * @brief Constructs a process adaptor from a lambda or a functor.
     * @tparam Args Types of arguments to use to initialize the actual process.
     * @param args Parameters to use to initialize the actual process.
     */
    template<typename... Args>
    process_adaptor(Args &&...args)
        : Func{std::forward<Args>(args)...} {}

    /**
     * @brief Updates a process and its internal state if required.
     * @param delta Elapsed time.
     * @param data Optional data.
     */
    void update(const Delta delta, void *data) {
        Func::operator()(
            delta,
            data,
            [this]() { this->succeed(); },
            [this]() { this->fail(); });
    }
};

} // namespace entt

#endif

// #include "process/scheduler.hpp"
#ifndef ENTT_PROCESS_SCHEDULER_HPP
#define ENTT_PROCESS_SCHEDULER_HPP

#include <algorithm>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "process.hpp"
#ifndef ENTT_PROCESS_PROCESS_HPP
#define ENTT_PROCESS_PROCESS_HPP

#include <cstdint>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Base class for processes.
 *
 * This class stays true to the CRTP idiom. Derived classes must specify what's
 * the intended type for elapsed times.<br/>
 * A process should expose publicly the following member functions whether
 * required:
 *
 * * @code{.cpp}
 *   void update(Delta, void *);
 *   @endcode
 *
 *   It's invoked once per tick until a process is explicitly aborted or it
 *   terminates either with or without errors. Even though it's not mandatory to
 *   declare this member function, as a rule of thumb each process should at
 *   least define it to work properly. The `void *` parameter is an opaque
 *   pointer to user data (if any) forwarded directly to the process during an
 *   update.
 *
 * * @code{.cpp}
 *   void init();
 *   @endcode
 *
 *   It's invoked when the process joins the running queue of a scheduler. This
 *   happens as soon as it's attached to the scheduler if the process is a top
 *   level one, otherwise when it replaces its parent if the process is a
 *   continuation.
 *
 * * @code{.cpp}
 *   void succeeded();
 *   @endcode
 *
 *   It's invoked in case of success, immediately after an update and during the
 *   same tick.
 *
 * * @code{.cpp}
 *   void failed();
 *   @endcode
 *
 *   It's invoked in case of errors, immediately after an update and during the
 *   same tick.
 *
 * * @code{.cpp}
 *   void aborted();
 *   @endcode
 *
 *   It's invoked only if a process is explicitly aborted. There is no guarantee
 *   that it executes in the same tick, this depends solely on whether the
 *   process is aborted immediately or not.
 *
 * Derived classes can change the internal state of a process by invoking the
 * `succeed` and `fail` protected member functions and even pause or unpause the
 * process itself.
 *
 * @sa scheduler
 *
 * @tparam Derived Actual type of process that extends the class template.
 * @tparam Delta Type to use to provide elapsed time.
 */
template<typename Derived, typename Delta>
class process {
    enum class state : std::uint8_t {
        uninitialized = 0,
        running,
        paused,
        succeeded,
        failed,
        aborted,
        finished,
        rejected
    };

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::uninitialized>)
        -> decltype(std::declval<Target>().init(), void()) {
        static_cast<Target *>(this)->init();
    }

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::running>, Delta delta, void *data)
        -> decltype(std::declval<Target>().update(delta, data), void()) {
        static_cast<Target *>(this)->update(delta, data);
    }

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::succeeded>)
        -> decltype(std::declval<Target>().succeeded(), void()) {
        static_cast<Target *>(this)->succeeded();
    }

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::failed>)
        -> decltype(std::declval<Target>().failed(), void()) {
        static_cast<Target *>(this)->failed();
    }

    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::aborted>)
        -> decltype(std::declval<Target>().aborted(), void()) {
        static_cast<Target *>(this)->aborted();
    }

    void next(...) const noexcept {}

protected:
    /**
     * @brief Terminates a process with success if it's still alive.
     *
     * The function is idempotent and it does nothing if the process isn't
     * alive.
     */
    void succeed() noexcept {
        if(alive()) {
            current = state::succeeded;
        }
    }

    /**
     * @brief Terminates a process with errors if it's still alive.
     *
     * The function is idempotent and it does nothing if the process isn't
     * alive.
     */
    void fail() noexcept {
        if(alive()) {
            current = state::failed;
        }
    }

    /**
     * @brief Stops a process if it's in a running state.
     *
     * The function is idempotent and it does nothing if the process isn't
     * running.
     */
    void pause() noexcept {
        if(current == state::running) {
            current = state::paused;
        }
    }

    /**
     * @brief Restarts a process if it's paused.
     *
     * The function is idempotent and it does nothing if the process isn't
     * paused.
     */
    void unpause() noexcept {
        if(current == state::paused) {
            current = state::running;
        }
    }

public:
    /*! @brief Type used to provide elapsed time. */
    using delta_type = Delta;

    /*! @brief Default destructor. */
    virtual ~process() noexcept {
        static_assert(std::is_base_of_v<process, Derived>, "Incorrect use of the class template");
    }

    /**
     * @brief Aborts a process if it's still alive.
     *
     * The function is idempotent and it does nothing if the process isn't
     * alive.
     *
     * @param immediately Requests an immediate operation.
     */
    void abort(const bool immediately = false) {
        if(alive()) {
            current = state::aborted;

            if(immediately) {
                tick({});
            }
        }
    }

    /**
     * @brief Returns true if a process is either running or paused.
     * @return True if the process is still alive, false otherwise.
     */
    [[nodiscard]] bool alive() const noexcept {
        return current == state::running || current == state::paused;
    }

    /**
     * @brief Returns true if a process is already terminated.
     * @return True if the process is terminated, false otherwise.
     */
    [[nodiscard]] bool finished() const noexcept {
        return current == state::finished;
    }

    /**
     * @brief Returns true if a process is currently paused.
     * @return True if the process is paused, false otherwise.
     */
    [[nodiscard]] bool paused() const noexcept {
        return current == state::paused;
    }

    /**
     * @brief Returns true if a process terminated with errors.
     * @return True if the process terminated with errors, false otherwise.
     */
    [[nodiscard]] bool rejected() const noexcept {
        return current == state::rejected;
    }

    /**
     * @brief Updates a process and its internal state if required.
     * @param delta Elapsed time.
     * @param data Optional data.
     */
    void tick(const Delta delta, void *data = nullptr) {
        switch(current) {
        case state::uninitialized:
            next(std::integral_constant<state, state::uninitialized>{});
            current = state::running;
            break;
        case state::running:
            next(std::integral_constant<state, state::running>{}, delta, data);
            break;
        default:
            // suppress warnings
            break;
        }

        // if it's dead, it must be notified and removed immediately
        switch(current) {
        case state::succeeded:
            next(std::integral_constant<state, state::succeeded>{});
            current = state::finished;
            break;
        case state::failed:
            next(std::integral_constant<state, state::failed>{});
            current = state::rejected;
            break;
        case state::aborted:
            next(std::integral_constant<state, state::aborted>{});
            current = state::rejected;
            break;
        default:
            // suppress warnings
            break;
        }
    }

private:
    state current{state::uninitialized};
};

/**
 * @brief Adaptor for lambdas and functors to turn them into processes.
 *
 * Lambdas and functors can't be used directly with a scheduler for they are not
 * properly defined processes with managed life cycles.<br/>
 * This class helps in filling the gap and turning lambdas and functors into
 * full featured processes usable by a scheduler.
 *
 * The signature of the function call operator should be equivalent to the
 * following:
 *
 * @code{.cpp}
 * void(Delta delta, void *data, auto succeed, auto fail);
 * @endcode
 *
 * Where:
 *
 * * `delta` is the elapsed time.
 * * `data` is an opaque pointer to user data if any, `nullptr` otherwise.
 * * `succeed` is a function to call when a process terminates with success.
 * * `fail` is a function to call when a process terminates with errors.
 *
 * The signature of the function call operator of both `succeed` and `fail`
 * is equivalent to the following:
 *
 * @code{.cpp}
 * void();
 * @endcode
 *
 * Usually users shouldn't worry about creating adaptors. A scheduler will
 * create them internally each and avery time a lambda or a functor is used as
 * a process.
 *
 * @sa process
 * @sa scheduler
 *
 * @tparam Func Actual type of process.
 * @tparam Delta Type to use to provide elapsed time.
 */
template<typename Func, typename Delta>
struct process_adaptor: process<process_adaptor<Func, Delta>, Delta>, private Func {
    /**
     * @brief Constructs a process adaptor from a lambda or a functor.
     * @tparam Args Types of arguments to use to initialize the actual process.
     * @param args Parameters to use to initialize the actual process.
     */
    template<typename... Args>
    process_adaptor(Args &&...args)
        : Func{std::forward<Args>(args)...} {}

    /**
     * @brief Updates a process and its internal state if required.
     * @param delta Elapsed time.
     * @param data Optional data.
     */
    void update(const Delta delta, void *data) {
        Func::operator()(
            delta,
            data,
            [this]() { this->succeed(); },
            [this]() { this->fail(); });
    }
};

} // namespace entt

#endif


namespace entt {

/**
 * @brief Cooperative scheduler for processes.
 *
 * A cooperative scheduler runs processes and helps managing their life cycles.
 *
 * Each process is invoked once per tick. If a process terminates, it's
 * removed automatically from the scheduler and it's never invoked again.<br/>
 * A process can also have a child. In this case, the process is replaced with
 * its child when it terminates if it returns with success. In case of errors,
 * both the process and its child are discarded.
 *
 * Example of use (pseudocode):
 *
 * @code{.cpp}
 * scheduler.attach([](auto delta, void *, auto succeed, auto fail) {
 *     // code
 * }).then<my_process>(arguments...);
 * @endcode
 *
 * In order to invoke all scheduled processes, call the `update` member function
 * passing it the elapsed time to forward to the tasks.
 *
 * @sa process
 *
 * @tparam Delta Type to use to provide elapsed time.
 */
template<typename Delta>
class scheduler {
    struct process_handler {
        using instance_type = std::unique_ptr<void, void (*)(void *)>;
        using update_fn_type = bool(scheduler &, std::size_t, Delta, void *);
        using abort_fn_type = void(scheduler &, std::size_t, bool);
        using next_type = std::unique_ptr<process_handler>;

        instance_type instance;
        update_fn_type *update;
        abort_fn_type *abort;
        next_type next;
    };

    struct continuation {
        continuation(process_handler *ref) noexcept
            : handler{ref} {}

        template<typename Proc, typename... Args>
        continuation then(Args &&...args) {
            static_assert(std::is_base_of_v<process<Proc, Delta>, Proc>, "Invalid process type");
            auto proc = typename process_handler::instance_type{new Proc{std::forward<Args>(args)...}, &scheduler::deleter<Proc>};
            handler->next.reset(new process_handler{std::move(proc), &scheduler::update<Proc>, &scheduler::abort<Proc>, nullptr});
            handler = handler->next.get();
            return *this;
        }

        template<typename Func>
        continuation then(Func &&func) {
            return then<process_adaptor<std::decay_t<Func>, Delta>>(std::forward<Func>(func));
        }

    private:
        process_handler *handler;
    };

    template<typename Proc>
    [[nodiscard]] static bool update(scheduler &owner, std::size_t pos, const Delta delta, void *data) {
        auto *process = static_cast<Proc *>(owner.handlers[pos].instance.get());
        process->tick(delta, data);

        if(process->rejected()) {
            return true;
        } else if(process->finished()) {
            if(auto &&handler = owner.handlers[pos]; handler.next) {
                handler = std::move(*handler.next);
                // forces the process to exit the uninitialized state
                return handler.update(owner, pos, {}, nullptr);
            }

            return true;
        }

        return false;
    }

    template<typename Proc>
    static void abort(scheduler &owner, std::size_t pos, const bool immediately) {
        static_cast<Proc *>(owner.handlers[pos].instance.get())->abort(immediately);
    }

    template<typename Proc>
    static void deleter(void *proc) {
        delete static_cast<Proc *>(proc);
    }

public:
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;

    /*! @brief Default constructor. */
    scheduler()
        : handlers{} {}

    /*! @brief Default move constructor. */
    scheduler(scheduler &&) = default;

    /*! @brief Default move assignment operator. @return This scheduler. */
    scheduler &operator=(scheduler &&) = default;

    /**
     * @brief Number of processes currently scheduled.
     * @return Number of processes currently scheduled.
     */
    [[nodiscard]] size_type size() const noexcept {
        return handlers.size();
    }

    /**
     * @brief Returns true if at least a process is currently scheduled.
     * @return True if there are scheduled processes, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return handlers.empty();
    }

    /**
     * @brief Discards all scheduled processes.
     *
     * Processes aren't aborted. They are discarded along with their children
     * and never executed again.
     */
    void clear() {
        handlers.clear();
    }

    /**
     * @brief Schedules a process for the next tick.
     *
     * Returned value is an opaque object that can be used to attach a child to
     * the given process. The child is automatically scheduled when the process
     * terminates and only if the process returns with success.
     *
     * Example of use (pseudocode):
     *
     * @code{.cpp}
     * // schedules a task in the form of a process class
     * scheduler.attach<my_process>(arguments...)
     * // appends a child in the form of a lambda function
     * .then([](auto delta, void *, auto succeed, auto fail) {
     *     // code
     * })
     * // appends a child in the form of another process class
     * .then<my_other_process>();
     * @endcode
     *
     * @tparam Proc Type of process to schedule.
     * @tparam Args Types of arguments to use to initialize the process.
     * @param args Parameters to use to initialize the process.
     * @return An opaque object to use to concatenate processes.
     */
    template<typename Proc, typename... Args>
    auto attach(Args &&...args) {
        static_assert(std::is_base_of_v<process<Proc, Delta>, Proc>, "Invalid process type");
        auto proc = typename process_handler::instance_type{new Proc{std::forward<Args>(args)...}, &scheduler::deleter<Proc>};
        auto &&ref = handlers.emplace_back(process_handler{std::move(proc), &scheduler::update<Proc>, &scheduler::abort<Proc>, nullptr});
        // forces the process to exit the uninitialized state
        ref.update(*this, handlers.size() - 1u, {}, nullptr);
        return continuation{&handlers.back()};
    }

    /**
     * @brief Schedules a process for the next tick.
     *
     * A process can be either a lambda or a functor. The scheduler wraps both
     * of them in a process adaptor internally.<br/>
     * The signature of the function call operator should be equivalent to the
     * following:
     *
     * @code{.cpp}
     * void(Delta delta, void *data, auto succeed, auto fail);
     * @endcode
     *
     * Where:
     *
     * * `delta` is the elapsed time.
     * * `data` is an opaque pointer to user data if any, `nullptr` otherwise.
     * * `succeed` is a function to call when a process terminates with success.
     * * `fail` is a function to call when a process terminates with errors.
     *
     * The signature of the function call operator of both `succeed` and `fail`
     * is equivalent to the following:
     *
     * @code{.cpp}
     * void();
     * @endcode
     *
     * Returned value is an opaque object that can be used to attach a child to
     * the given process. The child is automatically scheduled when the process
     * terminates and only if the process returns with success.
     *
     * Example of use (pseudocode):
     *
     * @code{.cpp}
     * // schedules a task in the form of a lambda function
     * scheduler.attach([](auto delta, void *, auto succeed, auto fail) {
     *     // code
     * })
     * // appends a child in the form of another lambda function
     * .then([](auto delta, void *, auto succeed, auto fail) {
     *     // code
     * })
     * // appends a child in the form of a process class
     * .then<my_process>(arguments...);
     * @endcode
     *
     * @sa process_adaptor
     *
     * @tparam Func Type of process to schedule.
     * @param func Either a lambda or a functor to use as a process.
     * @return An opaque object to use to concatenate processes.
     */
    template<typename Func>
    auto attach(Func &&func) {
        using Proc = process_adaptor<std::decay_t<Func>, Delta>;
        return attach<Proc>(std::forward<Func>(func));
    }

    /**
     * @brief Updates all scheduled processes.
     *
     * All scheduled processes are executed in no specific order.<br/>
     * If a process terminates with success, it's replaced with its child, if
     * any. Otherwise, if a process terminates with an error, it's removed along
     * with its child.
     *
     * @param delta Elapsed time.
     * @param data Optional data.
     */
    void update(const Delta delta, void *data = nullptr) {
        for(auto pos = handlers.size(); pos; --pos) {
            const auto curr = pos - 1u;

            if(const auto dead = handlers[curr].update(*this, curr, delta, data); dead) {
                std::swap(handlers[curr], handlers.back());
                handlers.pop_back();
            }
        }
    }

    /**
     * @brief Aborts all scheduled processes.
     *
     * Unless an immediate operation is requested, the abort is scheduled for
     * the next tick. Processes won't be executed anymore in any case.<br/>
     * Once a process is fully aborted and thus finished, it's discarded along
     * with its child, if any.
     *
     * @param immediately Requests an immediate operation.
     */
    void abort(const bool immediately = false) {
        for(auto pos = handlers.size(); pos; --pos) {
            const auto curr = pos - 1u;
            handlers[curr].abort(*this, curr, immediately);
        }
    }

private:
    std::vector<process_handler> handlers{};
};

} // namespace entt

#endif

// #include "resource/cache.hpp"
#ifndef ENTT_RESOURCE_RESOURCE_CACHE_HPP
#define ENTT_RESOURCE_RESOURCE_CACHE_HPP

#include <cstddef>
#include <functional>
#include <iterator>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../container/dense_map.hpp"
#ifndef ENTT_CONTAINER_DENSE_MAP_HPP
#define ENTT_CONTAINER_DENSE_MAP_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CONTAINER_FWD_HPP
#define ENTT_CONTAINER_FWD_HPP

#include <functional>
#include <memory>

namespace entt {

template<
    typename Key,
    typename Type,
    typename = std::hash<Key>,
    typename = std::equal_to<Key>,
    typename = std::allocator<std::pair<const Key, Type>>>
class dense_map;

template<
    typename Type,
    typename = std::hash<Type>,
    typename = std::equal_to<Type>,
    typename = std::allocator<Type>>
class dense_set;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Key, typename Type>
struct dense_map_node final {
    using value_type = std::pair<Key, Type>;

    template<typename... Args>
    dense_map_node(const std::size_t pos, Args &&...args)
        : next{pos},
          element{std::forward<Args>(args)...} {}

    template<typename Allocator, typename... Args>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const std::size_t pos, Args &&...args)
        : next{pos},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::forward<Args>(args)...)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const dense_map_node &other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, other.element)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, dense_map_node &&other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::move(other.element))} {}

    std::size_t next;
    value_type element;
};

template<typename It>
class dense_map_iterator final {
    template<typename>
    friend class dense_map_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_iterator() noexcept
        : it{} {}

    constexpr dense_map_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_iterator(const dense_map_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_map_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_map_iterator operator++(int) noexcept {
        dense_map_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_map_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_map_iterator operator--(int) noexcept {
        dense_map_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_map_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_map_iterator operator+(const difference_type value) const noexcept {
        dense_map_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_map_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_map_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].element.first, it[value].element.second};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->element.first, it->element.second};
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_map_local_iterator final {
    template<typename>
    friend class dense_map_local_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_map_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_local_iterator(const dense_map_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_map_local_iterator &operator++() noexcept {
        return offset = it[offset].next, *this;
    }

    constexpr dense_map_local_iterator operator++(int) noexcept {
        dense_map_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it[offset].element.first, it[offset].element.second};
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for key-value pairs with unique keys.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on the hash of its key. Keys with the same hash
 * code appear in the same bucket.
 *
 * @tparam Key Key type of the associative container.
 * @tparam Type Mapped type of the associative container.
 * @tparam Hash Type of function to use to hash the keys.
 * @tparam KeyEqual Type of function to use to compare the keys for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Key, typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_map {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = internal::dense_map_node<Key, Type>;
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::pair<const Key, Type>>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t key_to_bucket(const Other &key) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(key)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other, typename... Args>
    [[nodiscard]] auto insert_or_do_nothing(Other &&key, Args &&...args) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::piecewise_construct, std::forward_as_tuple(std::forward<Other>(key)), std::forward_as_tuple(std::forward<Args>(args)...));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    template<typename Other, typename Arg>
    [[nodiscard]] auto insert_or_overwrite(Other &&key, Arg &&value) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            it->second = std::forward<Arg>(value);
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(key), std::forward<Arg>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + key_to_bucket(packed.first().back().element.first);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].next) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Key;
    /*! @brief Mapped type of the container. */
    using mapped_type = Type;
    /*! @brief Key-value type of the container. */
    using value_type = std::pair<const Key, Type>;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the keys. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the keys for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Input iterator type. */
    using iterator = internal::dense_map_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_iterator = internal::dense_map_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Input iterator type. */
    using local_iterator = internal::dense_map_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_local_iterator = internal::dense_map_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_map()
        : dense_map{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const allocator_type &allocator)
        : dense_map{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const allocator_type &allocator)
        : dense_map{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_map{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_map(const dense_map &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_map(const dense_map &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_map(dense_map &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_map(dense_map &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_map &operator=(const dense_map &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_map &operator=(dense_map &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if the key does not exist.
     * @param value A key-value pair eventually convertible to the value type.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value.first, value.second);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value.first), std::move(value.second));
    }

    /**
     * @copydoc insert
     * @tparam Arg Type of the key-value pair to insert into the container.
     */
    template<typename Arg>
    std::enable_if_t<std::is_constructible_v<value_type, Arg &&>, std::pair<iterator, bool>>
    insert(Arg &&value) {
        return insert_or_do_nothing(std::forward<Arg>(value).first, std::forward<Arg>(value).second);
    }

    /**
     * @brief Inserts elements into the container, if their keys do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Inserts an element into the container or assigns to the current
     * element if the key already exists.
     * @tparam Arg Type of the value to insert or assign.
     * @param key A key used both to look up and to insert if not found.
     * @param value A value to insert or assign.
     * @return A pair consisting of an iterator to the element and a bool
     * denoting whether the insertion took place.
     */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(const key_type &key, Arg &&value) {
        return insert_or_overwrite(key, std::forward<Arg>(value));
    }

    /*! @copydoc insert_or_assign */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(key_type &&key, Arg &&value) {
        return insert_or_overwrite(std::move(key), std::forward<Arg>(value));
    }

    /**
     * @brief Constructs an element in-place, if the key does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace([[maybe_unused]] Args &&...args) {
        if constexpr(sizeof...(Args) == 0u) {
            return insert_or_do_nothing(key_type{});
        } else if constexpr(sizeof...(Args) == 1u) {
            return insert_or_do_nothing(std::forward<Args>(args).first..., std::forward<Args>(args).second...);
        } else if constexpr(sizeof...(Args) == 2u) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(packed.first().size(), std::forward<Args>(args)...);
            const auto index = key_to_bucket(node.element.first);

            if(auto it = constrained_find(node.element.first, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.next, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Inserts in-place if the key does not exist, does nothing if the
     * key exists.
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param key A key used both to look up and to insert if not found.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(const key_type &key, Args &&...args) {
        return insert_or_do_nothing(key, std::forward<Args>(args)...);
    }

    /*! @copydoc try_emplace */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(key_type &&key, Args &&...args) {
        return insert_or_do_nothing(std::move(key), std::forward<Args>(args)...);
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(pos->first);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].element.first);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given key.
     * @param key A key value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const key_type &key) {
        for(size_type *curr = sparse.first().data() + key_to_bucket(key); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].next) {
            if(packed.second()(packed.first()[*curr].element.first, key)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].next;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_map &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Accesses a given element with bounds checking.
     * @param key A key of an element to find.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &at(const key_type &key) {
        auto it = find(key);
        ENTT_ASSERT(it != end(), "Invalid key");
        return it->second;
    }

    /*! @copydoc at */
    [[nodiscard]] const mapped_type &at(const key_type &key) const {
        auto it = find(key);
        ENTT_ASSERT(it != cend(), "Invalid key");
        return it->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](const key_type &key) {
        return insert_or_do_nothing(key).first->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](key_type &&key) {
        return insert_or_do_nothing(std::move(key)).first->second;
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const key_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given key.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const key_type &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const key_type &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Finds an element with a key that compares _equivalent_ to a given
     * key.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Returns a range containing all elements with a given key.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const key_type &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const key_type &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given key.
     * @tparam Other Type of an element to search for.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given key.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const key_type &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Checks if the container contains an element with a key that
     * compares _equivalent_ to a given value.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given key.
     * @param key The value of the key to examine.
     * @return The bucket for the given key.
     */
    [[nodiscard]] size_type bucket(const key_type &key) const {
        return key_to_bucket(key);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = key_to_bucket(packed.first()[pos].element.first);
                packed.first()[pos].next = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the keys.
     * @return The function used to hash the keys.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare keys for equality.
     * @return The function used to compare keys for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace std {

template<typename Key, typename Value, typename Allocator>
struct uses_allocator<entt::internal::dense_map_node<Key, Value>, Allocator>
    : std::true_type {};

} // namespace std

/**
 * Internal details not to be documented.
 * @endcond
 */

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_RESOURCE_FWD_HPP
#define ENTT_RESOURCE_FWD_HPP

#include <memory>

namespace entt {

template<typename>
struct resource_loader;

template<typename Type, typename = resource_loader<Type>, typename = std::allocator<Type>>
class resource_cache;

template<typename>
class resource;

} // namespace entt

#endif

// #include "loader.hpp"
#ifndef ENTT_RESOURCE_LOADER_HPP
#define ENTT_RESOURCE_LOADER_HPP

#include <memory>
#include <utility>
// #include "fwd.hpp"


namespace entt {

/**
 * @brief Transparent loader for shared resources.
 * @tparam Type Type of resources created by the loader.
 */
template<typename Type>
struct resource_loader {
    /*! @brief Result type. */
    using result_type = std::shared_ptr<Type>;

    /**
     * @brief Constructs a shared pointer to a resource from its arguments.
     * @tparam Args Types of arguments to use to construct the resource.
     * @param args Parameters to use to construct the resource.
     * @return A shared pointer to a resource of the given type.
     */
    template<typename... Args>
    result_type operator()(Args &&...args) const {
        return std::make_shared<Type>(std::forward<Args>(args)...);
    }
};

} // namespace entt

#endif

// #include "resource.hpp"
#ifndef ENTT_RESOURCE_RESOURCE_HPP
#define ENTT_RESOURCE_RESOURCE_HPP

#include <memory>
#include <type_traits>
#include <utility>
// #include "fwd.hpp"


namespace entt {

/**
 * @brief Basic resource handle.
 *
 * A handle wraps a resource and extends its lifetime. It also shares the same
 * resource with all other handles constructed from the same element.<br/>
 * As a rule of thumb, resources should never be copied nor moved. Handles are
 * the way to go to push references around.
 *
 * @tparam Type Type of resource managed by a handle.
 */
template<typename Type>
class resource {
    /*! @brief Resource handles are friends with each other. */
    template<typename>
    friend class resource;

    template<typename Other>
    static constexpr bool is_acceptable_v = !std::is_same_v<Type, Other> && std::is_constructible_v<Type &, Other &>;

public:
    /*! @brief Resource type. */
    using element_type = Type;
    /*! @brief Handle type. */
    using handle_type = std::shared_ptr<element_type>;

    /*! @brief Default constructor. */
    resource() noexcept
        : value{} {}

    /**
     * @brief Creates a handle from a weak pointer, namely a resource.
     * @param res A weak pointer to a resource.
     */
    explicit resource(handle_type res) noexcept
        : value{std::move(res)} {}

    /*! @brief Default copy constructor. */
    resource(const resource &) noexcept = default;

    /*! @brief Default move constructor. */
    resource(resource &&) noexcept = default;

    /**
     * @brief Aliasing constructor.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle with which to share ownership information.
     * @param res Unrelated and unmanaged resources.
     */
    template<typename Other>
    resource(const resource<Other> &other, element_type &res) noexcept
        : value{other.value, std::addressof(res)} {}

    /**
     * @brief Copy constructs a handle which shares ownership of the resource.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle to copy from.
     */
    template<typename Other, typename = std::enable_if_t<is_acceptable_v<Other>>>
    resource(const resource<Other> &other) noexcept
        : value{other.value} {}

    /**
     * @brief Move constructs a handle which takes ownership of the resource.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle to move from.
     */
    template<typename Other, typename = std::enable_if_t<is_acceptable_v<Other>>>
    resource(resource<Other> &&other) noexcept
        : value{std::move(other.value)} {}

    /**
     * @brief Default copy assignment operator.
     * @return This resource handle.
     */
    resource &operator=(const resource &) noexcept = default;

    /**
     * @brief Default move assignment operator.
     * @return This resource handle.
     */
    resource &operator=(resource &&) noexcept = default;

    /**
     * @brief Copy assignment operator from foreign handle.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle to copy from.
     * @return This resource handle.
     */
    template<typename Other>
    std::enable_if_t<is_acceptable_v<Other>, resource &>
    operator=(const resource<Other> &other) noexcept {
        value = other.value;
        return *this;
    }

    /**
     * @brief Move assignment operator from foreign handle.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle to move from.
     * @return This resource handle.
     */
    template<typename Other>
    std::enable_if_t<is_acceptable_v<Other>, resource &>
    operator=(resource<Other> &&other) noexcept {
        value = std::move(other.value);
        return *this;
    }

    /**
     * @brief Returns a reference to the managed resource.
     *
     * @warning
     * The behavior is undefined if the handle doesn't contain a resource.
     *
     * @return A reference to the managed resource.
     */
    [[nodiscard]] element_type &operator*() const noexcept {
        return *value;
    }

    /*! @copydoc operator* */
    [[nodiscard]] operator element_type &() const noexcept {
        return *value;
    }

    /**
     * @brief Returns a pointer to the managed resource.
     * @return A pointer to the managed resource.
     */
    [[nodiscard]] element_type *operator->() const noexcept {
        return value.get();
    }

    /**
     * @brief Returns true if a handle contains a resource, false otherwise.
     * @return True if the handle contains a resource, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(value);
    }

    /**
     * @brief Returns the underlying resource handle.
     * @return The underlying resource handle.
     */
    [[nodiscard]] const handle_type &handle() const noexcept {
        return value;
    }

private:
    handle_type value;
};

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if both handles refer to the same resource, false otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator==(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return (std::addressof(*lhs) == std::addressof(*rhs));
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return False if both handles refer to the same registry, true otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator!=(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if the first handle is less than the second, false otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator<(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return (std::addressof(*lhs) < std::addressof(*rhs));
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if the first handle is greater than the second, false otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator>(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return (std::addressof(*lhs) > std::addressof(*rhs));
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if the first handle is less than or equal to the second, false
 * otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator<=(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return !(lhs > rhs);
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if the first handle is greater than or equal to the second,
 * false otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator>=(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return !(lhs < rhs);
}

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, typename It>
class resource_cache_iterator final {
    template<typename, typename>
    friend class resource_cache_iterator;

public:
    using value_type = std::pair<id_type, resource<Type>>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr resource_cache_iterator() noexcept = default;

    constexpr resource_cache_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr resource_cache_iterator(const resource_cache_iterator<std::remove_const_t<Type>, Other> &other) noexcept
        : it{other.it} {}

    constexpr resource_cache_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr resource_cache_iterator operator++(int) noexcept {
        resource_cache_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr resource_cache_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr resource_cache_iterator operator--(int) noexcept {
        resource_cache_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr resource_cache_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr resource_cache_iterator operator+(const difference_type value) const noexcept {
        resource_cache_iterator copy = *this;
        return (copy += value);
    }

    constexpr resource_cache_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr resource_cache_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].first, resource<Type>{it[value].second}};
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return (*this)[0];
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const resource_cache_iterator<TLhs, ILhs> &, const resource_cache_iterator<TRhs, IRhs> &) noexcept;

    template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
    friend constexpr bool operator==(const resource_cache_iterator<TLhs, ILhs> &, const resource_cache_iterator<TRhs, IRhs> &) noexcept;

    template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
    friend constexpr bool operator<(const resource_cache_iterator<TLhs, ILhs> &, const resource_cache_iterator<TRhs, IRhs> &) noexcept;

private:
    It it;
};

template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const resource_cache_iterator<TLhs, ILhs> &lhs, const resource_cache_iterator<TRhs, IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const resource_cache_iterator<TLhs, ILhs> &lhs, const resource_cache_iterator<TRhs, IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const resource_cache_iterator<TLhs, ILhs> &lhs, const resource_cache_iterator<TRhs, IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const resource_cache_iterator<TLhs, ILhs> &lhs, const resource_cache_iterator<TRhs, IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const resource_cache_iterator<TLhs, ILhs> &lhs, const resource_cache_iterator<TRhs, IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const resource_cache_iterator<TLhs, ILhs> &lhs, const resource_cache_iterator<TRhs, IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename TLhs, typename ILhs, typename TRhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const resource_cache_iterator<TLhs, ILhs> &lhs, const resource_cache_iterator<TRhs, IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic cache for resources of any type.
 * @tparam Type Type of resources managed by a cache.
 * @tparam Loader Type of loader used to create the resources.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Loader, typename Allocator>
class resource_cache {
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, Type>, "Invalid value type");
    using container_allocator = typename alloc_traits::template rebind_alloc<std::pair<const id_type, typename Loader::result_type>>;
    using container_type = dense_map<id_type, typename Loader::result_type, identity, std::equal_to<id_type>, container_allocator>;

public:
    /*! @brief Resource type. */
    using value_type = Type;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Loader type. */
    using loader_type = Loader;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Input iterator type. */
    using iterator = internal::resource_cache_iterator<Type, typename container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_iterator = internal::resource_cache_iterator<const Type, typename container_type::const_iterator>;

    /*! @brief Default constructor. */
    resource_cache()
        : resource_cache{loader_type{}} {}

    /**
     * @brief Constructs an empty cache with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit resource_cache(const allocator_type &allocator)
        : resource_cache{loader_type{}, allocator} {}

    /**
     * @brief Constructs an empty cache with a given allocator and loader.
     * @param callable The loader to use.
     * @param allocator The allocator to use.
     */
    explicit resource_cache(const loader_type &callable, const allocator_type &allocator = allocator_type{})
        : pool{container_type{allocator}, callable} {}

    /*! @brief Default copy constructor. */
    resource_cache(const resource_cache &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    resource_cache(const resource_cache &other, const allocator_type &allocator)
        : pool{std::piecewise_construct, std::forward_as_tuple(other.pool.first(), allocator), std::forward_as_tuple(other.pool.second())} {}

    /*! @brief Default move constructor. */
    resource_cache(resource_cache &&) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    resource_cache(resource_cache &&other, const allocator_type &allocator)
        : pool{std::piecewise_construct, std::forward_as_tuple(std::move(other.pool.first()), allocator), std::forward_as_tuple(std::move(other.pool.second()))} {}

    /**
     * @brief Default copy assignment operator.
     * @return This cache.
     */
    resource_cache &operator=(const resource_cache &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This cache.
     */
    resource_cache &operator=(resource_cache &&) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return pool.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the cache. If the
     * cache is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal cache.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return pool.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return pool.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the cache. Attempting to dereference the returned iterator results in
     * undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal cache.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return pool.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return pool.first().end();
    }

    /**
     * @brief Returns true if a cache contains no resources, false otherwise.
     * @return True if the cache contains no resources, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return pool.first().empty();
    }

    /**
     * @brief Number of resources managed by a cache.
     * @return Number of resources currently stored.
     */
    [[nodiscard]] size_type size() const noexcept {
        return pool.first().size();
    }

    /*! @brief Clears a cache. */
    void clear() noexcept {
        pool.first().clear();
    }

    /**
     * @brief Loads a resource, if its identifier does not exist.
     *
     * Arguments are forwarded directly to the loader and _consumed_ only if the
     * resource doesn't already exist.
     *
     * @warning
     * If the resource isn't loaded correctly, the returned handle could be
     * invalid and any use of it will result in undefined behavior.
     *
     * @tparam Args Types of arguments to use to load the resource if required.
     * @param id Unique resource identifier.
     * @param args Arguments to use to load the resource if required.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> load(const id_type id, Args &&...args) {
        if(auto it = pool.first().find(id); it != pool.first().end()) {
            return {it, false};
        }

        return pool.first().emplace(id, pool.second()(std::forward<Args>(args)...));
    }

    /**
     * @brief Force loads a resource, if its identifier does not exist.
     * @copydetails load
     */
    template<typename... Args>
    std::pair<iterator, bool> force_load(const id_type id, Args &&...args) {
        return {pool.first().insert_or_assign(id, pool.second()(std::forward<Args>(args)...)).first, true};
    }

    /**
     * @brief Returns a handle for a given resource identifier.
     *
     * @warning
     * There is no guarantee that the returned handle is valid.<br/>
     * If it is not, any use will result in indefinite behavior.
     *
     * @param id Unique resource identifier.
     * @return A handle for the given resource.
     */
    [[nodiscard]] resource<const value_type> operator[](const id_type id) const {
        if(auto it = pool.first().find(id); it != pool.first().cend()) {
            return resource<const value_type>{it->second};
        }

        return {};
    }

    /*! @copydoc operator[] */
    [[nodiscard]] resource<value_type> operator[](const id_type id) {
        if(auto it = pool.first().find(id); it != pool.first().end()) {
            return resource<value_type>{it->second};
        }

        return {};
    }

    /**
     * @brief Checks if a cache contains a given identifier.
     * @param id Unique resource identifier.
     * @return True if the cache contains the resource, false otherwise.
     */
    [[nodiscard]] bool contains(const id_type id) const {
        return pool.first().contains(id);
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto it = pool.first().begin();
        return pool.first().erase(it + (pos - const_iterator{it}));
    }

    /**
     * @brief Removes the given elements from a cache.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto it = pool.first().begin();
        return pool.first().erase(it + (first - const_iterator{it}), it + (last - const_iterator{it}));
    }

    /**
     * @brief Removes the given elements from a cache.
     * @param id Unique resource identifier.
     * @return Number of resources erased (either 0 or 1).
     */
    size_type erase(const id_type id) {
        return pool.first().erase(id);
    }

    /**
     * @brief Returns the loader used to create resources.
     * @return The loader used to create resources.
     */
    [[nodiscard]] loader_type loader() const {
        return pool.second();
    }

private:
    compressed_pair<container_type, loader_type> pool;
};

} // namespace entt

#endif

// #include "resource/loader.hpp"
#ifndef ENTT_RESOURCE_LOADER_HPP
#define ENTT_RESOURCE_LOADER_HPP

#include <memory>
#include <utility>
// #include "fwd.hpp"


namespace entt {

/**
 * @brief Transparent loader for shared resources.
 * @tparam Type Type of resources created by the loader.
 */
template<typename Type>
struct resource_loader {
    /*! @brief Result type. */
    using result_type = std::shared_ptr<Type>;

    /**
     * @brief Constructs a shared pointer to a resource from its arguments.
     * @tparam Args Types of arguments to use to construct the resource.
     * @param args Parameters to use to construct the resource.
     * @return A shared pointer to a resource of the given type.
     */
    template<typename... Args>
    result_type operator()(Args &&...args) const {
        return std::make_shared<Type>(std::forward<Args>(args)...);
    }
};

} // namespace entt

#endif

// #include "resource/resource.hpp"
#ifndef ENTT_RESOURCE_RESOURCE_HPP
#define ENTT_RESOURCE_RESOURCE_HPP

#include <memory>
#include <type_traits>
#include <utility>
// #include "fwd.hpp"


namespace entt {

/**
 * @brief Basic resource handle.
 *
 * A handle wraps a resource and extends its lifetime. It also shares the same
 * resource with all other handles constructed from the same element.<br/>
 * As a rule of thumb, resources should never be copied nor moved. Handles are
 * the way to go to push references around.
 *
 * @tparam Type Type of resource managed by a handle.
 */
template<typename Type>
class resource {
    /*! @brief Resource handles are friends with each other. */
    template<typename>
    friend class resource;

    template<typename Other>
    static constexpr bool is_acceptable_v = !std::is_same_v<Type, Other> && std::is_constructible_v<Type &, Other &>;

public:
    /*! @brief Resource type. */
    using element_type = Type;
    /*! @brief Handle type. */
    using handle_type = std::shared_ptr<element_type>;

    /*! @brief Default constructor. */
    resource() noexcept
        : value{} {}

    /**
     * @brief Creates a handle from a weak pointer, namely a resource.
     * @param res A weak pointer to a resource.
     */
    explicit resource(handle_type res) noexcept
        : value{std::move(res)} {}

    /*! @brief Default copy constructor. */
    resource(const resource &) noexcept = default;

    /*! @brief Default move constructor. */
    resource(resource &&) noexcept = default;

    /**
     * @brief Aliasing constructor.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle with which to share ownership information.
     * @param res Unrelated and unmanaged resources.
     */
    template<typename Other>
    resource(const resource<Other> &other, element_type &res) noexcept
        : value{other.value, std::addressof(res)} {}

    /**
     * @brief Copy constructs a handle which shares ownership of the resource.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle to copy from.
     */
    template<typename Other, typename = std::enable_if_t<is_acceptable_v<Other>>>
    resource(const resource<Other> &other) noexcept
        : value{other.value} {}

    /**
     * @brief Move constructs a handle which takes ownership of the resource.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle to move from.
     */
    template<typename Other, typename = std::enable_if_t<is_acceptable_v<Other>>>
    resource(resource<Other> &&other) noexcept
        : value{std::move(other.value)} {}

    /**
     * @brief Default copy assignment operator.
     * @return This resource handle.
     */
    resource &operator=(const resource &) noexcept = default;

    /**
     * @brief Default move assignment operator.
     * @return This resource handle.
     */
    resource &operator=(resource &&) noexcept = default;

    /**
     * @brief Copy assignment operator from foreign handle.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle to copy from.
     * @return This resource handle.
     */
    template<typename Other>
    std::enable_if_t<is_acceptable_v<Other>, resource &>
    operator=(const resource<Other> &other) noexcept {
        value = other.value;
        return *this;
    }

    /**
     * @brief Move assignment operator from foreign handle.
     * @tparam Other Type of resource managed by the received handle.
     * @param other The handle to move from.
     * @return This resource handle.
     */
    template<typename Other>
    std::enable_if_t<is_acceptable_v<Other>, resource &>
    operator=(resource<Other> &&other) noexcept {
        value = std::move(other.value);
        return *this;
    }

    /**
     * @brief Returns a reference to the managed resource.
     *
     * @warning
     * The behavior is undefined if the handle doesn't contain a resource.
     *
     * @return A reference to the managed resource.
     */
    [[nodiscard]] element_type &operator*() const noexcept {
        return *value;
    }

    /*! @copydoc operator* */
    [[nodiscard]] operator element_type &() const noexcept {
        return *value;
    }

    /**
     * @brief Returns a pointer to the managed resource.
     * @return A pointer to the managed resource.
     */
    [[nodiscard]] element_type *operator->() const noexcept {
        return value.get();
    }

    /**
     * @brief Returns true if a handle contains a resource, false otherwise.
     * @return True if the handle contains a resource, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(value);
    }

    /**
     * @brief Returns the underlying resource handle.
     * @return The underlying resource handle.
     */
    [[nodiscard]] const handle_type &handle() const noexcept {
        return value;
    }

private:
    handle_type value;
};

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if both handles refer to the same resource, false otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator==(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return (std::addressof(*lhs) == std::addressof(*rhs));
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return False if both handles refer to the same registry, true otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator!=(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if the first handle is less than the second, false otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator<(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return (std::addressof(*lhs) < std::addressof(*rhs));
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if the first handle is greater than the second, false otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator>(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return (std::addressof(*lhs) > std::addressof(*rhs));
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if the first handle is less than or equal to the second, false
 * otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator<=(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return !(lhs > rhs);
}

/**
 * @brief Compares two handles.
 * @tparam Res Type of resource managed by the first handle.
 * @tparam Other Type of resource managed by the second handle.
 * @param lhs A valid handle.
 * @param rhs A valid handle.
 * @return True if the first handle is greater than or equal to the second,
 * false otherwise.
 */
template<typename Res, typename Other>
[[nodiscard]] bool operator>=(const resource<Res> &lhs, const resource<Other> &rhs) noexcept {
    return !(lhs < rhs);
}

} // namespace entt

#endif

// #include "signal/delegate.hpp"
#ifndef ENTT_SIGNAL_DELEGATE_HPP
#define ENTT_SIGNAL_DELEGATE_HPP

#include <cstddef>
#include <functional>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_SIGNAL_FWD_HPP
#define ENTT_SIGNAL_FWD_HPP

#include <memory>

namespace entt {

template<typename>
class delegate;

template<typename = std::allocator<void>>
class basic_dispatcher;

template<typename, typename = std::allocator<void>>
class emitter;

class connection;

struct scoped_connection;

template<typename>
class sink;

template<typename Type, typename = std::allocator<void>>
class sigh;

/*! @brief Alias declaration for the most common use case. */
using dispatcher = basic_dispatcher<>;

/*! @brief Disambiguation tag for constructors and the like. */
template<auto>
struct connect_arg_t {
    /*! @brief Default constructor. */
    explicit connect_arg_t() = default;
};

/**
 * @brief Constant of type connect_arg_t used to disambiguate calls.
 * @tparam Candidate Element to connect (likely a free or member function).
 */
template<auto Candidate>
inline constexpr connect_arg_t<Candidate> connect_arg{};

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Ret, typename... Args>
constexpr auto function_pointer(Ret (*)(Args...)) -> Ret (*)(Args...);

template<typename Ret, typename Type, typename... Args, typename Other>
constexpr auto function_pointer(Ret (*)(Type, Args...), Other &&) -> Ret (*)(Args...);

template<typename Class, typename Ret, typename... Args, typename... Other>
constexpr auto function_pointer(Ret (Class::*)(Args...), Other &&...) -> Ret (*)(Args...);

template<typename Class, typename Ret, typename... Args, typename... Other>
constexpr auto function_pointer(Ret (Class::*)(Args...) const, Other &&...) -> Ret (*)(Args...);

template<typename Class, typename Type, typename... Other>
constexpr auto function_pointer(Type Class::*, Other &&...) -> Type (*)();

template<typename... Type>
using function_pointer_t = decltype(function_pointer(std::declval<Type>()...));

template<typename... Class, typename Ret, typename... Args>
[[nodiscard]] constexpr auto index_sequence_for(Ret (*)(Args...)) {
    return std::index_sequence_for<Class..., Args...>{};
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic delegate implementation.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 */
template<typename>
class delegate;

/**
 * @brief Utility class to use to send around functions and members.
 *
 * Unmanaged delegate for function pointers and members. Users of this class are
 * in charge of disconnecting instances before deleting them.
 *
 * A delegate can be used as a general purpose invoker without memory overhead
 * for free functions possibly with payloads and bound or unbound members.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 */
template<typename Ret, typename... Args>
class delegate<Ret(Args...)> {
    template<auto Candidate, std::size_t... Index>
    [[nodiscard]] auto wrap(std::index_sequence<Index...>) noexcept {
        return [](const void *, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            return static_cast<Ret>(std::invoke(Candidate, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

    template<auto Candidate, typename Type, std::size_t... Index>
    [[nodiscard]] auto wrap(Type &, std::index_sequence<Index...>) noexcept {
        return [](const void *payload, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            return static_cast<Ret>(std::invoke(Candidate, *curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

    template<auto Candidate, typename Type, std::size_t... Index>
    [[nodiscard]] auto wrap(Type *, std::index_sequence<Index...>) noexcept {
        return [](const void *payload, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            return static_cast<Ret>(std::invoke(Candidate, curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

public:
    /*! @brief Function type of the contained target. */
    using function_type = Ret(const void *, Args...);
    /*! @brief Function type of the delegate. */
    using type = Ret(Args...);
    /*! @brief Return type of the delegate. */
    using result_type = Ret;

    /*! @brief Default constructor. */
    delegate() noexcept
        : instance{nullptr},
          fn{nullptr} {}

    /**
     * @brief Constructs a delegate with a given object or payload, if any.
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance Optional valid object that fits the purpose.
     */
    template<auto Candidate, typename... Type>
    delegate(connect_arg_t<Candidate>, Type &&...value_or_instance) noexcept {
        connect<Candidate>(std::forward<Type>(value_or_instance)...);
    }

    /**
     * @brief Constructs a delegate and connects an user defined function with
     * optional payload.
     * @param function Function to connect to the delegate.
     * @param payload User defined arbitrary data.
     */
    delegate(function_type *function, const void *payload = nullptr) noexcept {
        connect(function, payload);
    }

    /**
     * @brief Connects a free function or an unbound member to a delegate.
     * @tparam Candidate Function or member to connect to the delegate.
     */
    template<auto Candidate>
    void connect() noexcept {
        instance = nullptr;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
            fn = [](const void *, Args... args) -> Ret {
                return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
            };
        } else if constexpr(std::is_member_pointer_v<decltype(Candidate)>) {
            fn = wrap<Candidate>(internal::index_sequence_for<type_list_element_t<0, type_list<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
        } else {
            fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
        }
    }

    /**
     * @brief Connects a free function with payload or a bound member to a
     * delegate.
     *
     * The delegate isn't responsible for the connected object or the payload.
     * Users must always guarantee that the lifetime of the instance overcomes
     * the one of the delegate.<br/>
     * When used to connect a free function with payload, its signature must be
     * such that the instance is the first argument before the ones used to
     * define the delegate itself.
     *
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid reference that fits the purpose.
     */
    template<auto Candidate, typename Type>
    void connect(Type &value_or_instance) noexcept {
        instance = &value_or_instance;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type &, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
                return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }

    /**
     * @brief Connects a free function with payload or a bound member to a
     * delegate.
     *
     * @sa connect(Type &)
     *
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid pointer that fits the purpose.
     */
    template<auto Candidate, typename Type>
    void connect(Type *value_or_instance) noexcept {
        instance = value_or_instance;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type *, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
                return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }

    /**
     * @brief Connects an user defined function with optional payload to a
     * delegate.
     *
     * The delegate isn't responsible for the connected object or the payload.
     * Users must always guarantee that the lifetime of an instance overcomes
     * the one of the delegate.<br/>
     * The payload is returned as the first argument to the target function in
     * all cases.
     *
     * @param function Function to connect to the delegate.
     * @param payload User defined arbitrary data.
     */
    void connect(function_type *function, const void *payload = nullptr) noexcept {
        ENTT_ASSERT(function != nullptr, "Uninitialized function pointer");
        instance = payload;
        fn = function;
    }

    /**
     * @brief Resets a delegate.
     *
     * After a reset, a delegate cannot be invoked anymore.
     */
    void reset() noexcept {
        instance = nullptr;
        fn = nullptr;
    }

    /**
     * @brief Returns the instance or the payload linked to a delegate, if any.
     * @return An opaque pointer to the underlying data.
     */
    [[nodiscard]] const void *data() const noexcept {
        return instance;
    }

    /**
     * @brief Triggers a delegate.
     *
     * The delegate invokes the underlying function and returns the result.
     *
     * @warning
     * Attempting to trigger an invalid delegate results in undefined
     * behavior.
     *
     * @param args Arguments to use to invoke the underlying function.
     * @return The value returned by the underlying function.
     */
    Ret operator()(Args... args) const {
        ENTT_ASSERT(static_cast<bool>(*this), "Uninitialized delegate");
        return fn(instance, std::forward<Args>(args)...);
    }

    /**
     * @brief Checks whether a delegate actually stores a listener.
     * @return False if the delegate is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        // no need to also test instance
        return !(fn == nullptr);
    }

    /**
     * @brief Compares the contents of two delegates.
     * @param other Delegate with which to compare.
     * @return False if the two contents differ, true otherwise.
     */
    [[nodiscard]] bool operator==(const delegate<Ret(Args...)> &other) const noexcept {
        return fn == other.fn && instance == other.instance;
    }

private:
    const void *instance;
    function_type *fn;
};

/**
 * @brief Compares the contents of two delegates.
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @param lhs A valid delegate object.
 * @param rhs A valid delegate object.
 * @return True if the two contents differ, false otherwise.
 */
template<typename Ret, typename... Args>
[[nodiscard]] bool operator!=(const delegate<Ret(Args...)> &lhs, const delegate<Ret(Args...)> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Deduction guide.
 * @tparam Candidate Function or member to connect to the delegate.
 */
template<auto Candidate>
delegate(connect_arg_t<Candidate>) -> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;

/**
 * @brief Deduction guide.
 * @tparam Candidate Function or member to connect to the delegate.
 * @tparam Type Type of class or type of payload.
 */
template<auto Candidate, typename Type>
delegate(connect_arg_t<Candidate>, Type &&) -> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;

/**
 * @brief Deduction guide.
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 */
template<typename Ret, typename... Args>
delegate(Ret (*)(const void *, Args...), const void * = nullptr) -> delegate<Ret(Args...)>;

} // namespace entt

#endif

// #include "signal/dispatcher.hpp"
#ifndef ENTT_SIGNAL_DISPATCHER_HPP
#define ENTT_SIGNAL_DISPATCHER_HPP

#include <cstddef>
#include <functional>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../container/dense_map.hpp"
#ifndef ENTT_CONTAINER_DENSE_MAP_HPP
#define ENTT_CONTAINER_DENSE_MAP_HPP

#include <cmath>
#include <cstddef>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"
#ifndef ENTT_CONFIG_CONFIG_H
#define ENTT_CONFIG_CONFIG_H

// #include "version.h"
#ifndef ENTT_CONFIG_VERSION_H
#define ENTT_CONFIG_VERSION_H

// #include "macro.h"
#ifndef ENTT_CONFIG_MACRO_H
#define ENTT_CONFIG_MACRO_H

#define ENTT_STR(arg) #arg
#define ENTT_XSTR(arg) ENTT_STR(arg)

#endif


#define ENTT_VERSION_MAJOR 3
#define ENTT_VERSION_MINOR 11
#define ENTT_VERSION_PATCH 1

#define ENTT_VERSION \
    ENTT_XSTR(ENTT_VERSION_MAJOR) \
    "." ENTT_XSTR(ENTT_VERSION_MINOR) "." ENTT_XSTR(ENTT_VERSION_PATCH)

#endif


#if defined(__cpp_exceptions) && !defined(ENTT_NOEXCEPTION)
#    define ENTT_CONSTEXPR
#    define ENTT_THROW throw
#    define ENTT_TRY try
#    define ENTT_CATCH catch(...)
#else
#    define ENTT_CONSTEXPR constexpr // use only with throwing functions (waiting for C++20)
#    define ENTT_THROW
#    define ENTT_TRY if(true)
#    define ENTT_CATCH if(false)
#endif

#ifdef ENTT_USE_ATOMIC
#    include <atomic>
#    define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
#else
#    define ENTT_MAYBE_ATOMIC(Type) Type
#endif

#ifndef ENTT_ID_TYPE
#    include <cstdint>
#    define ENTT_ID_TYPE std::uint32_t
#endif

#ifndef ENTT_SPARSE_PAGE
#    define ENTT_SPARSE_PAGE 4096
#endif

#ifndef ENTT_PACKED_PAGE
#    define ENTT_PACKED_PAGE 1024
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT
#    define ENTT_ASSERT(condition, msg) (void(0))
#elif !defined ENTT_ASSERT
#    include <cassert>
#    define ENTT_ASSERT(condition, msg) assert(condition)
#endif

#ifdef ENTT_DISABLE_ASSERT
#    undef ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) (void(0))
#elif !defined ENTT_ASSERT_CONSTEXPR
#    define ENTT_ASSERT_CONSTEXPR(condition, msg) ENTT_ASSERT(condition, msg)
#endif

#ifdef ENTT_NO_ETO
#    define ENTT_ETO_TYPE(Type) void
#else
#    define ENTT_ETO_TYPE(Type) Type
#endif

#ifdef ENTT_STANDARD_CPP
#    define ENTT_NONSTD false
#else
#    define ENTT_NONSTD true
#    if defined __clang__ || defined __GNUC__
#        define ENTT_PRETTY_FUNCTION __PRETTY_FUNCTION__
#        define ENTT_PRETTY_FUNCTION_PREFIX '='
#        define ENTT_PRETTY_FUNCTION_SUFFIX ']'
#    elif defined _MSC_VER
#        define ENTT_PRETTY_FUNCTION __FUNCSIG__
#        define ENTT_PRETTY_FUNCTION_PREFIX '<'
#        define ENTT_PRETTY_FUNCTION_SUFFIX '>'
#    endif
#endif

#if defined _MSC_VER
#    pragma detect_mismatch("entt.version", ENTT_VERSION)
#    pragma detect_mismatch("entt.noexcept", ENTT_XSTR(ENTT_TRY))
#    pragma detect_mismatch("entt.id", ENTT_XSTR(ENTT_ID_TYPE))
#    pragma detect_mismatch("entt.nonstd", ENTT_XSTR(ENTT_NONSTD))
#endif

#endif

// #include "fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/iterator.hpp"
#ifndef ENTT_CORE_ITERATOR_HPP
#define ENTT_CORE_ITERATOR_HPP

#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>

namespace entt {

/**
 * @brief Helper type to use as pointer with input iterators.
 * @tparam Type of wrapped value.
 */
template<typename Type>
struct input_iterator_pointer final {
    /*! @brief Value type. */
    using value_type = Type;
    /*! @brief Pointer type. */
    using pointer = Type *;
    /*! @brief Reference type. */
    using reference = Type &;

    /**
     * @brief Constructs a proxy object by move.
     * @param val Value to use to initialize the proxy object.
     */
    constexpr input_iterator_pointer(value_type &&val) noexcept(std::is_nothrow_move_constructible_v<value_type>)
        : value{std::move(val)} {}

    /**
     * @brief Access operator for accessing wrapped values.
     * @return A pointer to the wrapped value.
     */
    [[nodiscard]] constexpr pointer operator->() noexcept {
        return std::addressof(value);
    }

    /**
     * @brief Dereference operator for accessing wrapped values.
     * @return A reference to the wrapped value.
     */
    [[nodiscard]] constexpr reference operator*() noexcept {
        return value;
    }

private:
    Type value;
};

/**
 * @brief Plain iota iterator (waiting for C++20).
 * @tparam Type Value type.
 */
template<typename Type>
class iota_iterator final {
    static_assert(std::is_integral_v<Type>, "Not an integral type");

public:
    /*! @brief Value type, likely an integral one. */
    using value_type = Type;
    /*! @brief Invalid pointer type. */
    using pointer = void;
    /*! @brief Non-reference type, same as value type. */
    using reference = value_type;
    /*! @brief Difference type. */
    using difference_type = std::ptrdiff_t;
    /*! @brief Iterator category. */
    using iterator_category = std::input_iterator_tag;

    /*! @brief Default constructor. */
    constexpr iota_iterator() noexcept
        : current{} {}

    /**
     * @brief Constructs an iota iterator from a given value.
     * @param init The initial value assigned to the iota iterator.
     */
    constexpr iota_iterator(const value_type init) noexcept
        : current{init} {}

    /**
     * @brief Pre-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator &operator++() noexcept {
        return ++current, *this;
    }

    /**
     * @brief Post-increment operator.
     * @return This iota iterator.
     */
    constexpr iota_iterator operator++(int) noexcept {
        iota_iterator orig = *this;
        return ++(*this), orig;
    }

    /**
     * @brief Dereference operator.
     * @return The underlying value.
     */
    [[nodiscard]] constexpr reference operator*() const noexcept {
        return current;
    }

private:
    value_type current;
};

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators are identical, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator==(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return *lhs == *rhs;
}

/**
 * @brief Comparison operator.
 * @tparam Type Value type of the iota iterator.
 * @param lhs A properly initialized iota iterator.
 * @param rhs A properly initialized iota iterator.
 * @return True if the two iterators differ, false otherwise.
 */
template<typename Type>
[[nodiscard]] constexpr bool operator!=(const iota_iterator<Type> &lhs, const iota_iterator<Type> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Utility class to create an iterable object from a pair of iterators.
 * @tparam It Type of iterator.
 * @tparam Sentinel Type of sentinel.
 */
template<typename It, typename Sentinel = It>
struct iterable_adaptor final {
    /*! @brief Value type. */
    using value_type = typename std::iterator_traits<It>::value_type;
    /*! @brief Iterator type. */
    using iterator = It;
    /*! @brief Sentinel type. */
    using sentinel = Sentinel;

    /*! @brief Default constructor. */
    constexpr iterable_adaptor() noexcept(std::is_nothrow_default_constructible_v<iterator> &&std::is_nothrow_default_constructible_v<sentinel>)
        : first{},
          last{} {}

    /**
     * @brief Creates an iterable object from a pair of iterators.
     * @param from Begin iterator.
     * @param to End iterator.
     */
    constexpr iterable_adaptor(iterator from, sentinel to) noexcept(std::is_nothrow_move_constructible_v<iterator> &&std::is_nothrow_move_constructible_v<sentinel>)
        : first{std::move(from)},
          last{std::move(to)} {}

    /**
     * @brief Returns an iterator to the beginning.
     * @return An iterator to the first element of the range.
     */
    [[nodiscard]] constexpr iterator begin() const noexcept {
        return first;
    }

    /**
     * @brief Returns an iterator to the end.
     * @return An iterator to the element following the last element of the
     * range.
     */
    [[nodiscard]] constexpr sentinel end() const noexcept {
        return last;
    }

    /*! @copydoc begin */
    [[nodiscard]] constexpr iterator cbegin() const noexcept {
        return begin();
    }

    /*! @copydoc end */
    [[nodiscard]] constexpr sentinel cend() const noexcept {
        return end();
    }

private:
    It first;
    Sentinel last;
};

} // namespace entt

#endif

// #include "../core/memory.hpp"
#ifndef ENTT_CORE_MEMORY_HPP
#define ENTT_CORE_MEMORY_HPP

#include <cstddef>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"


namespace entt {

/**
 * @brief Checks whether a value is a power of two or not.
 * @param value A value that may or may not be a power of two.
 * @return True if the value is a power of two, false otherwise.
 */
[[nodiscard]] inline constexpr bool is_power_of_two(const std::size_t value) noexcept {
    return value && ((value & (value - 1)) == 0);
}

/**
 * @brief Computes the smallest power of two greater than or equal to a value.
 * @param value The value to use.
 * @return The smallest power of two greater than or equal to the given value.
 */
[[nodiscard]] inline constexpr std::size_t next_power_of_two(const std::size_t value) noexcept {
    ENTT_ASSERT_CONSTEXPR(value < (std::size_t{1u} << (std::numeric_limits<std::size_t>::digits - 1)), "Numeric limits exceeded");
    std::size_t curr = value - (value != 0u);

    for(int next = 1; next < std::numeric_limits<std::size_t>::digits; next = next * 2) {
        curr |= curr >> next;
    }

    return ++curr;
}

/**
 * @brief Fast module utility function (powers of two only).
 * @param value A value for which to calculate the modulus.
 * @param mod _Modulus_, it must be a power of two.
 * @return The common remainder.
 */
[[nodiscard]] inline constexpr std::size_t fast_mod(const std::size_t value, const std::size_t mod) noexcept {
    ENTT_ASSERT_CONSTEXPR(is_power_of_two(mod), "Value must be a power of two");
    return value & (mod - 1u);
}

/**
 * @brief Unwraps fancy pointers, does nothing otherwise (waiting for C++20).
 * @tparam Type Pointer type.
 * @param ptr Fancy or raw pointer.
 * @return A raw pointer that represents the address of the original pointer.
 */
template<typename Type>
[[nodiscard]] constexpr auto to_address(Type &&ptr) noexcept {
    if constexpr(std::is_pointer_v<std::decay_t<Type>>) {
        return ptr;
    } else {
        return to_address(std::forward<Type>(ptr).operator->());
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_copy_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_copy_assignment::value) {
        lhs = rhs;
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_move_assignment([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) {
        lhs = std::move(rhs);
    }
}

/**
 * @brief Utility function to design allocation-aware containers.
 * @tparam Allocator Type of allocator.
 * @param lhs A valid allocator.
 * @param rhs Another valid allocator.
 */
template<typename Allocator>
constexpr void propagate_on_container_swap([[maybe_unused]] Allocator &lhs, [[maybe_unused]] Allocator &rhs) noexcept {
    if constexpr(std::allocator_traits<Allocator>::propagate_on_container_swap::value) {
        using std::swap;
        swap(lhs, rhs);
    } else {
        ENTT_ASSERT_CONSTEXPR(lhs == rhs, "Cannot swap the containers");
    }
}

/**
 * @brief Deleter for allocator-aware unique pointers (waiting for C++20).
 * @tparam Args Types of arguments to use to construct the object.
 */
template<typename Allocator>
struct allocation_deleter: private Allocator {
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Pointer type. */
    using pointer = typename std::allocator_traits<Allocator>::pointer;

    /**
     * @brief Inherited constructors.
     * @param alloc The allocator to use.
     */
    constexpr allocation_deleter(const allocator_type &alloc) noexcept(std::is_nothrow_copy_constructible_v<allocator_type>)
        : Allocator{alloc} {}

    /**
     * @brief Destroys the pointed object and deallocates its memory.
     * @param ptr A valid pointer to an object of the given type.
     */
    constexpr void operator()(pointer ptr) noexcept(std::is_nothrow_destructible_v<typename allocator_type::value_type>) {
        using alloc_traits = typename std::allocator_traits<Allocator>;
        alloc_traits::destroy(*this, to_address(ptr));
        alloc_traits::deallocate(*this, ptr, 1u);
    }
};

/**
 * @brief Allows `std::unique_ptr` to use allocators (waiting for C++20).
 * @tparam Type Type of object to allocate for and to construct.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A properly initialized unique pointer with a custom deleter.
 */
template<typename Type, typename Allocator, typename... Args>
ENTT_CONSTEXPR auto allocate_unique(Allocator &allocator, Args &&...args) {
    static_assert(!std::is_array_v<Type>, "Array types are not supported");

    using alloc_traits = typename std::allocator_traits<Allocator>::template rebind_traits<Type>;
    using allocator_type = typename alloc_traits::allocator_type;

    allocator_type alloc{allocator};
    auto ptr = alloc_traits::allocate(alloc, 1u);

    ENTT_TRY {
        alloc_traits::construct(alloc, to_address(ptr), std::forward<Args>(args)...);
    }
    ENTT_CATCH {
        alloc_traits::deallocate(alloc, ptr, 1u);
        ENTT_THROW;
    }

    return std::unique_ptr<Type, allocation_deleter<allocator_type>>{ptr, alloc};
}

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type>
struct uses_allocator_construction {
    template<typename Allocator, typename... Params>
    static constexpr auto args([[maybe_unused]] const Allocator &allocator, Params &&...params) noexcept {
        if constexpr(!std::uses_allocator_v<Type, Allocator> && std::is_constructible_v<Type, Params...>) {
            return std::forward_as_tuple(std::forward<Params>(params)...);
        } else {
            static_assert(std::uses_allocator_v<Type, Allocator>, "Ill-formed request");

            if constexpr(std::is_constructible_v<Type, std::allocator_arg_t, const Allocator &, Params...>) {
                return std::tuple<std::allocator_arg_t, const Allocator &, Params &&...>{std::allocator_arg, allocator, std::forward<Params>(params)...};
            } else {
                static_assert(std::is_constructible_v<Type, Params..., const Allocator &>, "Ill-formed request");
                return std::forward_as_tuple(std::forward<Params>(params)..., allocator);
            }
        }
    }
};

template<typename Type, typename Other>
struct uses_allocator_construction<std::pair<Type, Other>> {
    using type = std::pair<Type, Other>;

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::piecewise_construct_t, First &&first, Second &&second) noexcept {
        return std::make_tuple(
            std::piecewise_construct,
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Type>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<First>(first)),
            std::apply([&allocator](auto &&...curr) { return uses_allocator_construction<Other>::args(allocator, std::forward<decltype(curr)>(curr)...); }, std::forward<Second>(second)));
    }

    template<typename Allocator>
    static constexpr auto args(const Allocator &allocator) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::tuple<>{}, std::tuple<>{});
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, First &&first, Second &&second) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::forward<First>(first)), std::forward_as_tuple(std::forward<Second>(second)));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, const std::pair<First, Second> &value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(value.first), std::forward_as_tuple(value.second));
    }

    template<typename Allocator, typename First, typename Second>
    static constexpr auto args(const Allocator &allocator, std::pair<First, Second> &&value) noexcept {
        return uses_allocator_construction<type>::args(allocator, std::piecewise_construct, std::forward_as_tuple(std::move(value.first)), std::forward_as_tuple(std::move(value.second)));
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Prepares the argument list needed to
 * create an object of a given type by means of uses-allocator construction.
 *
 * @tparam Type Type to return arguments for.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return The arguments needed to create an object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr auto uses_allocator_construction_args(const Allocator &allocator, Args &&...args) noexcept {
    return internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...);
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type make_obj_using_allocator(const Allocator &allocator, Args &&...args) {
    return std::make_from_tuple<Type>(internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

/**
 * @brief Uses-allocator construction utility (waiting for C++20).
 *
 * Primarily intended for internal use. Creates an object of a given type by
 * means of uses-allocator construction at an uninitialized memory location.
 *
 * @tparam Type Type of object to create.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 * @tparam Args Types of arguments to use to construct the object.
 * @param value Memory location in which to place the object.
 * @param allocator The allocator to use.
 * @param args Parameters to use to construct the object.
 * @return A pointer to the newly created object of the given type.
 */
template<typename Type, typename Allocator, typename... Args>
constexpr Type *uninitialized_construct_using_allocator(Type *value, const Allocator &allocator, Args &&...args) {
    return std::apply([value](auto &&...curr) { return new(value) Type(std::forward<decltype(curr)>(curr)...); }, internal::uses_allocator_construction<Type>::args(allocator, std::forward<Args>(args)...));
}

} // namespace entt

#endif

// #include "../core/type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif

// #include "fwd.hpp"
#ifndef ENTT_CONTAINER_FWD_HPP
#define ENTT_CONTAINER_FWD_HPP

#include <functional>
#include <memory>

namespace entt {

template<
    typename Key,
    typename Type,
    typename = std::hash<Key>,
    typename = std::equal_to<Key>,
    typename = std::allocator<std::pair<const Key, Type>>>
class dense_map;

template<
    typename Type,
    typename = std::hash<Type>,
    typename = std::equal_to<Type>,
    typename = std::allocator<Type>>
class dense_set;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Key, typename Type>
struct dense_map_node final {
    using value_type = std::pair<Key, Type>;

    template<typename... Args>
    dense_map_node(const std::size_t pos, Args &&...args)
        : next{pos},
          element{std::forward<Args>(args)...} {}

    template<typename Allocator, typename... Args>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const std::size_t pos, Args &&...args)
        : next{pos},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::forward<Args>(args)...)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, const dense_map_node &other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, other.element)} {}

    template<typename Allocator>
    dense_map_node(std::allocator_arg_t, const Allocator &allocator, dense_map_node &&other)
        : next{other.next},
          element{entt::make_obj_using_allocator<value_type>(allocator, std::move(other.element))} {}

    std::size_t next;
    value_type element;
};

template<typename It>
class dense_map_iterator final {
    template<typename>
    friend class dense_map_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_iterator() noexcept
        : it{} {}

    constexpr dense_map_iterator(const It iter) noexcept
        : it{iter} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_iterator(const dense_map_iterator<Other> &other) noexcept
        : it{other.it} {}

    constexpr dense_map_iterator &operator++() noexcept {
        return ++it, *this;
    }

    constexpr dense_map_iterator operator++(int) noexcept {
        dense_map_iterator orig = *this;
        return ++(*this), orig;
    }

    constexpr dense_map_iterator &operator--() noexcept {
        return --it, *this;
    }

    constexpr dense_map_iterator operator--(int) noexcept {
        dense_map_iterator orig = *this;
        return operator--(), orig;
    }

    constexpr dense_map_iterator &operator+=(const difference_type value) noexcept {
        it += value;
        return *this;
    }

    constexpr dense_map_iterator operator+(const difference_type value) const noexcept {
        dense_map_iterator copy = *this;
        return (copy += value);
    }

    constexpr dense_map_iterator &operator-=(const difference_type value) noexcept {
        return (*this += -value);
    }

    constexpr dense_map_iterator operator-(const difference_type value) const noexcept {
        return (*this + -value);
    }

    [[nodiscard]] constexpr reference operator[](const difference_type value) const noexcept {
        return {it[value].element.first, it[value].element.second};
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it->element.first, it->element.second};
    }

    template<typename ILhs, typename IRhs>
    friend constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator==(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

    template<typename ILhs, typename IRhs>
    friend constexpr bool operator<(const dense_map_iterator<ILhs> &, const dense_map_iterator<IRhs> &) noexcept;

private:
    It it;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr std::ptrdiff_t operator-(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it - rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it == rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return lhs.it < rhs.it;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return rhs < lhs;
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator<=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs > rhs);
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator>=(const dense_map_iterator<ILhs> &lhs, const dense_map_iterator<IRhs> &rhs) noexcept {
    return !(lhs < rhs);
}

template<typename It>
class dense_map_local_iterator final {
    template<typename>
    friend class dense_map_local_iterator;

    using first_type = decltype(std::as_const(std::declval<It>()->element.first));
    using second_type = decltype((std::declval<It>()->element.second));

public:
    using value_type = std::pair<first_type, second_type>;
    using pointer = input_iterator_pointer<value_type>;
    using reference = value_type;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::input_iterator_tag;

    constexpr dense_map_local_iterator() noexcept
        : it{},
          offset{} {}

    constexpr dense_map_local_iterator(It iter, const std::size_t pos) noexcept
        : it{iter},
          offset{pos} {}

    template<typename Other, typename = std::enable_if_t<!std::is_same_v<It, Other> && std::is_constructible_v<It, Other>>>
    constexpr dense_map_local_iterator(const dense_map_local_iterator<Other> &other) noexcept
        : it{other.it},
          offset{other.offset} {}

    constexpr dense_map_local_iterator &operator++() noexcept {
        return offset = it[offset].next, *this;
    }

    constexpr dense_map_local_iterator operator++(int) noexcept {
        dense_map_local_iterator orig = *this;
        return ++(*this), orig;
    }

    [[nodiscard]] constexpr pointer operator->() const noexcept {
        return operator*();
    }

    [[nodiscard]] constexpr reference operator*() const noexcept {
        return {it[offset].element.first, it[offset].element.second};
    }

    [[nodiscard]] constexpr std::size_t index() const noexcept {
        return offset;
    }

private:
    It it;
    std::size_t offset;
};

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator==(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return lhs.index() == rhs.index();
}

template<typename ILhs, typename IRhs>
[[nodiscard]] constexpr bool operator!=(const dense_map_local_iterator<ILhs> &lhs, const dense_map_local_iterator<IRhs> &rhs) noexcept {
    return !(lhs == rhs);
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Associative container for key-value pairs with unique keys.
 *
 * Internally, elements are organized into buckets. Which bucket an element is
 * placed into depends entirely on the hash of its key. Keys with the same hash
 * code appear in the same bucket.
 *
 * @tparam Key Key type of the associative container.
 * @tparam Type Mapped type of the associative container.
 * @tparam Hash Type of function to use to hash the keys.
 * @tparam KeyEqual Type of function to use to compare the keys for equality.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Key, typename Type, typename Hash, typename KeyEqual, typename Allocator>
class dense_map {
    static constexpr float default_threshold = 0.875f;
    static constexpr std::size_t minimum_capacity = 8u;

    using node_type = internal::dense_map_node<Key, Type>;
    using alloc_traits = typename std::allocator_traits<Allocator>;
    static_assert(std::is_same_v<typename alloc_traits::value_type, std::pair<const Key, Type>>, "Invalid value type");
    using sparse_container_type = std::vector<std::size_t, typename alloc_traits::template rebind_alloc<std::size_t>>;
    using packed_container_type = std::vector<node_type, typename alloc_traits::template rebind_alloc<node_type>>;

    template<typename Other>
    [[nodiscard]] std::size_t key_to_bucket(const Other &key) const noexcept {
        return fast_mod(static_cast<size_type>(sparse.second()(key)), bucket_count());
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) {
        for(auto it = begin(bucket), last = end(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return begin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return end();
    }

    template<typename Other>
    [[nodiscard]] auto constrained_find(const Other &key, std::size_t bucket) const {
        for(auto it = cbegin(bucket), last = cend(bucket); it != last; ++it) {
            if(packed.second()(it->first, key)) {
                return cbegin() + static_cast<typename iterator::difference_type>(it.index());
            }
        }

        return cend();
    }

    template<typename Other, typename... Args>
    [[nodiscard]] auto insert_or_do_nothing(Other &&key, Args &&...args) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::piecewise_construct, std::forward_as_tuple(std::forward<Other>(key)), std::forward_as_tuple(std::forward<Args>(args)...));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    template<typename Other, typename Arg>
    [[nodiscard]] auto insert_or_overwrite(Other &&key, Arg &&value) {
        const auto index = key_to_bucket(key);

        if(auto it = constrained_find(key, index); it != end()) {
            it->second = std::forward<Arg>(value);
            return std::make_pair(it, false);
        }

        packed.first().emplace_back(sparse.first()[index], std::forward<Other>(key), std::forward<Arg>(value));
        sparse.first()[index] = packed.first().size() - 1u;
        rehash_if_required();

        return std::make_pair(--end(), true);
    }

    void move_and_pop(const std::size_t pos) {
        if(const auto last = size() - 1u; pos != last) {
            size_type *curr = sparse.first().data() + key_to_bucket(packed.first().back().element.first);
            packed.first()[pos] = std::move(packed.first().back());
            for(; *curr != last; curr = &packed.first()[*curr].next) {}
            *curr = pos;
        }

        packed.first().pop_back();
    }

    void rehash_if_required() {
        if(size() > (bucket_count() * max_load_factor())) {
            rehash(bucket_count() * 2u);
        }
    }

public:
    /*! @brief Key type of the container. */
    using key_type = Key;
    /*! @brief Mapped type of the container. */
    using mapped_type = Type;
    /*! @brief Key-value type of the container. */
    using value_type = std::pair<const Key, Type>;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Type of function to use to hash the keys. */
    using hasher = Hash;
    /*! @brief Type of function to use to compare the keys for equality. */
    using key_equal = KeyEqual;
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Input iterator type. */
    using iterator = internal::dense_map_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_iterator = internal::dense_map_iterator<typename packed_container_type::const_iterator>;
    /*! @brief Input iterator type. */
    using local_iterator = internal::dense_map_local_iterator<typename packed_container_type::iterator>;
    /*! @brief Constant input iterator type. */
    using const_local_iterator = internal::dense_map_local_iterator<typename packed_container_type::const_iterator>;

    /*! @brief Default constructor. */
    dense_map()
        : dense_map{minimum_capacity} {}

    /**
     * @brief Constructs an empty container with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const allocator_type &allocator)
        : dense_map{minimum_capacity, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator and user
     * supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const allocator_type &allocator)
        : dense_map{cnt, hasher{}, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param allocator The allocator to use.
     */
    dense_map(const size_type cnt, const hasher &hash, const allocator_type &allocator)
        : dense_map{cnt, hash, key_equal{}, allocator} {}

    /**
     * @brief Constructs an empty container with a given allocator, hash
     * function, compare function and user supplied minimal number of buckets.
     * @param cnt Minimal number of buckets.
     * @param hash Hash function to use.
     * @param equal Compare function to use.
     * @param allocator The allocator to use.
     */
    explicit dense_map(const size_type cnt, const hasher &hash = hasher{}, const key_equal &equal = key_equal{}, const allocator_type &allocator = allocator_type{})
        : sparse{allocator, hash},
          packed{allocator, equal},
          threshold{default_threshold} {
        rehash(cnt);
    }

    /*! @brief Default copy constructor. */
    dense_map(const dense_map &) = default;

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    dense_map(const dense_map &other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(other.sparse.first(), allocator), std::forward_as_tuple(other.sparse.second())},
          packed{std::piecewise_construct, std::forward_as_tuple(other.packed.first(), allocator), std::forward_as_tuple(other.packed.second())},
          threshold{other.threshold} {}

    /*! @brief Default move constructor. */
    dense_map(dense_map &&) noexcept(std::is_nothrow_move_constructible_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_constructible_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    dense_map(dense_map &&other, const allocator_type &allocator)
        : sparse{std::piecewise_construct, std::forward_as_tuple(std::move(other.sparse.first()), allocator), std::forward_as_tuple(std::move(other.sparse.second()))},
          packed{std::piecewise_construct, std::forward_as_tuple(std::move(other.packed.first()), allocator), std::forward_as_tuple(std::move(other.packed.second()))},
          threshold{other.threshold} {}

    /**
     * @brief Default copy assignment operator.
     * @return This container.
     */
    dense_map &operator=(const dense_map &) = default;

    /**
     * @brief Default move assignment operator.
     * @return This container.
     */
    dense_map &operator=(dense_map &&) noexcept(std::is_nothrow_move_assignable_v<compressed_pair<sparse_container_type, hasher>> &&std::is_nothrow_move_assignable_v<compressed_pair<packed_container_type, key_equal>>) = default;

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return sparse.first().get_allocator();
    }

    /**
     * @brief Returns an iterator to the beginning.
     *
     * The returned iterator points to the first instance of the internal array.
     * If the array is empty, the returned iterator will be equal to `end()`.
     *
     * @return An iterator to the first instance of the internal array.
     */
    [[nodiscard]] const_iterator cbegin() const noexcept {
        return packed.first().begin();
    }

    /*! @copydoc cbegin */
    [[nodiscard]] const_iterator begin() const noexcept {
        return cbegin();
    }

    /*! @copydoc begin */
    [[nodiscard]] iterator begin() noexcept {
        return packed.first().begin();
    }

    /**
     * @brief Returns an iterator to the end.
     *
     * The returned iterator points to the element following the last instance
     * of the internal array. Attempting to dereference the returned iterator
     * results in undefined behavior.
     *
     * @return An iterator to the element following the last instance of the
     * internal array.
     */
    [[nodiscard]] const_iterator cend() const noexcept {
        return packed.first().end();
    }

    /*! @copydoc cend */
    [[nodiscard]] const_iterator end() const noexcept {
        return cend();
    }

    /*! @copydoc end */
    [[nodiscard]] iterator end() noexcept {
        return packed.first().end();
    }

    /**
     * @brief Checks whether a container is empty.
     * @return True if the container is empty, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return packed.first().empty();
    }

    /**
     * @brief Returns the number of elements in a container.
     * @return Number of elements in a container.
     */
    [[nodiscard]] size_type size() const noexcept {
        return packed.first().size();
    }

    /**
     * @brief Returns the maximum possible number of elements.
     * @return Maximum possible number of elements.
     */
    [[nodiscard]] size_type max_size() const noexcept {
        return packed.first().max_size();
    }

    /*! @brief Clears the container. */
    void clear() noexcept {
        sparse.first().clear();
        packed.first().clear();
        rehash(0u);
    }

    /**
     * @brief Inserts an element into the container, if the key does not exist.
     * @param value A key-value pair eventually convertible to the value type.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    std::pair<iterator, bool> insert(const value_type &value) {
        return insert_or_do_nothing(value.first, value.second);
    }

    /*! @copydoc insert */
    std::pair<iterator, bool> insert(value_type &&value) {
        return insert_or_do_nothing(std::move(value.first), std::move(value.second));
    }

    /**
     * @copydoc insert
     * @tparam Arg Type of the key-value pair to insert into the container.
     */
    template<typename Arg>
    std::enable_if_t<std::is_constructible_v<value_type, Arg &&>, std::pair<iterator, bool>>
    insert(Arg &&value) {
        return insert_or_do_nothing(std::forward<Arg>(value).first, std::forward<Arg>(value).second);
    }

    /**
     * @brief Inserts elements into the container, if their keys do not exist.
     * @tparam It Type of input iterator.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     */
    template<typename It>
    void insert(It first, It last) {
        for(; first != last; ++first) {
            insert(*first);
        }
    }

    /**
     * @brief Inserts an element into the container or assigns to the current
     * element if the key already exists.
     * @tparam Arg Type of the value to insert or assign.
     * @param key A key used both to look up and to insert if not found.
     * @param value A value to insert or assign.
     * @return A pair consisting of an iterator to the element and a bool
     * denoting whether the insertion took place.
     */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(const key_type &key, Arg &&value) {
        return insert_or_overwrite(key, std::forward<Arg>(value));
    }

    /*! @copydoc insert_or_assign */
    template<typename Arg>
    std::pair<iterator, bool> insert_or_assign(key_type &&key, Arg &&value) {
        return insert_or_overwrite(std::move(key), std::forward<Arg>(value));
    }

    /**
     * @brief Constructs an element in-place, if the key does not exist.
     *
     * The element is also constructed when the container already has the key,
     * in which case the newly constructed object is destroyed immediately.
     *
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> emplace([[maybe_unused]] Args &&...args) {
        if constexpr(sizeof...(Args) == 0u) {
            return insert_or_do_nothing(key_type{});
        } else if constexpr(sizeof...(Args) == 1u) {
            return insert_or_do_nothing(std::forward<Args>(args).first..., std::forward<Args>(args).second...);
        } else if constexpr(sizeof...(Args) == 2u) {
            return insert_or_do_nothing(std::forward<Args>(args)...);
        } else {
            auto &node = packed.first().emplace_back(packed.first().size(), std::forward<Args>(args)...);
            const auto index = key_to_bucket(node.element.first);

            if(auto it = constrained_find(node.element.first, index); it != end()) {
                packed.first().pop_back();
                return std::make_pair(it, false);
            }

            std::swap(node.next, sparse.first()[index]);
            rehash_if_required();

            return std::make_pair(--end(), true);
        }
    }

    /**
     * @brief Inserts in-place if the key does not exist, does nothing if the
     * key exists.
     * @tparam Args Types of arguments to forward to the constructor of the
     * element.
     * @param key A key used both to look up and to insert if not found.
     * @param args Arguments to forward to the constructor of the element.
     * @return A pair consisting of an iterator to the inserted element (or to
     * the element that prevented the insertion) and a bool denoting whether the
     * insertion took place.
     */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(const key_type &key, Args &&...args) {
        return insert_or_do_nothing(key, std::forward<Args>(args)...);
    }

    /*! @copydoc try_emplace */
    template<typename... Args>
    std::pair<iterator, bool> try_emplace(key_type &&key, Args &&...args) {
        return insert_or_do_nothing(std::move(key), std::forward<Args>(args)...);
    }

    /**
     * @brief Removes an element from a given position.
     * @param pos An iterator to the element to remove.
     * @return An iterator following the removed element.
     */
    iterator erase(const_iterator pos) {
        const auto diff = pos - cbegin();
        erase(pos->first);
        return begin() + diff;
    }

    /**
     * @brief Removes the given elements from a container.
     * @param first An iterator to the first element of the range of elements.
     * @param last An iterator past the last element of the range of elements.
     * @return An iterator following the last removed element.
     */
    iterator erase(const_iterator first, const_iterator last) {
        const auto dist = first - cbegin();

        for(auto from = last - cbegin(); from != dist; --from) {
            erase(packed.first()[from - 1u].element.first);
        }

        return (begin() + dist);
    }

    /**
     * @brief Removes the element associated with a given key.
     * @param key A key value of an element to remove.
     * @return Number of elements removed (either 0 or 1).
     */
    size_type erase(const key_type &key) {
        for(size_type *curr = sparse.first().data() + key_to_bucket(key); *curr != (std::numeric_limits<size_type>::max)(); curr = &packed.first()[*curr].next) {
            if(packed.second()(packed.first()[*curr].element.first, key)) {
                const auto index = *curr;
                *curr = packed.first()[*curr].next;
                move_and_pop(index);
                return 1u;
            }
        }

        return 0u;
    }

    /**
     * @brief Exchanges the contents with those of a given container.
     * @param other Container to exchange the content with.
     */
    void swap(dense_map &other) {
        using std::swap;
        swap(sparse, other.sparse);
        swap(packed, other.packed);
        swap(threshold, other.threshold);
    }

    /**
     * @brief Accesses a given element with bounds checking.
     * @param key A key of an element to find.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &at(const key_type &key) {
        auto it = find(key);
        ENTT_ASSERT(it != end(), "Invalid key");
        return it->second;
    }

    /*! @copydoc at */
    [[nodiscard]] const mapped_type &at(const key_type &key) const {
        auto it = find(key);
        ENTT_ASSERT(it != cend(), "Invalid key");
        return it->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](const key_type &key) {
        return insert_or_do_nothing(key).first->second;
    }

    /**
     * @brief Accesses or inserts a given element.
     * @param key A key of an element to find or insert.
     * @return A reference to the mapped value of the requested element.
     */
    [[nodiscard]] mapped_type &operator[](key_type &&key) {
        return insert_or_do_nothing(std::move(key)).first->second;
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    [[nodiscard]] size_type count(const key_type &key) const {
        return find(key) != end();
    }

    /**
     * @brief Returns the number of elements matching a key (either 1 or 0).
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return Number of elements matching the key (either 1 or 0).
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, size_type>>
    count(const Other &key) const {
        return find(key) != end();
    }

    /**
     * @brief Finds an element with a given key.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    [[nodiscard]] iterator find(const key_type &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    [[nodiscard]] const_iterator find(const key_type &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Finds an element with a key that compares _equivalent_ to a given
     * key.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return An iterator to an element with the given key. If no such element
     * is found, a past-the-end iterator is returned.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, iterator>>
    find(const Other &key) {
        return constrained_find(key, key_to_bucket(key));
    }

    /*! @copydoc find */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, const_iterator>>
    find(const Other &key) const {
        return constrained_find(key, key_to_bucket(key));
    }

    /**
     * @brief Returns a range containing all elements with a given key.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    [[nodiscard]] std::pair<iterator, iterator> equal_range(const key_type &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    [[nodiscard]] std::pair<const_iterator, const_iterator> equal_range(const key_type &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Returns a range containing all elements that compare _equivalent_
     * to a given key.
     * @tparam Other Type of an element to search for.
     * @param key Key value of an element to search for.
     * @return A pair of iterators pointing to the first element and past the
     * last element of the range.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<iterator, iterator>>>
    equal_range(const Other &key) {
        const auto it = find(key);
        return {it, it + !(it == end())};
    }

    /*! @copydoc equal_range */
    template<class Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, std::pair<const_iterator, const_iterator>>>
    equal_range(const Other &key) const {
        const auto it = find(key);
        return {it, it + !(it == cend())};
    }

    /**
     * @brief Checks if the container contains an element with a given key.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    [[nodiscard]] bool contains(const key_type &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Checks if the container contains an element with a key that
     * compares _equivalent_ to a given value.
     * @tparam Other Type of the key value of an element to search for.
     * @param key Key value of an element to search for.
     * @return True if there is such an element, false otherwise.
     */
    template<typename Other>
    [[nodiscard]] std::enable_if_t<is_transparent_v<hasher> && is_transparent_v<key_equal>, std::conditional_t<false, Other, bool>>
    contains(const Other &key) const {
        return (find(key) != cend());
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator cbegin(const size_type index) const {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] const_local_iterator begin(const size_type index) const {
        return cbegin(index);
    }

    /**
     * @brief Returns an iterator to the beginning of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the beginning of the given bucket.
     */
    [[nodiscard]] local_iterator begin(const size_type index) {
        return {packed.first().begin(), sparse.first()[index]};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator cend([[maybe_unused]] const size_type index) const {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] const_local_iterator end(const size_type index) const {
        return cend(index);
    }

    /**
     * @brief Returns an iterator to the end of a given bucket.
     * @param index An index of a bucket to access.
     * @return An iterator to the end of the given bucket.
     */
    [[nodiscard]] local_iterator end([[maybe_unused]] const size_type index) {
        return {packed.first().begin(), (std::numeric_limits<size_type>::max)()};
    }

    /**
     * @brief Returns the number of buckets.
     * @return The number of buckets.
     */
    [[nodiscard]] size_type bucket_count() const {
        return sparse.first().size();
    }

    /**
     * @brief Returns the maximum number of buckets.
     * @return The maximum number of buckets.
     */
    [[nodiscard]] size_type max_bucket_count() const {
        return sparse.first().max_size();
    }

    /**
     * @brief Returns the number of elements in a given bucket.
     * @param index The index of the bucket to examine.
     * @return The number of elements in the given bucket.
     */
    [[nodiscard]] size_type bucket_size(const size_type index) const {
        return static_cast<size_type>(std::distance(begin(index), end(index)));
    }

    /**
     * @brief Returns the bucket for a given key.
     * @param key The value of the key to examine.
     * @return The bucket for the given key.
     */
    [[nodiscard]] size_type bucket(const key_type &key) const {
        return key_to_bucket(key);
    }

    /**
     * @brief Returns the average number of elements per bucket.
     * @return The average number of elements per bucket.
     */
    [[nodiscard]] float load_factor() const {
        return size() / static_cast<float>(bucket_count());
    }

    /**
     * @brief Returns the maximum average number of elements per bucket.
     * @return The maximum average number of elements per bucket.
     */
    [[nodiscard]] float max_load_factor() const {
        return threshold;
    }

    /**
     * @brief Sets the desired maximum average number of elements per bucket.
     * @param value A desired maximum average number of elements per bucket.
     */
    void max_load_factor(const float value) {
        ENTT_ASSERT(value > 0.f, "Invalid load factor");
        threshold = value;
        rehash(0u);
    }

    /**
     * @brief Reserves at least the specified number of buckets and regenerates
     * the hash table.
     * @param cnt New number of buckets.
     */
    void rehash(const size_type cnt) {
        auto value = cnt > minimum_capacity ? cnt : minimum_capacity;
        const auto cap = static_cast<size_type>(size() / max_load_factor());
        value = value > cap ? value : cap;

        if(const auto sz = next_power_of_two(value); sz != bucket_count()) {
            sparse.first().resize(sz);

            for(auto &&elem: sparse.first()) {
                elem = std::numeric_limits<size_type>::max();
            }

            for(size_type pos{}, last = size(); pos < last; ++pos) {
                const auto index = key_to_bucket(packed.first()[pos].element.first);
                packed.first()[pos].next = std::exchange(sparse.first()[index], pos);
            }
        }
    }

    /**
     * @brief Reserves space for at least the specified number of elements and
     * regenerates the hash table.
     * @param cnt New number of elements.
     */
    void reserve(const size_type cnt) {
        packed.first().reserve(cnt);
        rehash(static_cast<size_type>(std::ceil(cnt / max_load_factor())));
    }

    /**
     * @brief Returns the function used to hash the keys.
     * @return The function used to hash the keys.
     */
    [[nodiscard]] hasher hash_function() const {
        return sparse.second();
    }

    /**
     * @brief Returns the function used to compare keys for equality.
     * @return The function used to compare keys for equality.
     */
    [[nodiscard]] key_equal key_eq() const {
        return packed.second();
    }

private:
    compressed_pair<sparse_container_type, hasher> sparse;
    compressed_pair<packed_container_type, key_equal> packed;
    float threshold;
};

} // namespace entt

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace std {

template<typename Key, typename Value, typename Allocator>
struct uses_allocator<entt::internal::dense_map_node<Key, Value>, Allocator>
    : std::true_type {};

} // namespace std

/**
 * Internal details not to be documented.
 * @endcond
 */

#endif

// #include "../core/compressed_pair.hpp"
#ifndef ENTT_CORE_COMPRESSED_PAIR_HPP
#define ENTT_CORE_COMPRESSED_PAIR_HPP

#include <cstddef>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "type_traits.hpp"
#ifndef ENTT_CORE_TYPE_TRAITS_HPP
#define ENTT_CORE_TYPE_TRAITS_HPP

#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Utility class to disambiguate overloaded functions.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
struct choice_t
    // Unfortunately, doxygen cannot parse such a construct.
    : /*! @cond TURN_OFF_DOXYGEN */ choice_t<N - 1> /*! @endcond */
{};

/*! @copybrief choice_t */
template<>
struct choice_t<0> {};

/**
 * @brief Variable template for the choice trick.
 * @tparam N Number of choices available.
 */
template<std::size_t N>
inline constexpr choice_t<N> choice{};

/**
 * @brief Identity type trait.
 *
 * Useful to establish non-deduced contexts in template argument deduction
 * (waiting for C++20) or to provide types through function arguments.
 *
 * @tparam Type A type.
 */
template<typename Type>
struct type_identity {
    /*! @brief Identity type. */
    using type = Type;
};

/**
 * @brief Helper type.
 * @tparam Type A type.
 */
template<typename Type>
using type_identity_t = typename type_identity<Type>::type;

/**
 * @brief A type-only `sizeof` wrapper that returns 0 where `sizeof` complains.
 * @tparam Type The type of which to return the size.
 * @tparam The size of the type if `sizeof` accepts it, 0 otherwise.
 */
template<typename Type, typename = void>
struct size_of: std::integral_constant<std::size_t, 0u> {};

/*! @copydoc size_of */
template<typename Type>
struct size_of<Type, std::void_t<decltype(sizeof(Type))>>
    : std::integral_constant<std::size_t, sizeof(Type)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type of which to return the size.
 */
template<typename Type>
inline constexpr std::size_t size_of_v = size_of<Type>::value;

/**
 * @brief Using declaration to be used to _repeat_ the same type a number of
 * times equal to the size of a given parameter pack.
 * @tparam Type A type to repeat.
 */
template<typename Type, typename>
using unpack_as_type = Type;

/**
 * @brief Helper variable template to be used to _repeat_ the same value a
 * number of times equal to the size of a given parameter pack.
 * @tparam Value A value to repeat.
 */
template<auto Value, typename>
inline constexpr auto unpack_as_value = Value;

/**
 * @brief Wraps a static constant.
 * @tparam Value A static constant.
 */
template<auto Value>
using integral_constant = std::integral_constant<decltype(Value), Value>;

/**
 * @brief Alias template to facilitate the creation of named values.
 * @tparam Value A constant value at least convertible to `id_type`.
 */
template<id_type Value>
using tag = integral_constant<Value>;

/**
 * @brief A class to use to push around lists of types, nothing more.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list {
    /*! @brief Type list type. */
    using type = type_list;
    /*! @brief Compile-time number of elements in the type list. */
    static constexpr auto size = sizeof...(Type);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct type_list_element;

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Index Index of the type to return.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
    : type_list_element<Index - 1u, type_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
    /*! @brief Searched type. */
    using type = First;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the type to return.
 * @tparam List Type list to search into.
 */
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam First First type provided by the type list.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 * @tparam Other Other types provided by the type list.
 */
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
    static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Provides compile-time type access to the types of a type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type>
struct type_list_index<Type, type_list<>> {
    /*! @brief Unsigned integer type. */
    using value_type = std::size_t;
    /*! @brief Compile-time position of the given type in the sublist. */
    static constexpr value_type value = 0u;
};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for and for which to return the index.
 */
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @return A type list composed by the types of both the type lists.
 */
template<typename... Type, typename... Other>
constexpr type_list<Type..., Other...> operator+(type_list<Type...>, type_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_cat;

/*! @brief Concatenates multiple type lists. */
template<>
struct type_list_cat<> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<>;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 * @tparam List Other type lists, if any.
 */
template<typename... Type, typename... Other, typename... List>
struct type_list_cat<type_list<Type...>, type_list<Other...>, List...> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = typename type_list_cat<type_list<Type..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple type lists.
 * @tparam Type Types provided by the type list.
 */
template<typename... Type>
struct type_list_cat<type_list<Type...>> {
    /*! @brief A type list composed by the types of all the type lists. */
    using type = type_list<Type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists to concatenate.
 */
template<typename... List>
using type_list_cat_t = typename type_list_cat<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename>
struct type_list_unique;

/**
 * @brief Removes duplicates types from a type list.
 * @tparam Type One of the types provided by the given type list.
 * @tparam Other The other types provided by the given type list.
 */
template<typename Type, typename... Other>
struct type_list_unique<type_list<Type, Other...>> {
    /*! @brief A type list without duplicate types. */
    using type = std::conditional_t<
        (std::is_same_v<Type, Other> || ...),
        typename type_list_unique<type_list<Other...>>::type,
        type_list_cat_t<type_list<Type>, typename type_list_unique<type_list<Other...>>::type>>;
};

/*! @brief Removes duplicates types from a type list. */
template<>
struct type_list_unique<type_list<>> {
    /*! @brief A type list without duplicate types. */
    using type = type_list<>;
};

/**
 * @brief Helper type.
 * @tparam Type A type list.
 */
template<typename Type>
using type_list_unique_t = typename type_list_unique<Type>::type;

/**
 * @brief Provides the member constant `value` to true if a type list contains a
 * given type, false otherwise.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
struct type_list_contains;

/**
 * @copybrief type_list_contains
 * @tparam Type Types provided by the type list.
 * @tparam Other Type to look for.
 */
template<typename... Type, typename Other>
struct type_list_contains<type_list<Type...>, Other>: std::disjunction<std::is_same<Type, Other>...> {};

/**
 * @brief Helper variable template.
 * @tparam List Type list.
 * @tparam Type Type to look for.
 */
template<typename List, typename Type>
inline constexpr bool type_list_contains_v = type_list_contains<List, Type>::value;

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct type_list_diff;

/**
 * @brief Computes the difference between two type lists.
 * @tparam Type Types provided by the first type list.
 * @tparam Other Types provided by the second type list.
 */
template<typename... Type, typename... Other>
struct type_list_diff<type_list<Type...>, type_list<Other...>> {
    /*! @brief A type list that is the difference between the two type lists. */
    using type = type_list_cat_t<std::conditional_t<type_list_contains_v<type_list<Other...>, Type>, type_list<>, type_list<Type>>...>;
};

/**
 * @brief Helper type.
 * @tparam List Type lists between which to compute the difference.
 */
template<typename... List>
using type_list_diff_t = typename type_list_diff<List...>::type;

/*! @brief Primary template isn't defined on purpose. */
template<typename, template<typename...> class>
struct type_list_transform;

/**
 * @brief Applies a given _function_ to a type list and generate a new list.
 * @tparam Type Types provided by the type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename... Type, template<typename...> class Op>
struct type_list_transform<type_list<Type...>, Op> {
    /*! @brief Resulting type list after applying the transform function. */
    using type = type_list<typename Op<Type>::type...>;
};

/**
 * @brief Helper type.
 * @tparam List Type list.
 * @tparam Op Unary operation as template class with a type member named `type`.
 */
template<typename List, template<typename...> class Op>
using type_list_transform_t = typename type_list_transform<List, Op>::type;

/**
 * @brief A class to use to push around lists of constant values, nothing more.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list {
    /*! @brief Value list type. */
    using type = value_list;
    /*! @brief Compile-time number of elements in the value list. */
    static constexpr auto size = sizeof...(Value);
};

/*! @brief Primary template isn't defined on purpose. */
template<std::size_t, typename>
struct value_list_element;

/**
 * @brief Provides compile-time indexed access to the values of a value list.
 * @tparam Index Index of the value to return.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<std::size_t Index, auto Value, auto... Other>
struct value_list_element<Index, value_list<Value, Other...>>
    : value_list_element<Index - 1u, value_list<Other...>> {};

/**
 * @brief Provides compile-time indexed access to the types of a type list.
 * @tparam Value First value provided by the value list.
 * @tparam Other Other values provided by the value list.
 */
template<auto Value, auto... Other>
struct value_list_element<0u, value_list<Value, Other...>> {
    /*! @brief Searched value. */
    static constexpr auto value = Value;
};

/**
 * @brief Helper type.
 * @tparam Index Index of the value to return.
 * @tparam List Value list to search into.
 */
template<std::size_t Index, typename List>
inline constexpr auto value_list_element_v = value_list_element<Index, List>::value;

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @return A value list composed by the values of both the value lists.
 */
template<auto... Value, auto... Other>
constexpr value_list<Value..., Other...> operator+(value_list<Value...>, value_list<Other...>) {
    return {};
}

/*! @brief Primary template isn't defined on purpose. */
template<typename...>
struct value_list_cat;

/*! @brief Concatenates multiple value lists. */
template<>
struct value_list_cat<> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<>;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the first value list.
 * @tparam Other Values provided by the second value list.
 * @tparam List Other value lists, if any.
 */
template<auto... Value, auto... Other, typename... List>
struct value_list_cat<value_list<Value...>, value_list<Other...>, List...> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = typename value_list_cat<value_list<Value..., Other...>, List...>::type;
};

/**
 * @brief Concatenates multiple value lists.
 * @tparam Value Values provided by the value list.
 */
template<auto... Value>
struct value_list_cat<value_list<Value...>> {
    /*! @brief A value list composed by the values of all the value lists. */
    using type = value_list<Value...>;
};

/**
 * @brief Helper type.
 * @tparam List Value lists to concatenate.
 */
template<typename... List>
using value_list_cat_t = typename value_list_cat<List...>::type;

/*! @brief Same as std::is_invocable, but with tuples. */
template<typename, typename>
struct is_applicable: std::false_type {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @copybrief is_applicable
 * @tparam Func A valid function type.
 * @tparam Tuple Tuple-like type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, template<typename...> class Tuple, typename... Args>
struct is_applicable<Func, const Tuple<Args...>>: std::is_invocable<Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Func, typename Args>
inline constexpr bool is_applicable_v = is_applicable<Func, Args>::value;

/*! @brief Same as std::is_invocable_r, but with tuples for arguments. */
template<typename, typename, typename>
struct is_applicable_r: std::false_type {};

/**
 * @copybrief is_applicable_r
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename... Args>
struct is_applicable_r<Ret, Func, std::tuple<Args...>>: std::is_invocable_r<Ret, Func, Args...> {};

/**
 * @brief Helper variable template.
 * @tparam Ret The type to which the return type of the function should be
 * convertible.
 * @tparam Func A valid function type.
 * @tparam Args The list of arguments to use to probe the function type.
 */
template<typename Ret, typename Func, typename Args>
inline constexpr bool is_applicable_r_v = is_applicable_r<Ret, Func, Args>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * complete, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_complete: std::false_type {};

/*! @copydoc is_complete */
template<typename Type>
struct is_complete<Type, std::void_t<decltype(sizeof(Type))>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_complete_v = is_complete<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is an
 * iterator, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_iterator: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_iterator_category: std::false_type {};

template<typename Type>
struct has_iterator_category<Type, std::void_t<typename std::iterator_traits<Type>::iterator_category>>: std::true_type {};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_iterator */
template<typename Type>
struct is_iterator<Type, std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_pointer_t<Type>>, void>>>
    : internal::has_iterator_category<Type> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_iterator_v = is_iterator<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is both
 * an empty and non-final class, false otherwise.
 * @tparam Type The type to test
 */
template<typename Type>
struct is_ebco_eligible
    : std::conjunction<std::is_empty<Type>, std::negation<std::is_final<Type>>> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_ebco_eligible_v = is_ebco_eligible<Type>::value;

/**
 * @brief Provides the member constant `value` to true if `Type::is_transparent`
 * is valid and denotes a type, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_transparent: std::false_type {};

/*! @copydoc is_transparent */
template<typename Type>
struct is_transparent<Type, std::void_t<typename Type::is_transparent>>: std::true_type {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_transparent_v = is_transparent<Type>::value;

/**
 * @brief Provides the member constant `value` to true if a given type is
 * equality comparable, false otherwise.
 * @tparam Type The type to test.
 */
template<typename Type, typename = void>
struct is_equality_comparable: std::false_type {};

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename, typename = void>
struct has_tuple_size_value: std::false_type {};

template<typename Type>
struct has_tuple_size_value<Type, std::void_t<decltype(std::tuple_size<const Type>::value)>>: std::true_type {};

template<typename Type, std::size_t... Index>
[[nodiscard]] constexpr bool unpack_maybe_equality_comparable(std::index_sequence<Index...>) {
    return (is_equality_comparable<std::tuple_element_t<Index, Type>>::value && ...);
}

template<typename>
[[nodiscard]] constexpr bool maybe_equality_comparable(choice_t<0>) {
    return true;
}

template<typename Type>
[[nodiscard]] constexpr auto maybe_equality_comparable(choice_t<1>) -> decltype(std::declval<typename Type::value_type>(), bool{}) {
    if constexpr(is_iterator_v<Type>) {
        return true;
    } else if constexpr(std::is_same_v<typename Type::value_type, Type>) {
        return maybe_equality_comparable<Type>(choice<0>);
    } else {
        return is_equality_comparable<typename Type::value_type>::value;
    }
}

template<typename Type>
[[nodiscard]] constexpr std::enable_if_t<is_complete_v<std::tuple_size<std::remove_cv_t<Type>>>, bool> maybe_equality_comparable(choice_t<2>) {
    if constexpr(has_tuple_size_value<Type>::value) {
        return unpack_maybe_equality_comparable<Type>(std::make_index_sequence<std::tuple_size<Type>::value>{});
    } else {
        return maybe_equality_comparable<Type>(choice<1>);
    }
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/*! @copydoc is_equality_comparable */
template<typename Type>
struct is_equality_comparable<Type, std::void_t<decltype(std::declval<Type>() == std::declval<Type>())>>
    : std::bool_constant<internal::maybe_equality_comparable<Type>(choice<2>)> {};

/**
 * @brief Helper variable template.
 * @tparam Type The type to test.
 */
template<typename Type>
inline constexpr bool is_equality_comparable_v = is_equality_comparable<Type>::value;

/**
 * @brief Transcribes the constness of a type to another type.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
struct constness_as {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = std::remove_const_t<To>;
};

/*! @copydoc constness_as */
template<typename To, typename From>
struct constness_as<To, const From> {
    /*! @brief The type resulting from the transcription of the constness. */
    using type = const To;
};

/**
 * @brief Alias template to facilitate the transcription of the constness.
 * @tparam To The type to which to transcribe the constness.
 * @tparam From The type from which to transcribe the constness.
 */
template<typename To, typename From>
using constness_as_t = typename constness_as<To, From>::type;

/**
 * @brief Extracts the class of a non-static member object or function.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
class member_class {
    static_assert(std::is_member_pointer_v<Member>, "Invalid pointer type to non-static member object or function");

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...));

    template<typename Class, typename Ret, typename... Args>
    static Class *clazz(Ret (Class::*)(Args...) const);

    template<typename Class, typename Type>
    static Class *clazz(Type Class::*);

public:
    /*! @brief The class of the given non-static member object or function. */
    using type = std::remove_pointer_t<decltype(clazz(std::declval<Member>()))>;
};

/**
 * @brief Helper type.
 * @tparam Member A pointer to a non-static member object or function.
 */
template<typename Member>
using member_class_t = typename member_class<Member>::type;

/**
 * @brief Extracts the n-th argument of a given function or member function.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
class nth_argument {
    template<typename Ret, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...));

    template<typename Ret, typename Class, typename... Args>
    static constexpr type_list<Args...> pick_up(Ret (Class ::*)(Args...) const);

    template<typename Type, typename Class>
    static constexpr type_list<Type> pick_up(Type Class ::*);

public:
    /*! @brief N-th argument of the given function or member function. */
    using type = type_list_element_t<Index, decltype(pick_up(Candidate))>;
};

/**
 * @brief Helper type.
 * @tparam Index The index of the argument to extract.
 * @tparam Candidate A valid function, member function or data member.
 */
template<std::size_t Index, auto Candidate>
using nth_argument_t = typename nth_argument<Index, Candidate>::type;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Type, std::size_t, typename = void>
struct compressed_pair_element {
    using reference = Type &;
    using const_reference = const Type &;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>)
        : value{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
        : value{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<Type, Args...>)
        : value{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return value;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return value;
    }

private:
    Type value;
};

template<typename Type, std::size_t Tag>
struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Type>>>: Type {
    using reference = Type &;
    using const_reference = const Type &;
    using base_type = Type;

    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
        : base_type{} {}

    template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
    constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)
        : base_type{std::forward<Arg>(arg)} {}

    template<typename... Args, std::size_t... Index>
    constexpr compressed_pair_element(std::tuple<Args...> args, std::index_sequence<Index...>) noexcept(std::is_nothrow_constructible_v<base_type, Args...>)
        : base_type{std::forward<Args>(std::get<Index>(args))...} {}

    [[nodiscard]] constexpr reference get() noexcept {
        return *this;
    }

    [[nodiscard]] constexpr const_reference get() const noexcept {
        return *this;
    }
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief A compressed pair.
 *
 * A pair that exploits the _Empty Base Class Optimization_ (or _EBCO_) to
 * reduce its final size to a minimum.
 *
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
class compressed_pair final
    : internal::compressed_pair_element<First, 0u>,
      internal::compressed_pair_element<Second, 1u> {
    using first_base = internal::compressed_pair_element<First, 0u>;
    using second_base = internal::compressed_pair_element<Second, 1u>;

public:
    /*! @brief The type of the first element that the pair stores. */
    using first_type = First;
    /*! @brief The type of the second element that the pair stores. */
    using second_type = Second;

    /**
     * @brief Default constructor, conditionally enabled.
     *
     * This constructor is only available when the types that the pair stores
     * are both at least default constructible.
     *
     * @tparam Dummy Dummy template parameter used for internal purposes.
     */
    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<first_type> && std::is_default_constructible_v<second_type>>>
    constexpr compressed_pair() noexcept(std::is_nothrow_default_constructible_v<first_base> &&std::is_nothrow_default_constructible_v<second_base>)
        : first_base{},
          second_base{} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    constexpr compressed_pair(const compressed_pair &other) noexcept(std::is_nothrow_copy_constructible_v<first_base> &&std::is_nothrow_copy_constructible_v<second_base>) = default;

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    constexpr compressed_pair(compressed_pair &&other) noexcept(std::is_nothrow_move_constructible_v<first_base> &&std::is_nothrow_move_constructible_v<second_base>) = default;

    /**
     * @brief Constructs a pair from its values.
     * @tparam Arg Type of value to use to initialize the first element.
     * @tparam Other Type of value to use to initialize the second element.
     * @param arg Value to use to initialize the first element.
     * @param other Value to use to initialize the second element.
     */
    template<typename Arg, typename Other>
    constexpr compressed_pair(Arg &&arg, Other &&other) noexcept(std::is_nothrow_constructible_v<first_base, Arg> &&std::is_nothrow_constructible_v<second_base, Other>)
        : first_base{std::forward<Arg>(arg)},
          second_base{std::forward<Other>(other)} {}

    /**
     * @brief Constructs a pair by forwarding the arguments to its parts.
     * @tparam Args Types of arguments to use to initialize the first element.
     * @tparam Other Types of arguments to use to initialize the second element.
     * @param args Arguments to use to initialize the first element.
     * @param other Arguments to use to initialize the second element.
     */
    template<typename... Args, typename... Other>
    constexpr compressed_pair(std::piecewise_construct_t, std::tuple<Args...> args, std::tuple<Other...> other) noexcept(std::is_nothrow_constructible_v<first_base, Args...> &&std::is_nothrow_constructible_v<second_base, Other...>)
        : first_base{std::move(args), std::index_sequence_for<Args...>{}},
          second_base{std::move(other), std::index_sequence_for<Other...>{}} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(const compressed_pair &other) noexcept(std::is_nothrow_copy_assignable_v<first_base> &&std::is_nothrow_copy_assignable_v<second_base>) = default;

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This compressed pair object.
     */
    constexpr compressed_pair &operator=(compressed_pair &&other) noexcept(std::is_nothrow_move_assignable_v<first_base> &&std::is_nothrow_move_assignable_v<second_base>) = default;

    /**
     * @brief Returns the first element that a pair stores.
     * @return The first element that a pair stores.
     */
    [[nodiscard]] constexpr first_type &first() noexcept {
        return static_cast<first_base &>(*this).get();
    }

    /*! @copydoc first */
    [[nodiscard]] constexpr const first_type &first() const noexcept {
        return static_cast<const first_base &>(*this).get();
    }

    /**
     * @brief Returns the second element that a pair stores.
     * @return The second element that a pair stores.
     */
    [[nodiscard]] constexpr second_type &second() noexcept {
        return static_cast<second_base &>(*this).get();
    }

    /*! @copydoc second */
    [[nodiscard]] constexpr const second_type &second() const noexcept {
        return static_cast<const second_base &>(*this).get();
    }

    /**
     * @brief Swaps two compressed pair objects.
     * @param other The compressed pair to swap with.
     */
    constexpr void swap(compressed_pair &other) noexcept(std::is_nothrow_swappable_v<first_type> &&std::is_nothrow_swappable_v<second_type>) {
        using std::swap;
        swap(first(), other.first());
        swap(second(), other.second());
    }

    /**
     * @brief Extracts an element from the compressed pair.
     * @tparam Index An integer value that is either 0 or 1.
     * @return Returns a reference to the first element if `Index` is 0 and a
     * reference to the second element if `Index` is 1.
     */
    template<std::size_t Index>
    constexpr decltype(auto) get() noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }

    /*! @copydoc get */
    template<std::size_t Index>
    constexpr decltype(auto) get() const noexcept {
        if constexpr(Index == 0u) {
            return first();
        } else {
            static_assert(Index == 1u, "Index out of bounds");
            return second();
        }
    }
};

/**
 * @brief Deduction guide.
 * @tparam Type Type of value to use to initialize the first element.
 * @tparam Other Type of value to use to initialize the second element.
 */
template<typename Type, typename Other>
compressed_pair(Type &&, Other &&) -> compressed_pair<std::decay_t<Type>, std::decay_t<Other>>;

/**
 * @brief Swaps two compressed pair objects.
 * @tparam First The type of the first element that the pairs store.
 * @tparam Second The type of the second element that the pairs store.
 * @param lhs A valid compressed pair object.
 * @param rhs A valid compressed pair object.
 */
template<typename First, typename Second>
inline constexpr void swap(compressed_pair<First, Second> &lhs, compressed_pair<First, Second> &rhs) {
    lhs.swap(rhs);
}

} // namespace entt

// disable structured binding support for clang 6, it messes when specializing tuple_size
#if !defined __clang_major__ || __clang_major__ > 6
namespace std {

/**
 * @brief `std::tuple_size` specialization for `compressed_pair`s.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<typename First, typename Second>
struct tuple_size<entt::compressed_pair<First, Second>>: integral_constant<size_t, 2u> {};

/**
 * @brief `std::tuple_element` specialization for `compressed_pair`s.
 * @tparam Index The index of the type to return.
 * @tparam First The type of the first element that the pair stores.
 * @tparam Second The type of the second element that the pair stores.
 */
template<size_t Index, typename First, typename Second>
struct tuple_element<Index, entt::compressed_pair<First, Second>>: conditional<Index == 0u, First, Second> {
    static_assert(Index < 2u, "Index out of bounds");
};

} // namespace std
#endif

#endif

// #include "../core/fwd.hpp"
#ifndef ENTT_CORE_FWD_HPP
#define ENTT_CORE_FWD_HPP

#include <cstddef>
// #include "../config/config.h"


namespace entt {

template<std::size_t Len = sizeof(double[2]), std::size_t = alignof(double[2])>
class basic_any;

/*! @brief Alias declaration for type identifiers. */
using id_type = ENTT_ID_TYPE;

/*! @brief Alias declaration for the most common use case. */
using any = basic_any<>;

} // namespace entt

#endif

// #include "../core/type_info.hpp"
#ifndef ENTT_CORE_TYPE_INFO_HPP
#define ENTT_CORE_TYPE_INFO_HPP

#include <string_view>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/attribute.h"
#ifndef ENTT_CORE_ATTRIBUTE_H
#define ENTT_CORE_ATTRIBUTE_H

#ifndef ENTT_EXPORT
#    if defined _WIN32 || defined __CYGWIN__ || defined _MSC_VER
#        define ENTT_EXPORT __declspec(dllexport)
#        define ENTT_IMPORT __declspec(dllimport)
#        define ENTT_HIDDEN
#    elif defined __GNUC__ && __GNUC__ >= 4
#        define ENTT_EXPORT __attribute__((visibility("default")))
#        define ENTT_IMPORT __attribute__((visibility("default")))
#        define ENTT_HIDDEN __attribute__((visibility("hidden")))
#    else /* Unsupported compiler */
#        define ENTT_EXPORT
#        define ENTT_IMPORT
#        define ENTT_HIDDEN
#    endif
#endif

#ifndef ENTT_API
#    if defined ENTT_API_EXPORT
#        define ENTT_API ENTT_EXPORT
#    elif defined ENTT_API_IMPORT
#        define ENTT_API ENTT_IMPORT
#    else /* No API */
#        define ENTT_API
#    endif
#endif

#endif

// #include "fwd.hpp"

// #include "hashed_string.hpp"
#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP

#include <cstddef>
#include <cstdint>
// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename>
struct fnv1a_traits;

template<>
struct fnv1a_traits<std::uint32_t> {
    using type = std::uint32_t;
    static constexpr std::uint32_t offset = 2166136261;
    static constexpr std::uint32_t prime = 16777619;
};

template<>
struct fnv1a_traits<std::uint64_t> {
    using type = std::uint64_t;
    static constexpr std::uint64_t offset = 14695981039346656037ull;
    static constexpr std::uint64_t prime = 1099511628211ull;
};

template<typename Char>
struct basic_hashed_string {
    using value_type = Char;
    using size_type = std::size_t;
    using hash_type = id_type;

    const value_type *repr;
    size_type length;
    hash_type hash;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Zero overhead unique identifier.
 *
 * A hashed string is a compile-time tool that allows users to use
 * human-readable identifiers in the codebase while using their numeric
 * counterparts at runtime.<br/>
 * Because of that, a hashed string can also be used in constant expressions if
 * required.
 *
 * @warning
 * This class doesn't take ownership of user-supplied strings nor does it make a
 * copy of them.
 *
 * @tparam Char Character type.
 */
template<typename Char>
class basic_hashed_string: internal::basic_hashed_string<Char> {
    using base_type = internal::basic_hashed_string<Char>;
    using hs_traits = internal::fnv1a_traits<id_type>;

    struct const_wrapper {
        // non-explicit constructor on purpose
        constexpr const_wrapper(const Char *str) noexcept
            : repr{str} {}

        const Char *repr;
    };

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str) noexcept {
        base_type base{str, 0u, hs_traits::offset};

        for(; str[base.length]; ++base.length) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[base.length])) * hs_traits::prime;
        }

        return base;
    }

    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const Char *str, const std::size_t len) noexcept {
        base_type base{str, len, hs_traits::offset};

        for(size_type pos{}; pos < len; ++pos) {
            base.hash = (base.hash ^ static_cast<hs_traits::type>(str[pos])) * hs_traits::prime;
        }

        return base;
    }

public:
    /*! @brief Character type. */
    using value_type = typename base_type::value_type;
    /*! @brief Unsigned integer type. */
    using size_type = typename base_type::size_type;
    /*! @brief Unsigned integer type. */
    using hash_type = typename base_type::hash_type;

    /**
     * @brief Returns directly the numeric representation of a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const value_type *str, const size_type len) noexcept {
        return basic_hashed_string{str, len};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     * @return The numeric representation of the string.
     */
    template<std::size_t N>
    [[nodiscard]] static constexpr hash_type value(const value_type (&str)[N]) noexcept {
        return basic_hashed_string{str};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @param wrapper Helps achieving the purpose by relying on overloading.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const_wrapper wrapper) noexcept {
        return basic_hashed_string{wrapper};
    }

    /*! @brief Constructs an empty hashed string. */
    constexpr basic_hashed_string() noexcept
        : base_type{} {}

    /**
     * @brief Constructs a hashed string from a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     */
    constexpr basic_hashed_string(const value_type *str, const size_type len) noexcept
        : base_type{helper(str, len)} {}

    /**
     * @brief Constructs a hashed string from an array of const characters.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     */
    template<std::size_t N>
    constexpr basic_hashed_string(const value_type (&str)[N]) noexcept
        : base_type{helper(str)} {}

    /**
     * @brief Explicit constructor on purpose to avoid constructing a hashed
     * string directly from a `const value_type *`.
     *
     * @warning
     * The lifetime of the string is not extended nor is it copied.
     *
     * @param wrapper Helps achieving the purpose by relying on overloading.
     */
    explicit constexpr basic_hashed_string(const_wrapper wrapper) noexcept
        : base_type{helper(wrapper.repr)} {}

    /**
     * @brief Returns the size a hashed string.
     * @return The size of the hashed string.
     */
    [[nodiscard]] constexpr size_type size() const noexcept {
        return base_type::length;
    }

    /**
     * @brief Returns the human-readable representation of a hashed string.
     * @return The string used to initialize the hashed string.
     */
    [[nodiscard]] constexpr const value_type *data() const noexcept {
        return base_type::repr;
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr hash_type value() const noexcept {
        return base_type::hash;
    }

    /*! @copydoc data */
    [[nodiscard]] constexpr operator const value_type *() const noexcept {
        return data();
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr operator hash_type() const noexcept {
        return value();
    }
};

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @param str Human-readable identifier.
 * @param len Length of the string to hash.
 */
template<typename Char>
basic_hashed_string(const Char *str, const std::size_t len) -> basic_hashed_string<Char>;

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @tparam N Number of characters of the identifier.
 * @param str Human-readable identifier.
 */
template<typename Char, std::size_t N>
basic_hashed_string(const Char (&str)[N]) -> basic_hashed_string<Char>;

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings are identical, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator==(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() == rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the two hashed strings differ, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than the second, false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() < rhs.value();
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator<=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two hashed strings.
 * @tparam Char Character type.
 * @param lhs A valid hashed string.
 * @param rhs A valid hashed string.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
template<typename Char>
[[nodiscard]] constexpr bool operator>=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs < rhs);
}

/*! @brief Aliases for common character types. */
using hashed_string = basic_hashed_string<char>;

/*! @brief Aliases for common character types. */
using hashed_wstring = basic_hashed_string<wchar_t>;

inline namespace literals {

/**
 * @brief User defined literal for hashed strings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed string.
 */
[[nodiscard]] constexpr hashed_string operator"" _hs(const char *str, std::size_t) noexcept {
    return hashed_string{str};
}

/**
 * @brief User defined literal for hashed wstrings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed wstring.
 */
[[nodiscard]] constexpr hashed_wstring operator"" _hws(const wchar_t *str, std::size_t) noexcept {
    return hashed_wstring{str};
}

} // namespace literals

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct ENTT_API type_index final {
    [[nodiscard]] static id_type next() noexcept {
        static ENTT_MAYBE_ATOMIC(id_type) value{};
        return value++;
    }
};

template<typename Type>
[[nodiscard]] constexpr auto stripped_type_name() noexcept {
#if defined ENTT_PRETTY_FUNCTION
    std::string_view pretty_function{ENTT_PRETTY_FUNCTION};
    auto first = pretty_function.find_first_not_of(' ', pretty_function.find_first_of(ENTT_PRETTY_FUNCTION_PREFIX) + 1);
    auto value = pretty_function.substr(first, pretty_function.find_last_of(ENTT_PRETTY_FUNCTION_SUFFIX) - first);
    return value;
#else
    return std::string_view{""};
#endif
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr std::string_view type_name(int) noexcept {
    constexpr auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type>
[[nodiscard]] static std::string_view type_name(char) noexcept {
    static const auto value = stripped_type_name<Type>();
    return value;
}

template<typename Type, auto = stripped_type_name<Type>().find_first_of('.')>
[[nodiscard]] static constexpr id_type type_hash(int) noexcept {
    constexpr auto stripped = stripped_type_name<Type>();
    constexpr auto value = hashed_string::value(stripped.data(), stripped.size());
    return value;
}

template<typename Type>
[[nodiscard]] static id_type type_hash(char) noexcept {
    static const auto value = [](const auto stripped) {
        return hashed_string::value(stripped.data(), stripped.size());
    }(stripped_type_name<Type>());
    return value;
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Type sequential identifier.
 * @tparam Type Type for which to generate a sequential identifier.
 */
template<typename Type, typename = void>
struct ENTT_API type_index final {
    /**
     * @brief Returns the sequential identifier of a given type.
     * @return The sequential identifier of a given type.
     */
    [[nodiscard]] static id_type value() noexcept {
        static const id_type value = internal::type_index::next();
        return value;
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type hash.
 * @tparam Type Type for which to generate a hash value.
 */
template<typename Type, typename = void>
struct type_hash final {
    /**
     * @brief Returns the numeric representation of a given type.
     * @return The numeric representation of the given type.
     */
#if defined ENTT_PRETTY_FUNCTION
    [[nodiscard]] static constexpr id_type value() noexcept {
        return internal::type_hash<Type>(0);
#else
    [[nodiscard]] static constexpr id_type value() noexcept {
        return type_index<Type>::value();
#endif
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator id_type() const noexcept {
        return value();
    }
};

/**
 * @brief Type name.
 * @tparam Type Type for which to generate a name.
 */
template<typename Type, typename = void>
struct type_name final {
    /**
     * @brief Returns the name of a given type.
     * @return The name of the given type.
     */
    [[nodiscard]] static constexpr std::string_view value() noexcept {
        return internal::type_name<Type>(0);
    }

    /*! @copydoc value */
    [[nodiscard]] constexpr operator std::string_view() const noexcept {
        return value();
    }
};

/*! @brief Implementation specific information about a type. */
struct type_info final {
    /**
     * @brief Constructs a type info object for a given type.
     * @tparam Type Type for which to construct a type info object.
     */
    template<typename Type>
    constexpr type_info(std::in_place_type_t<Type>) noexcept
        : seq{type_index<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          identifier{type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value()},
          alias{type_name<std::remove_cv_t<std::remove_reference_t<Type>>>::value()} {}

    /**
     * @brief Type index.
     * @return Type index.
     */
    [[nodiscard]] constexpr id_type index() const noexcept {
        return seq;
    }

    /**
     * @brief Type hash.
     * @return Type hash.
     */
    [[nodiscard]] constexpr id_type hash() const noexcept {
        return identifier;
    }

    /**
     * @brief Type name.
     * @return Type name.
     */
    [[nodiscard]] constexpr std::string_view name() const noexcept {
        return alias;
    }

private:
    id_type seq;
    id_type identifier;
    std::string_view alias;
};

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects are identical, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator==(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.hash() == rhs.hash();
}

/**
 * @brief Compares the contents of two type info objects.
 * @param lhs A type info object.
 * @param rhs A type info object.
 * @return True if the two type info objects differ, false otherwise.
 */
[[nodiscard]] inline constexpr bool operator!=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than the second, false otherwise.
 */
[[nodiscard]] constexpr bool operator<(const type_info &lhs, const type_info &rhs) noexcept {
    return lhs.index() < rhs.index();
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is less than or equal to the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator<=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(rhs < lhs);
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than the second, false
 * otherwise.
 */
[[nodiscard]] constexpr bool operator>(const type_info &lhs, const type_info &rhs) noexcept {
    return rhs < lhs;
}

/**
 * @brief Compares two type info objects.
 * @param lhs A valid type info object.
 * @param rhs A valid type info object.
 * @return True if the first element is greater than or equal to the second,
 * false otherwise.
 */
[[nodiscard]] constexpr bool operator>=(const type_info &lhs, const type_info &rhs) noexcept {
    return !(lhs < rhs);
}

/**
 * @brief Returns the type info object associated to a given type.
 *
 * The returned element refers to an object with static storage duration.<br/>
 * The type doesn't need to be a complete type. If the type is a reference, the
 * result refers to the referenced type. In all cases, top-level cv-qualifiers
 * are ignored.
 *
 * @tparam Type Type for which to generate a type info object.
 * @return A reference to a properly initialized type info object.
 */
template<typename Type>
[[nodiscard]] const type_info &type_id() noexcept {
    if constexpr(std::is_same_v<Type, std::remove_cv_t<std::remove_reference_t<Type>>>) {
        static type_info instance{std::in_place_type<Type>};
        return instance;
    } else {
        return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
    }
}

/*! @copydoc type_id */
template<typename Type>
[[nodiscard]] const type_info &type_id(Type &&) noexcept {
    return type_id<std::remove_cv_t<std::remove_reference_t<Type>>>();
}

} // namespace entt

#endif

// #include "../core/utility.hpp"
#ifndef ENTT_CORE_UTILITY_HPP
#define ENTT_CORE_UTILITY_HPP

#include <type_traits>
#include <utility>

namespace entt {

/*! @brief Identity function object (waiting for C++20). */
struct identity {
    /*! @brief Indicates that this is a transparent function object. */
    using is_transparent = void;

    /**
     * @brief Returns its argument unchanged.
     * @tparam Type Type of the argument.
     * @param value The actual argument.
     * @return The submitted value as-is.
     */
    template<class Type>
    [[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
        return std::forward<Type>(value);
    }
};

/**
 * @brief Constant utility to disambiguate overloaded members of a class.
 * @tparam Type Type of the desired overload.
 * @tparam Class Type of class to which the member belongs.
 * @param member A valid pointer to a member.
 * @return Pointer to the member.
 */
template<typename Type, typename Class>
[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
    return member;
}

/**
 * @brief Constant utility to disambiguate overloaded functions.
 * @tparam Func Function type of the desired overload.
 * @param func A valid pointer to a function.
 * @return Pointer to the function.
 */
template<typename Func>
[[nodiscard]] constexpr auto overload(Func *func) noexcept {
    return func;
}

/**
 * @brief Helper type for visitors.
 * @tparam Func Types of function objects.
 */
template<class... Func>
struct overloaded: Func... {
    using Func::operator()...;
};

/**
 * @brief Deduction guide.
 * @tparam Func Types of function objects.
 */
template<class... Func>
overloaded(Func...) -> overloaded<Func...>;

/**
 * @brief Basic implementation of a y-combinator.
 * @tparam Func Type of a potentially recursive function.
 */
template<class Func>
struct y_combinator {
    /**
     * @brief Constructs a y-combinator from a given function.
     * @param recursive A potentially recursive function.
     */
    constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
        : func{std::move(recursive)} {}

    /**
     * @brief Invokes a y-combinator and therefore its underlying function.
     * @tparam Args Types of arguments to use to invoke the underlying function.
     * @param args Parameters to use to invoke the underlying function.
     * @return Return value of the underlying function, if any.
     */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

    /*! @copydoc operator()() */
    template<class... Args>
    constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
        return func(*this, std::forward<Args>(args)...);
    }

private:
    Func func;
};

} // namespace entt

#endif

// #include "fwd.hpp"

// #include "sigh.hpp"
#ifndef ENTT_SIGNAL_SIGH_HPP
#define ENTT_SIGNAL_SIGH_HPP

#include <algorithm>
#include <functional>
#include <type_traits>
#include <utility>
#include <vector>
// #include "delegate.hpp"
#ifndef ENTT_SIGNAL_DELEGATE_HPP
#define ENTT_SIGNAL_DELEGATE_HPP

#include <cstddef>
#include <functional>
#include <tuple>
#include <type_traits>
#include <utility>
// #include "../config/config.h"

// #include "../core/type_traits.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

template<typename Ret, typename... Args>
constexpr auto function_pointer(Ret (*)(Args...)) -> Ret (*)(Args...);

template<typename Ret, typename Type, typename... Args, typename Other>
constexpr auto function_pointer(Ret (*)(Type, Args...), Other &&) -> Ret (*)(Args...);

template<typename Class, typename Ret, typename... Args, typename... Other>
constexpr auto function_pointer(Ret (Class::*)(Args...), Other &&...) -> Ret (*)(Args...);

template<typename Class, typename Ret, typename... Args, typename... Other>
constexpr auto function_pointer(Ret (Class::*)(Args...) const, Other &&...) -> Ret (*)(Args...);

template<typename Class, typename Type, typename... Other>
constexpr auto function_pointer(Type Class::*, Other &&...) -> Type (*)();

template<typename... Type>
using function_pointer_t = decltype(function_pointer(std::declval<Type>()...));

template<typename... Class, typename Ret, typename... Args>
[[nodiscard]] constexpr auto index_sequence_for(Ret (*)(Args...)) {
    return std::index_sequence_for<Class..., Args...>{};
}

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic delegate implementation.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 */
template<typename>
class delegate;

/**
 * @brief Utility class to use to send around functions and members.
 *
 * Unmanaged delegate for function pointers and members. Users of this class are
 * in charge of disconnecting instances before deleting them.
 *
 * A delegate can be used as a general purpose invoker without memory overhead
 * for free functions possibly with payloads and bound or unbound members.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 */
template<typename Ret, typename... Args>
class delegate<Ret(Args...)> {
    template<auto Candidate, std::size_t... Index>
    [[nodiscard]] auto wrap(std::index_sequence<Index...>) noexcept {
        return [](const void *, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            return static_cast<Ret>(std::invoke(Candidate, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

    template<auto Candidate, typename Type, std::size_t... Index>
    [[nodiscard]] auto wrap(Type &, std::index_sequence<Index...>) noexcept {
        return [](const void *payload, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            return static_cast<Ret>(std::invoke(Candidate, *curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

    template<auto Candidate, typename Type, std::size_t... Index>
    [[nodiscard]] auto wrap(Type *, std::index_sequence<Index...>) noexcept {
        return [](const void *payload, Args... args) -> Ret {
            [[maybe_unused]] const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
            return static_cast<Ret>(std::invoke(Candidate, curr, std::forward<type_list_element_t<Index, type_list<Args...>>>(std::get<Index>(arguments))...));
        };
    }

public:
    /*! @brief Function type of the contained target. */
    using function_type = Ret(const void *, Args...);
    /*! @brief Function type of the delegate. */
    using type = Ret(Args...);
    /*! @brief Return type of the delegate. */
    using result_type = Ret;

    /*! @brief Default constructor. */
    delegate() noexcept
        : instance{nullptr},
          fn{nullptr} {}

    /**
     * @brief Constructs a delegate with a given object or payload, if any.
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance Optional valid object that fits the purpose.
     */
    template<auto Candidate, typename... Type>
    delegate(connect_arg_t<Candidate>, Type &&...value_or_instance) noexcept {
        connect<Candidate>(std::forward<Type>(value_or_instance)...);
    }

    /**
     * @brief Constructs a delegate and connects an user defined function with
     * optional payload.
     * @param function Function to connect to the delegate.
     * @param payload User defined arbitrary data.
     */
    delegate(function_type *function, const void *payload = nullptr) noexcept {
        connect(function, payload);
    }

    /**
     * @brief Connects a free function or an unbound member to a delegate.
     * @tparam Candidate Function or member to connect to the delegate.
     */
    template<auto Candidate>
    void connect() noexcept {
        instance = nullptr;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
            fn = [](const void *, Args... args) -> Ret {
                return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
            };
        } else if constexpr(std::is_member_pointer_v<decltype(Candidate)>) {
            fn = wrap<Candidate>(internal::index_sequence_for<type_list_element_t<0, type_list<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
        } else {
            fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
        }
    }

    /**
     * @brief Connects a free function with payload or a bound member to a
     * delegate.
     *
     * The delegate isn't responsible for the connected object or the payload.
     * Users must always guarantee that the lifetime of the instance overcomes
     * the one of the delegate.<br/>
     * When used to connect a free function with payload, its signature must be
     * such that the instance is the first argument before the ones used to
     * define the delegate itself.
     *
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid reference that fits the purpose.
     */
    template<auto Candidate, typename Type>
    void connect(Type &value_or_instance) noexcept {
        instance = &value_or_instance;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type &, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
                return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }

    /**
     * @brief Connects a free function with payload or a bound member to a
     * delegate.
     *
     * @sa connect(Type &)
     *
     * @tparam Candidate Function or member to connect to the delegate.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid pointer that fits the purpose.
     */
    template<auto Candidate, typename Type>
    void connect(Type *value_or_instance) noexcept {
        instance = value_or_instance;

        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type *, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<constness_as_t<void, Type> *>(payload));
                return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }

    /**
     * @brief Connects an user defined function with optional payload to a
     * delegate.
     *
     * The delegate isn't responsible for the connected object or the payload.
     * Users must always guarantee that the lifetime of an instance overcomes
     * the one of the delegate.<br/>
     * The payload is returned as the first argument to the target function in
     * all cases.
     *
     * @param function Function to connect to the delegate.
     * @param payload User defined arbitrary data.
     */
    void connect(function_type *function, const void *payload = nullptr) noexcept {
        ENTT_ASSERT(function != nullptr, "Uninitialized function pointer");
        instance = payload;
        fn = function;
    }

    /**
     * @brief Resets a delegate.
     *
     * After a reset, a delegate cannot be invoked anymore.
     */
    void reset() noexcept {
        instance = nullptr;
        fn = nullptr;
    }

    /**
     * @brief Returns the instance or the payload linked to a delegate, if any.
     * @return An opaque pointer to the underlying data.
     */
    [[nodiscard]] const void *data() const noexcept {
        return instance;
    }

    /**
     * @brief Triggers a delegate.
     *
     * The delegate invokes the underlying function and returns the result.
     *
     * @warning
     * Attempting to trigger an invalid delegate results in undefined
     * behavior.
     *
     * @param args Arguments to use to invoke the underlying function.
     * @return The value returned by the underlying function.
     */
    Ret operator()(Args... args) const {
        ENTT_ASSERT(static_cast<bool>(*this), "Uninitialized delegate");
        return fn(instance, std::forward<Args>(args)...);
    }

    /**
     * @brief Checks whether a delegate actually stores a listener.
     * @return False if the delegate is empty, true otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        // no need to also test instance
        return !(fn == nullptr);
    }

    /**
     * @brief Compares the contents of two delegates.
     * @param other Delegate with which to compare.
     * @return False if the two contents differ, true otherwise.
     */
    [[nodiscard]] bool operator==(const delegate<Ret(Args...)> &other) const noexcept {
        return fn == other.fn && instance == other.instance;
    }

private:
    const void *instance;
    function_type *fn;
};

/**
 * @brief Compares the contents of two delegates.
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @param lhs A valid delegate object.
 * @param rhs A valid delegate object.
 * @return True if the two contents differ, false otherwise.
 */
template<typename Ret, typename... Args>
[[nodiscard]] bool operator!=(const delegate<Ret(Args...)> &lhs, const delegate<Ret(Args...)> &rhs) noexcept {
    return !(lhs == rhs);
}

/**
 * @brief Deduction guide.
 * @tparam Candidate Function or member to connect to the delegate.
 */
template<auto Candidate>
delegate(connect_arg_t<Candidate>) -> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;

/**
 * @brief Deduction guide.
 * @tparam Candidate Function or member to connect to the delegate.
 * @tparam Type Type of class or type of payload.
 */
template<auto Candidate, typename Type>
delegate(connect_arg_t<Candidate>, Type &&) -> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;

/**
 * @brief Deduction guide.
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 */
template<typename Ret, typename... Args>
delegate(Ret (*)(const void *, Args...), const void * = nullptr) -> delegate<Ret(Args...)>;

} // namespace entt

#endif

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Sink class.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 *
 * @tparam Type A valid signal handler type.
 */
template<typename Type>
class sink;

/**
 * @brief Unmanaged signal handler.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 *
 * @tparam Type A valid function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Allocator>
class sigh;

/**
 * @brief Unmanaged signal handler.
 *
 * It works directly with references to classes and pointers to member functions
 * as well as pointers to free functions. Users of this class are in charge of
 * disconnecting instances before deleting them.
 *
 * This class serves mainly two purposes:
 *
 * * Creating signals to use later to notify a bunch of listeners.
 * * Collecting results from a set of functions like in a voting system.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
class sigh<Ret(Args...), Allocator> {
    /*! @brief A sink is allowed to modify a signal. */
    friend class sink<sigh<Ret(Args...), Allocator>>;

    using alloc_traits = std::allocator_traits<Allocator>;
    using container_type = std::vector<delegate<Ret(Args...)>, typename alloc_traits::template rebind_alloc<delegate<Ret(Args...)>>>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Sink type. */
    using sink_type = sink<sigh<Ret(Args...), Allocator>>;

    /*! @brief Default constructor. */
    sigh() noexcept(std::is_nothrow_default_constructible_v<allocator_type> &&std::is_nothrow_constructible_v<container_type, const allocator_type &>)
        : sigh{allocator_type{}} {}

    /**
     * @brief Constructs a signal handler with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit sigh(const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, const allocator_type &>)
        : calls{allocator} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    sigh(const sigh &other) noexcept(std::is_nothrow_copy_constructible_v<container_type>)
        : calls{other.calls} {}

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    sigh(const sigh &other, const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, const container_type &, const allocator_type &>)
        : calls{other.calls, allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    sigh(sigh &&other) noexcept(std::is_nothrow_move_constructible_v<container_type>)
        : calls{std::move(other.calls)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    sigh(sigh &&other, const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, container_type &&, const allocator_type &>)
        : calls{std::move(other.calls), allocator} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This signal handler.
     */
    sigh &operator=(const sigh &other) noexcept(std::is_nothrow_copy_assignable_v<container_type>) {
        calls = other.calls;
        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This signal handler.
     */
    sigh &operator=(sigh &&other) noexcept(std::is_nothrow_move_assignable_v<container_type>) {
        calls = std::move(other.calls);
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given signal handler.
     * @param other Signal handler to exchange the content with.
     */
    void swap(sigh &other) noexcept(std::is_nothrow_swappable_v<container_type>) {
        using std::swap;
        swap(calls, other.calls);
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return calls.get_allocator();
    }

    /**
     * @brief Number of listeners connected to the signal.
     * @return Number of listeners currently connected.
     */
    [[nodiscard]] size_type size() const noexcept {
        return calls.size();
    }

    /**
     * @brief Returns false if at least a listener is connected to the signal.
     * @return True if the signal has no listeners connected, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return calls.empty();
    }

    /**
     * @brief Triggers a signal.
     *
     * All the listeners are notified. Order isn't guaranteed.
     *
     * @param args Arguments to use to invoke listeners.
     */
    void publish(Args... args) const {
        for(auto &&call: std::as_const(calls)) {
            call(args...);
        }
    }

    /**
     * @brief Collects return values from the listeners.
     *
     * The collector must expose a call operator with the following properties:
     *
     * * The return type is either `void` or such that it's convertible to
     *   `bool`. In the second case, a true value will stop the iteration.
     * * The list of parameters is empty if `Ret` is `void`, otherwise it
     *   contains a single element such that `Ret` is convertible to it.
     *
     * @tparam Func Type of collector to use, if any.
     * @param func A valid function object.
     * @param args Arguments to use to invoke listeners.
     */
    template<typename Func>
    void collect(Func func, Args... args) const {
        for(auto &&call: calls) {
            if constexpr(std::is_void_v<Ret>) {
                if constexpr(std::is_invocable_r_v<bool, Func>) {
                    call(args...);
                    if(func()) {
                        break;
                    }
                } else {
                    call(args...);
                    func();
                }
            } else {
                if constexpr(std::is_invocable_r_v<bool, Func, Ret>) {
                    if(func(call(args...))) {
                        break;
                    }
                } else {
                    func(call(args...));
                }
            }
        }
    }

private:
    container_type calls;
};

/**
 * @brief Connection class.
 *
 * Opaque object the aim of which is to allow users to release an already
 * estabilished connection without having to keep a reference to the signal or
 * the sink that generated it.
 */
class connection {
    /*! @brief A sink is allowed to create connection objects. */
    template<typename>
    friend class sink;

    connection(delegate<void(void *)> fn, void *ref)
        : disconnect{fn}, signal{ref} {}

public:
    /*! @brief Default constructor. */
    connection()
        : disconnect{},
          signal{} {}

    /**
     * @brief Checks whether a connection is properly initialized.
     * @return True if the connection is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(disconnect);
    }

    /*! @brief Breaks the connection. */
    void release() {
        if(disconnect) {
            disconnect(signal);
            disconnect.reset();
        }
    }

private:
    delegate<void(void *)> disconnect;
    void *signal;
};

/**
 * @brief Scoped connection class.
 *
 * Opaque object the aim of which is to allow users to release an already
 * estabilished connection without having to keep a reference to the signal or
 * the sink that generated it.<br/>
 * A scoped connection automatically breaks the link between the two objects
 * when it goes out of scope.
 */
struct scoped_connection {
    /*! @brief Default constructor. */
    scoped_connection() = default;

    /**
     * @brief Constructs a scoped connection from a basic connection.
     * @param other A valid connection object.
     */
    scoped_connection(const connection &other)
        : conn{other} {}

    /*! @brief Default copy constructor, deleted on purpose. */
    scoped_connection(const scoped_connection &) = delete;

    /**
     * @brief Move constructor.
     * @param other The scoped connection to move from.
     */
    scoped_connection(scoped_connection &&other) noexcept
        : conn{std::exchange(other.conn, {})} {}

    /*! @brief Automatically breaks the link on destruction. */
    ~scoped_connection() {
        conn.release();
    }

    /**
     * @brief Default copy assignment operator, deleted on purpose.
     * @return This scoped connection.
     */
    scoped_connection &operator=(const scoped_connection &) = delete;

    /**
     * @brief Move assignment operator.
     * @param other The scoped connection to move from.
     * @return This scoped connection.
     */
    scoped_connection &operator=(scoped_connection &&other) noexcept {
        conn = std::exchange(other.conn, {});
        return *this;
    }

    /**
     * @brief Acquires a connection.
     * @param other The connection object to acquire.
     * @return This scoped connection.
     */
    scoped_connection &operator=(connection other) {
        conn = std::move(other);
        return *this;
    }

    /**
     * @brief Checks whether a scoped connection is properly initialized.
     * @return True if the connection is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(conn);
    }

    /*! @brief Breaks the connection. */
    void release() {
        conn.release();
    }

private:
    connection conn;
};

/**
 * @brief Sink class.
 *
 * A sink is used to connect listeners to signals and to disconnect them.<br/>
 * The function type for a listener is the one of the signal to which it
 * belongs.
 *
 * The clear separation between a signal and a sink permits to store the former
 * as private data member without exposing the publish functionality to the
 * users of the class.
 *
 * @warning
 * Lifetime of a sink must not overcome that of the signal to which it refers.
 * In any other case, attempting to use a sink results in undefined behavior.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
class sink<sigh<Ret(Args...), Allocator>> {
    using signal_type = sigh<Ret(Args...), Allocator>;
    using difference_type = typename signal_type::container_type::difference_type;

    template<auto Candidate, typename Type>
    static void release(Type value_or_instance, void *signal) {
        sink{*static_cast<signal_type *>(signal)}.disconnect<Candidate>(value_or_instance);
    }

    template<auto Candidate>
    static void release(void *signal) {
        sink{*static_cast<signal_type *>(signal)}.disconnect<Candidate>();
    }

    auto before(delegate<Ret(Args...)> call) {
        const auto &calls = signal->calls;
        const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));

        sink other{*this};
        other.offset = calls.cend() - it;
        return other;
    }

public:
    /**
     * @brief Constructs a sink that is allowed to modify a given signal.
     * @param ref A valid reference to a signal object.
     */
    sink(sigh<Ret(Args...), Allocator> &ref) noexcept
        : offset{},
          signal{&ref} {}

    /**
     * @brief Returns false if at least a listener is connected to the sink.
     * @return True if the sink has no listeners connected, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return signal->calls.empty();
    }

    /**
     * @brief Returns a sink that connects before a given free function or an
     * unbound member.
     * @tparam Function A valid free function pointer.
     * @return A properly initialized sink object.
     */
    template<auto Function>
    [[nodiscard]] sink before() {
        delegate<Ret(Args...)> call{};
        call.template connect<Function>();
        return before(std::move(call));
    }

    /**
     * @brief Returns a sink that connects before a free function with payload
     * or a bound member.
     * @tparam Candidate Member or free function to look for.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     * @return A properly initialized sink object.
     */
    template<auto Candidate, typename Type>
    [[nodiscard]] sink before(Type &&value_or_instance) {
        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance);
        return before(std::move(call));
    }

    /**
     * @brief Returns a sink that connects before a given instance or specific
     * payload.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     * @return A properly initialized sink object.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<std::remove_pointer_t<Type>>, void>, sink>>
    [[nodiscard]] sink before(Type &value_or_instance) {
        return before(&value_or_instance);
    }

    /**
     * @brief Returns a sink that connects before a given instance or specific
     * payload.
     * @param value_or_instance A valid pointer that fits the purpose.
     * @return A properly initialized sink object.
     */
    [[nodiscard]] sink before(const void *value_or_instance) {
        sink other{*this};

        if(value_or_instance) {
            const auto &calls = signal->calls;
            const auto it = std::find_if(calls.cbegin(), calls.cend(), [value_or_instance](const auto &delegate) {
                return delegate.data() == value_or_instance;
            });

            other.offset = calls.cend() - it;
        }

        return other;
    }

    /**
     * @brief Returns a sink that connects before anything else.
     * @return A properly initialized sink object.
     */
    [[nodiscard]] sink before() {
        sink other{*this};
        other.offset = signal->calls.size();
        return other;
    }

    /**
     * @brief Connects a free function (with or without payload), a bound or an
     * unbound member to a signal.
     *
     * The signal isn't responsible for the connected object or the payload, if
     * any. Users must guarantee that the lifetime of the instance overcomes the
     * one of the signal. On the other side, the signal handler performs
     * checks to avoid multiple connections for the same function.<br/>
     * When used to connect a free function with payload, its signature must be
     * such that the instance is the first argument before the ones used to
     * define the signal itself.
     *
     * @tparam Candidate Function or member to connect to the signal.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance A valid object that fits the purpose, if any.
     * @return A properly initialized connection object.
     */
    template<auto Candidate, typename... Type>
    connection connect(Type &&...value_or_instance) {
        disconnect<Candidate>(value_or_instance...);

        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance...);
        signal->calls.insert(signal->calls.end() - offset, std::move(call));

        delegate<void(void *)> conn{};
        conn.template connect<&release<Candidate, Type...>>(value_or_instance...);
        return {std::move(conn), signal};
    }

    /**
     * @brief Disconnects a free function (with or without payload), a bound or
     * an unbound member from a signal.
     * @tparam Candidate Function or member to disconnect from the signal.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance A valid object that fits the purpose, if any.
     */
    template<auto Candidate, typename... Type>
    void disconnect(Type &&...value_or_instance) {
        auto &calls = signal->calls;
        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance...);
        calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
    }

    /**
     * @brief Disconnects free functions with payload or bound members from a
     * signal.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<std::remove_pointer_t<Type>>, void>>>
    void disconnect(Type &value_or_instance) {
        disconnect(&value_or_instance);
    }

    /**
     * @brief Disconnects free functions with payload or bound members from a
     * signal.
     * @param value_or_instance A valid object that fits the purpose.
     */
    void disconnect(const void *value_or_instance) {
        if(value_or_instance) {
            auto &calls = signal->calls;
            auto predicate = [value_or_instance](const auto &delegate) { return delegate.data() == value_or_instance; };
            calls.erase(std::remove_if(calls.begin(), calls.end(), std::move(predicate)), calls.end());
        }
    }

    /*! @brief Disconnects all the listeners from a signal. */
    void disconnect() {
        signal->calls.clear();
    }

private:
    difference_type offset;
    signal_type *signal;
};

/**
 * @brief Deduction guide.
 *
 * It allows to deduce the signal handler type of a sink directly from the
 * signal it refers to.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
sink(sigh<Ret(Args...), Allocator> &) -> sink<sigh<Ret(Args...), Allocator>>;

} // namespace entt

#endif


namespace entt {

/**
 * @cond TURN_OFF_DOXYGEN
 * Internal details not to be documented.
 */

namespace internal {

struct basic_dispatcher_handler {
    virtual ~basic_dispatcher_handler() = default;
    virtual void publish() = 0;
    virtual void disconnect(void *) = 0;
    virtual void clear() noexcept = 0;
    virtual std::size_t size() const noexcept = 0;
};

template<typename Type, typename Allocator>
class dispatcher_handler final: public basic_dispatcher_handler {
    static_assert(std::is_same_v<Type, std::decay_t<Type>>, "Invalid type");

    using alloc_traits = std::allocator_traits<Allocator>;
    using signal_type = sigh<void(Type &), Allocator>;
    using container_type = std::vector<Type, typename alloc_traits::template rebind_alloc<Type>>;

public:
    using allocator_type = Allocator;

    dispatcher_handler(const allocator_type &allocator)
        : signal{allocator},
          events{allocator} {}

    void publish() override {
        const auto length = events.size();

        for(std::size_t pos{}; pos < length; ++pos) {
            signal.publish(events[pos]);
        }

        events.erase(events.cbegin(), events.cbegin() + length);
    }

    void disconnect(void *instance) override {
        bucket().disconnect(instance);
    }

    void clear() noexcept override {
        events.clear();
    }

    [[nodiscard]] auto bucket() noexcept {
        return typename signal_type::sink_type{signal};
    }

    void trigger(Type event) {
        signal.publish(event);
    }

    template<typename... Args>
    void enqueue(Args &&...args) {
        if constexpr(std::is_aggregate_v<Type>) {
            events.push_back(Type{std::forward<Args>(args)...});
        } else {
            events.emplace_back(std::forward<Args>(args)...);
        }
    }

    std::size_t size() const noexcept override {
        return events.size();
    }

private:
    signal_type signal;
    container_type events;
};

} // namespace internal

/**
 * Internal details not to be documented.
 * @endcond
 */

/**
 * @brief Basic dispatcher implementation.
 *
 * A dispatcher can be used either to trigger an immediate event or to enqueue
 * events to be published all together once per tick.<br/>
 * Listeners are provided in the form of member functions. For each event of
 * type `Type`, listeners are such that they can be invoked with an argument of
 * type `Type &`, no matter what the return type is.
 *
 * The dispatcher creates instances of the `sigh` class internally. Refer to the
 * documentation of the latter for more details.
 *
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Allocator>
class basic_dispatcher {
    template<typename Type>
    using handler_type = internal::dispatcher_handler<Type, Allocator>;

    using key_type = id_type;
    // std::shared_ptr because of its type erased allocator which is useful here
    using mapped_type = std::shared_ptr<internal::basic_dispatcher_handler>;

    using alloc_traits = std::allocator_traits<Allocator>;
    using container_allocator = typename alloc_traits::template rebind_alloc<std::pair<const key_type, mapped_type>>;
    using container_type = dense_map<key_type, mapped_type, identity, std::equal_to<key_type>, container_allocator>;

    template<typename Type>
    [[nodiscard]] handler_type<Type> &assure(const id_type id) {
        static_assert(std::is_same_v<Type, std::decay_t<Type>>, "Non-decayed types not allowed");
        auto &&ptr = pools.first()[id];

        if(!ptr) {
            const auto &allocator = get_allocator();
            ptr = std::allocate_shared<handler_type<Type>>(allocator, allocator);
        }

        return static_cast<handler_type<Type> &>(*ptr);
    }

    template<typename Type>
    [[nodiscard]] const handler_type<Type> *assure(const id_type id) const {
        static_assert(std::is_same_v<Type, std::decay_t<Type>>, "Non-decayed types not allowed");

        if(auto it = pools.first().find(id); it != pools.first().cend()) {
            return static_cast<const handler_type<Type> *>(it->second.get());
        }

        return nullptr;
    }

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;

    /*! @brief Default constructor. */
    basic_dispatcher()
        : basic_dispatcher{allocator_type{}} {}

    /**
     * @brief Constructs a dispatcher with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit basic_dispatcher(const allocator_type &allocator)
        : pools{allocator, allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    basic_dispatcher(basic_dispatcher &&other) noexcept
        : pools{std::move(other.pools)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    basic_dispatcher(basic_dispatcher &&other, const allocator_type &allocator) noexcept
        : pools{container_type{std::move(other.pools.first()), allocator}, allocator} {}

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This dispatcher.
     */
    basic_dispatcher &operator=(basic_dispatcher &&other) noexcept {
        pools = std::move(other.pools);
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given dispatcher.
     * @param other Dispatcher to exchange the content with.
     */
    void swap(basic_dispatcher &other) {
        using std::swap;
        swap(pools, other.pools);
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return pools.second();
    }

    /**
     * @brief Returns the number of pending events for a given type.
     * @tparam Type Type of event for which to return the count.
     * @param id Name used to map the event queue within the dispatcher.
     * @return The number of pending events for the given type.
     */
    template<typename Type>
    size_type size(const id_type id = type_hash<Type>::value()) const noexcept {
        const auto *cpool = assure<std::decay_t<Type>>(id);
        return cpool ? cpool->size() : 0u;
    }

    /**
     * @brief Returns the total number of pending events.
     * @return The total number of pending events.
     */
    size_type size() const noexcept {
        size_type count{};

        for(auto &&cpool: pools.first()) {
            count += cpool.second->size();
        }

        return count;
    }

    /**
     * @brief Returns a sink object for the given event and queue.
     *
     * A sink is an opaque object used to connect listeners to events.
     *
     * The function type for a listener is _compatible_ with:
     *
     * @code{.cpp}
     * void(Type &);
     * @endcode
     *
     * The order of invocation of the listeners isn't guaranteed.
     *
     * @sa sink
     *
     * @tparam Type Type of event of which to get the sink.
     * @param id Name used to map the event queue within the dispatcher.
     * @return A temporary sink object.
     */
    template<typename Type>
    [[nodiscard]] auto sink(const id_type id = type_hash<Type>::value()) {
        return assure<Type>(id).bucket();
    }

    /**
     * @brief Triggers an immediate event of a given type.
     * @tparam Type Type of event to trigger.
     * @param value An instance of the given type of event.
     */
    template<typename Type>
    void trigger(Type &&value = {}) {
        trigger(type_hash<std::decay_t<Type>>::value(), std::forward<Type>(value));
    }

    /**
     * @brief Triggers an immediate event on a queue of a given type.
     * @tparam Type Type of event to trigger.
     * @param value An instance of the given type of event.
     * @param id Name used to map the event queue within the dispatcher.
     */
    template<typename Type>
    void trigger(const id_type id, Type &&value = {}) {
        assure<std::decay_t<Type>>(id).trigger(std::forward<Type>(value));
    }

    /**
     * @brief Enqueues an event of the given type.
     * @tparam Type Type of event to enqueue.
     * @tparam Args Types of arguments to use to construct the event.
     * @param args Arguments to use to construct the event.
     */
    template<typename Type, typename... Args>
    void enqueue(Args &&...args) {
        enqueue_hint<Type>(type_hash<Type>::value(), std::forward<Args>(args)...);
    }

    /**
     * @brief Enqueues an event of the given type.
     * @tparam Type Type of event to enqueue.
     * @param value An instance of the given type of event.
     */
    template<typename Type>
    void enqueue(Type &&value) {
        enqueue_hint(type_hash<std::decay_t<Type>>::value(), std::forward<Type>(value));
    }

    /**
     * @brief Enqueues an event of the given type.
     * @tparam Type Type of event to enqueue.
     * @tparam Args Types of arguments to use to construct the event.
     * @param id Name used to map the event queue within the dispatcher.
     * @param args Arguments to use to construct the event.
     */
    template<typename Type, typename... Args>
    void enqueue_hint(const id_type id, Args &&...args) {
        assure<Type>(id).enqueue(std::forward<Args>(args)...);
    }

    /**
     * @brief Enqueues an event of the given type.
     * @tparam Type Type of event to enqueue.
     * @param id Name used to map the event queue within the dispatcher.
     * @param value An instance of the given type of event.
     */
    template<typename Type>
    void enqueue_hint(const id_type id, Type &&value) {
        assure<std::decay_t<Type>>(id).enqueue(std::forward<Type>(value));
    }

    /**
     * @brief Utility function to disconnect everything related to a given value
     * or instance from a dispatcher.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     */
    template<typename Type>
    void disconnect(Type &value_or_instance) {
        disconnect(&value_or_instance);
    }

    /**
     * @brief Utility function to disconnect everything related to a given value
     * or instance from a dispatcher.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     */
    template<typename Type>
    void disconnect(Type *value_or_instance) {
        for(auto &&cpool: pools.first()) {
            cpool.second->disconnect(value_or_instance);
        }
    }

    /**
     * @brief Discards all the events stored so far in a given queue.
     * @tparam Type Type of event to discard.
     * @param id Name used to map the event queue within the dispatcher.
     */
    template<typename Type>
    void clear(const id_type id = type_hash<Type>::value()) {
        assure<Type>(id).clear();
    }

    /*! @brief Discards all the events queued so far. */
    void clear() noexcept {
        for(auto &&cpool: pools.first()) {
            cpool.second->clear();
        }
    }

    /**
     * @brief Delivers all the pending events of a given queue.
     * @tparam Type Type of event to send.
     * @param id Name used to map the event queue within the dispatcher.
     */
    template<typename Type>
    void update(const id_type id = type_hash<Type>::value()) {
        assure<Type>(id).publish();
    }

    /*! @brief Delivers all the pending events. */
    void update() const {
        for(auto &&cpool: pools.first()) {
            cpool.second->publish();
        }
    }

private:
    compressed_pair<container_type, allocator_type> pools;
};

} // namespace entt

#endif

// #include "signal/emitter.hpp"
#ifndef ENTT_SIGNAL_EMITTER_HPP
#define ENTT_SIGNAL_EMITTER_HPP

#include <functional>
#include <type_traits>
#include <utility>
// #include "../container/dense_map.hpp"

// #include "../core/compressed_pair.hpp"

// #include "../core/fwd.hpp"

// #include "../core/type_info.hpp"

// #include "../core/utility.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief General purpose event emitter.
 *
 * To create an emitter type, derived classes must inherit from the base as:
 *
 * @code{.cpp}
 * struct my_emitter: emitter<my_emitter> {
 *     // ...
 * }
 * @endcode
 *
 * Handlers for the different events are created internally on the fly. It's not
 * required to specify in advance the full list of accepted events.<br/>
 * Moreover, whenever an event is published, an emitter also passes a reference
 * to itself to its listeners.
 *
 * @tparam Derived Emitter type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Derived, typename Allocator>
class emitter {
    using key_type = id_type;
    using mapped_type = std::function<void(void *)>;

    using alloc_traits = std::allocator_traits<Allocator>;
    using container_allocator = typename alloc_traits::template rebind_alloc<std::pair<const key_type, mapped_type>>;
    using container_type = dense_map<key_type, mapped_type, identity, std::equal_to<key_type>, container_allocator>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;

    /*! @brief Default constructor. */
    emitter()
        : emitter{allocator_type{}} {}

    /**
     * @brief Constructs an emitter with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit emitter(const allocator_type &allocator)
        : handlers{allocator, allocator} {}

    /*! @brief Default destructor. */
    virtual ~emitter() noexcept {
        static_assert(std::is_base_of_v<emitter<Derived, Allocator>, Derived>, "Invalid emitter type");
    }

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    emitter(emitter &&other) noexcept
        : handlers{std::move(other.handlers)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    emitter(emitter &&other, const allocator_type &allocator) noexcept
        : handlers{container_type{std::move(other.handlers.first()), allocator}, allocator} {}

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This dispatcher.
     */
    emitter &operator=(emitter &&other) noexcept {
        handlers = std::move(other.handlers);
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given emitter.
     * @param other Emitter to exchange the content with.
     */
    void swap(emitter &other) {
        using std::swap;
        swap(handlers, other.handlers);
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return handlers.second();
    }

    /**
     * @brief Publishes a given event.
     * @tparam Type Type of event to trigger.
     * @param value An instance of the given type of event.
     */
    template<typename Type>
    void publish(Type &&value) {
        if(const auto id = type_id<Type>().hash(); handlers.first().contains(id)) {
            handlers.first()[id](&value);
        }
    }

    /**
     * @brief Registers a listener with the event emitter.
     * @tparam Type Type of event to which to connect the listener.
     * @param func The listener to register.
     */
    template<typename Type>
    void on(std::function<void(Type &, Derived &)> func) {
        handlers.first().insert_or_assign(type_id<Type>().hash(), [func = std::move(func), this](void *value) {
            func(*static_cast<Type *>(value), static_cast<Derived &>(*this));
        });
    }

    /**
     * @brief Disconnects a listener from the event emitter.
     * @tparam Type Type of event of the listener.
     */
    template<typename Type>
    void erase() {
        handlers.first().erase(type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value());
    }

    /*! @brief Disconnects all the listeners. */
    void clear() noexcept {
        handlers.first().clear();
    }

    /**
     * @brief Checks if there are listeners registered for the specific event.
     * @tparam Type Type of event to test.
     * @return True if there are no listeners registered, false otherwise.
     */
    template<typename Type>
    [[nodiscard]] bool contains() const {
        return handlers.first().contains(type_hash<std::remove_cv_t<std::remove_reference_t<Type>>>::value());
    }

    /**
     * @brief Checks if there are listeners registered with the event emitter.
     * @return True if there are no listeners registered, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return handlers.first().empty();
    }

private:
    compressed_pair<container_type, allocator_type> handlers;
};

} // namespace entt

#endif

// #include "signal/sigh.hpp"
#ifndef ENTT_SIGNAL_SIGH_HPP
#define ENTT_SIGNAL_SIGH_HPP

#include <algorithm>
#include <functional>
#include <type_traits>
#include <utility>
#include <vector>
// #include "delegate.hpp"

// #include "fwd.hpp"


namespace entt {

/**
 * @brief Sink class.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 *
 * @tparam Type A valid signal handler type.
 */
template<typename Type>
class sink;

/**
 * @brief Unmanaged signal handler.
 *
 * Primary template isn't defined on purpose. All the specializations give a
 * compile-time error unless the template parameter is a function type.
 *
 * @tparam Type A valid function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Type, typename Allocator>
class sigh;

/**
 * @brief Unmanaged signal handler.
 *
 * It works directly with references to classes and pointers to member functions
 * as well as pointers to free functions. Users of this class are in charge of
 * disconnecting instances before deleting them.
 *
 * This class serves mainly two purposes:
 *
 * * Creating signals to use later to notify a bunch of listeners.
 * * Collecting results from a set of functions like in a voting system.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
class sigh<Ret(Args...), Allocator> {
    /*! @brief A sink is allowed to modify a signal. */
    friend class sink<sigh<Ret(Args...), Allocator>>;

    using alloc_traits = std::allocator_traits<Allocator>;
    using container_type = std::vector<delegate<Ret(Args...)>, typename alloc_traits::template rebind_alloc<delegate<Ret(Args...)>>>;

public:
    /*! @brief Allocator type. */
    using allocator_type = Allocator;
    /*! @brief Unsigned integer type. */
    using size_type = std::size_t;
    /*! @brief Sink type. */
    using sink_type = sink<sigh<Ret(Args...), Allocator>>;

    /*! @brief Default constructor. */
    sigh() noexcept(std::is_nothrow_default_constructible_v<allocator_type> &&std::is_nothrow_constructible_v<container_type, const allocator_type &>)
        : sigh{allocator_type{}} {}

    /**
     * @brief Constructs a signal handler with a given allocator.
     * @param allocator The allocator to use.
     */
    explicit sigh(const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, const allocator_type &>)
        : calls{allocator} {}

    /**
     * @brief Copy constructor.
     * @param other The instance to copy from.
     */
    sigh(const sigh &other) noexcept(std::is_nothrow_copy_constructible_v<container_type>)
        : calls{other.calls} {}

    /**
     * @brief Allocator-extended copy constructor.
     * @param other The instance to copy from.
     * @param allocator The allocator to use.
     */
    sigh(const sigh &other, const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, const container_type &, const allocator_type &>)
        : calls{other.calls, allocator} {}

    /**
     * @brief Move constructor.
     * @param other The instance to move from.
     */
    sigh(sigh &&other) noexcept(std::is_nothrow_move_constructible_v<container_type>)
        : calls{std::move(other.calls)} {}

    /**
     * @brief Allocator-extended move constructor.
     * @param other The instance to move from.
     * @param allocator The allocator to use.
     */
    sigh(sigh &&other, const allocator_type &allocator) noexcept(std::is_nothrow_constructible_v<container_type, container_type &&, const allocator_type &>)
        : calls{std::move(other.calls), allocator} {}

    /**
     * @brief Copy assignment operator.
     * @param other The instance to copy from.
     * @return This signal handler.
     */
    sigh &operator=(const sigh &other) noexcept(std::is_nothrow_copy_assignable_v<container_type>) {
        calls = other.calls;
        return *this;
    }

    /**
     * @brief Move assignment operator.
     * @param other The instance to move from.
     * @return This signal handler.
     */
    sigh &operator=(sigh &&other) noexcept(std::is_nothrow_move_assignable_v<container_type>) {
        calls = std::move(other.calls);
        return *this;
    }

    /**
     * @brief Exchanges the contents with those of a given signal handler.
     * @param other Signal handler to exchange the content with.
     */
    void swap(sigh &other) noexcept(std::is_nothrow_swappable_v<container_type>) {
        using std::swap;
        swap(calls, other.calls);
    }

    /**
     * @brief Returns the associated allocator.
     * @return The associated allocator.
     */
    [[nodiscard]] constexpr allocator_type get_allocator() const noexcept {
        return calls.get_allocator();
    }

    /**
     * @brief Number of listeners connected to the signal.
     * @return Number of listeners currently connected.
     */
    [[nodiscard]] size_type size() const noexcept {
        return calls.size();
    }

    /**
     * @brief Returns false if at least a listener is connected to the signal.
     * @return True if the signal has no listeners connected, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return calls.empty();
    }

    /**
     * @brief Triggers a signal.
     *
     * All the listeners are notified. Order isn't guaranteed.
     *
     * @param args Arguments to use to invoke listeners.
     */
    void publish(Args... args) const {
        for(auto &&call: std::as_const(calls)) {
            call(args...);
        }
    }

    /**
     * @brief Collects return values from the listeners.
     *
     * The collector must expose a call operator with the following properties:
     *
     * * The return type is either `void` or such that it's convertible to
     *   `bool`. In the second case, a true value will stop the iteration.
     * * The list of parameters is empty if `Ret` is `void`, otherwise it
     *   contains a single element such that `Ret` is convertible to it.
     *
     * @tparam Func Type of collector to use, if any.
     * @param func A valid function object.
     * @param args Arguments to use to invoke listeners.
     */
    template<typename Func>
    void collect(Func func, Args... args) const {
        for(auto &&call: calls) {
            if constexpr(std::is_void_v<Ret>) {
                if constexpr(std::is_invocable_r_v<bool, Func>) {
                    call(args...);
                    if(func()) {
                        break;
                    }
                } else {
                    call(args...);
                    func();
                }
            } else {
                if constexpr(std::is_invocable_r_v<bool, Func, Ret>) {
                    if(func(call(args...))) {
                        break;
                    }
                } else {
                    func(call(args...));
                }
            }
        }
    }

private:
    container_type calls;
};

/**
 * @brief Connection class.
 *
 * Opaque object the aim of which is to allow users to release an already
 * estabilished connection without having to keep a reference to the signal or
 * the sink that generated it.
 */
class connection {
    /*! @brief A sink is allowed to create connection objects. */
    template<typename>
    friend class sink;

    connection(delegate<void(void *)> fn, void *ref)
        : disconnect{fn}, signal{ref} {}

public:
    /*! @brief Default constructor. */
    connection()
        : disconnect{},
          signal{} {}

    /**
     * @brief Checks whether a connection is properly initialized.
     * @return True if the connection is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(disconnect);
    }

    /*! @brief Breaks the connection. */
    void release() {
        if(disconnect) {
            disconnect(signal);
            disconnect.reset();
        }
    }

private:
    delegate<void(void *)> disconnect;
    void *signal;
};

/**
 * @brief Scoped connection class.
 *
 * Opaque object the aim of which is to allow users to release an already
 * estabilished connection without having to keep a reference to the signal or
 * the sink that generated it.<br/>
 * A scoped connection automatically breaks the link between the two objects
 * when it goes out of scope.
 */
struct scoped_connection {
    /*! @brief Default constructor. */
    scoped_connection() = default;

    /**
     * @brief Constructs a scoped connection from a basic connection.
     * @param other A valid connection object.
     */
    scoped_connection(const connection &other)
        : conn{other} {}

    /*! @brief Default copy constructor, deleted on purpose. */
    scoped_connection(const scoped_connection &) = delete;

    /**
     * @brief Move constructor.
     * @param other The scoped connection to move from.
     */
    scoped_connection(scoped_connection &&other) noexcept
        : conn{std::exchange(other.conn, {})} {}

    /*! @brief Automatically breaks the link on destruction. */
    ~scoped_connection() {
        conn.release();
    }

    /**
     * @brief Default copy assignment operator, deleted on purpose.
     * @return This scoped connection.
     */
    scoped_connection &operator=(const scoped_connection &) = delete;

    /**
     * @brief Move assignment operator.
     * @param other The scoped connection to move from.
     * @return This scoped connection.
     */
    scoped_connection &operator=(scoped_connection &&other) noexcept {
        conn = std::exchange(other.conn, {});
        return *this;
    }

    /**
     * @brief Acquires a connection.
     * @param other The connection object to acquire.
     * @return This scoped connection.
     */
    scoped_connection &operator=(connection other) {
        conn = std::move(other);
        return *this;
    }

    /**
     * @brief Checks whether a scoped connection is properly initialized.
     * @return True if the connection is properly initialized, false otherwise.
     */
    [[nodiscard]] explicit operator bool() const noexcept {
        return static_cast<bool>(conn);
    }

    /*! @brief Breaks the connection. */
    void release() {
        conn.release();
    }

private:
    connection conn;
};

/**
 * @brief Sink class.
 *
 * A sink is used to connect listeners to signals and to disconnect them.<br/>
 * The function type for a listener is the one of the signal to which it
 * belongs.
 *
 * The clear separation between a signal and a sink permits to store the former
 * as private data member without exposing the publish functionality to the
 * users of the class.
 *
 * @warning
 * Lifetime of a sink must not overcome that of the signal to which it refers.
 * In any other case, attempting to use a sink results in undefined behavior.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
class sink<sigh<Ret(Args...), Allocator>> {
    using signal_type = sigh<Ret(Args...), Allocator>;
    using difference_type = typename signal_type::container_type::difference_type;

    template<auto Candidate, typename Type>
    static void release(Type value_or_instance, void *signal) {
        sink{*static_cast<signal_type *>(signal)}.disconnect<Candidate>(value_or_instance);
    }

    template<auto Candidate>
    static void release(void *signal) {
        sink{*static_cast<signal_type *>(signal)}.disconnect<Candidate>();
    }

    auto before(delegate<Ret(Args...)> call) {
        const auto &calls = signal->calls;
        const auto it = std::find(calls.cbegin(), calls.cend(), std::move(call));

        sink other{*this};
        other.offset = calls.cend() - it;
        return other;
    }

public:
    /**
     * @brief Constructs a sink that is allowed to modify a given signal.
     * @param ref A valid reference to a signal object.
     */
    sink(sigh<Ret(Args...), Allocator> &ref) noexcept
        : offset{},
          signal{&ref} {}

    /**
     * @brief Returns false if at least a listener is connected to the sink.
     * @return True if the sink has no listeners connected, false otherwise.
     */
    [[nodiscard]] bool empty() const noexcept {
        return signal->calls.empty();
    }

    /**
     * @brief Returns a sink that connects before a given free function or an
     * unbound member.
     * @tparam Function A valid free function pointer.
     * @return A properly initialized sink object.
     */
    template<auto Function>
    [[nodiscard]] sink before() {
        delegate<Ret(Args...)> call{};
        call.template connect<Function>();
        return before(std::move(call));
    }

    /**
     * @brief Returns a sink that connects before a free function with payload
     * or a bound member.
     * @tparam Candidate Member or free function to look for.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     * @return A properly initialized sink object.
     */
    template<auto Candidate, typename Type>
    [[nodiscard]] sink before(Type &&value_or_instance) {
        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance);
        return before(std::move(call));
    }

    /**
     * @brief Returns a sink that connects before a given instance or specific
     * payload.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     * @return A properly initialized sink object.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<std::remove_pointer_t<Type>>, void>, sink>>
    [[nodiscard]] sink before(Type &value_or_instance) {
        return before(&value_or_instance);
    }

    /**
     * @brief Returns a sink that connects before a given instance or specific
     * payload.
     * @param value_or_instance A valid pointer that fits the purpose.
     * @return A properly initialized sink object.
     */
    [[nodiscard]] sink before(const void *value_or_instance) {
        sink other{*this};

        if(value_or_instance) {
            const auto &calls = signal->calls;
            const auto it = std::find_if(calls.cbegin(), calls.cend(), [value_or_instance](const auto &delegate) {
                return delegate.data() == value_or_instance;
            });

            other.offset = calls.cend() - it;
        }

        return other;
    }

    /**
     * @brief Returns a sink that connects before anything else.
     * @return A properly initialized sink object.
     */
    [[nodiscard]] sink before() {
        sink other{*this};
        other.offset = signal->calls.size();
        return other;
    }

    /**
     * @brief Connects a free function (with or without payload), a bound or an
     * unbound member to a signal.
     *
     * The signal isn't responsible for the connected object or the payload, if
     * any. Users must guarantee that the lifetime of the instance overcomes the
     * one of the signal. On the other side, the signal handler performs
     * checks to avoid multiple connections for the same function.<br/>
     * When used to connect a free function with payload, its signature must be
     * such that the instance is the first argument before the ones used to
     * define the signal itself.
     *
     * @tparam Candidate Function or member to connect to the signal.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance A valid object that fits the purpose, if any.
     * @return A properly initialized connection object.
     */
    template<auto Candidate, typename... Type>
    connection connect(Type &&...value_or_instance) {
        disconnect<Candidate>(value_or_instance...);

        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance...);
        signal->calls.insert(signal->calls.end() - offset, std::move(call));

        delegate<void(void *)> conn{};
        conn.template connect<&release<Candidate, Type...>>(value_or_instance...);
        return {std::move(conn), signal};
    }

    /**
     * @brief Disconnects a free function (with or without payload), a bound or
     * an unbound member from a signal.
     * @tparam Candidate Function or member to disconnect from the signal.
     * @tparam Type Type of class or type of payload, if any.
     * @param value_or_instance A valid object that fits the purpose, if any.
     */
    template<auto Candidate, typename... Type>
    void disconnect(Type &&...value_or_instance) {
        auto &calls = signal->calls;
        delegate<Ret(Args...)> call{};
        call.template connect<Candidate>(value_or_instance...);
        calls.erase(std::remove(calls.begin(), calls.end(), std::move(call)), calls.end());
    }

    /**
     * @brief Disconnects free functions with payload or bound members from a
     * signal.
     * @tparam Type Type of class or type of payload.
     * @param value_or_instance A valid object that fits the purpose.
     */
    template<typename Type, typename = std::enable_if_t<!std::is_same_v<std::decay_t<std::remove_pointer_t<Type>>, void>>>
    void disconnect(Type &value_or_instance) {
        disconnect(&value_or_instance);
    }

    /**
     * @brief Disconnects free functions with payload or bound members from a
     * signal.
     * @param value_or_instance A valid object that fits the purpose.
     */
    void disconnect(const void *value_or_instance) {
        if(value_or_instance) {
            auto &calls = signal->calls;
            auto predicate = [value_or_instance](const auto &delegate) { return delegate.data() == value_or_instance; };
            calls.erase(std::remove_if(calls.begin(), calls.end(), std::move(predicate)), calls.end());
        }
    }

    /*! @brief Disconnects all the listeners from a signal. */
    void disconnect() {
        signal->calls.clear();
    }

private:
    difference_type offset;
    signal_type *signal;
};

/**
 * @brief Deduction guide.
 *
 * It allows to deduce the signal handler type of a sink directly from the
 * signal it refers to.
 *
 * @tparam Ret Return type of a function type.
 * @tparam Args Types of arguments of a function type.
 * @tparam Allocator Type of allocator used to manage memory and elements.
 */
template<typename Ret, typename... Args, typename Allocator>
sink(sigh<Ret(Args...), Allocator> &) -> sink<sigh<Ret(Args...), Allocator>>;

} // namespace entt

#endif

// IWYU pragma: end_exports