initial import, >900commits predate this

external/json/include/nlohmann/detail/json_ref.hpp

@@ -0,0 +1,76 @@
+#pragma once
+
+#include <initializer_list>
+#include <utility>
+
+#include <nlohmann/detail/meta/type_traits.hpp>
+
+namespace nlohmann
+{
+namespace detail
+{
+template<typename BasicJsonType>
+class json_ref
+{
+  public:
+    using value_type = BasicJsonType;
+
+    json_ref(value_type&& value)
+        : owned_value(std::move(value))
+        , value_ref(&owned_value)
+        , is_rvalue(true)
+    {}
+
+    json_ref(const value_type& value)
+        : value_ref(const_cast<value_type*>(&value))
+        , is_rvalue(false)
+    {}
+
+    json_ref(std::initializer_list<json_ref> init)
+        : owned_value(init)
+        , value_ref(&owned_value)
+        , is_rvalue(true)
+    {}
+
+    template <
+        class... Args,
+        enable_if_t<std::is_constructible<value_type, Args...>::value, int> = 0 >
+    json_ref(Args && ... args)
+        : owned_value(std::forward<Args>(args)...)
+        , value_ref(&owned_value)
+        , is_rvalue(true)
+    {}
+
+    // class should be movable only
+    json_ref(json_ref&&) = default;
+    json_ref(const json_ref&) = delete;
+    json_ref& operator=(const json_ref&) = delete;
+    json_ref& operator=(json_ref&&) = delete;
+    ~json_ref() = default;
+
+    value_type moved_or_copied() const
+    {
+        if (is_rvalue)
+        {
+            return std::move(*value_ref);
+        }
+        return *value_ref;
+    }
+
+    value_type const& operator*() const
+    {
+        return *static_cast<value_type const*>(value_ref);
+    }
+
+    value_type const* operator->() const
+    {
+        return static_cast<value_type const*>(value_ref);
+    }
+
+  private:
+    mutable value_type owned_value = nullptr;
+    value_type* value_ref = nullptr;
+    const bool is_rvalue = true;
+};
+}  // namespace detail
+}  // namespace nlohmann