forked from Green-Sky/tomato
68 lines
2.6 KiB
Markdown
68 lines
2.6 KiB
Markdown
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# Crash Course: containers
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@cond TURN_OFF_DOXYGEN
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# Table of Contents
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* [Introduction](#introduction)
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* [Containers](#containers)
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* [Dense map](#dense-map)
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* [Dense set](#dense-set)
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@endcond TURN_OFF_DOXYGEN
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# Introduction
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The standard C++ library offers a wide range of containers and it's really
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difficult to do better (although it's very easy to do worse, as many examples
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available online demonstrate).<br/>
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`EnTT` doesn't try in any way to replace what is offered by the standard. Quite
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the opposite, given the widespread use that is made of standard containers.<br/>
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However, the library also tries to fill a gap in features and functionality by
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making available some containers initially developed for internal use.
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This section of the library is likely to grow larger over time. However, for the
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moment it's quite small and mainly aimed at satisfying some internal needs.<br/>
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For all containers made available, full test coverage and stability over time is
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guaranteed as usual.
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# Containers
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## Dense map
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The dense map made available in `EnTT` is a hash map that aims to return a
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packed array of elements, so as to reduce the number of jumps in memory during
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iterations.<br/>
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The implementation is based on _sparse sets_ and each bucket is identified by an
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implicit list within the packed array itself.
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The interface is very close to its counterpart in the standard library, that is,
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`std::unordered_map`.<br/>
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However, both local and non-local iterators returned by a dense map belong to
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the input iterator category although they respectively model the concepts of a
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_forward iterator_ type and a _random access iterator_ type.<br/>
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This is because they return a pair of references rather than a reference to a
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pair. In other words, dense maps return a so called _proxy iterator_ the value
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type of which is:
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* `std::pair<const Key &, Type &>` for non-const iterator types.
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* `std::pair<const Key &, const Type &>` for const iterator types.
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This is quite different from what any standard library map returns and should be
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taken into account when looking for a drop-in replacement.
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## Dense set
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The dense set made available in `EnTT` is a hash set that aims to return a
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packed array of elements, so as to reduce the number of jumps in memory during
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iterations.<br/>
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The implementation is based on _sparse sets_ and each bucket is identified by an
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implicit list within the packed array itself.
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The interface is in all respects similar to its counterpart in the standard
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library, that is, `std::unordered_set`.<br/>
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Therefore, there is no need to go into the API description.
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