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<div id="projectname">EnTT<span id="projectnumber"> 3.15.0</span>
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<div class="headertitle"><div class="title">Crash Course: containers</div></div>
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<div class="textblock"><p><a class="anchor" id="crash-course-containers"></a></p>
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<h1><a class="anchor" id="table-of-contents-1"></a>
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Table of Contents</h1>
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<li><a class="el" href="md_docs_2md_2config.html#introduction">Introduction</a></li>
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<li><a class="el" href="#containers">Containers</a><ul>
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<li><a class="el" href="#dense-map">Dense map</a></li>
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<li><a class="el" href="#dense-set">Dense set</a></li>
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</ul>
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</li>
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<li><a class="el" href="#adaptors">Adaptors</a><ul>
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<li><a class="el" href="#table">Table</a></li>
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<h1><a class="anchor" id="introduction-1"></a>
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Introduction</h1>
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<p>The standard C++ library offers a wide range of containers and adaptors already. It is really difficult to do better (although it is very easy to do worse, as many examples available online demonstrate).<br />
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<code>EnTT</code> does not try in any way to replace what is offered by the standard. Quite 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 functionalities by making available some containers and adaptors initially developed for internal use.</p>
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<p>This section of the library is likely to grow larger over time. However, for the moment it is quite small and mainly aimed at satisfying some internal needs.<br />
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For all containers and adaptors made available, full test coverage and stability over time is guaranteed as usual.</p>
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<h1><a class="anchor" id="containers"></a>
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Containers</h1>
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<h2><a class="anchor" id="dense-map"></a>
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Dense map</h2>
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<p>The dense map made available in <code>EnTT</code> is a hash map that aims to return a packed array of elements, so as to reduce the number of jumps in memory during iterations.<br />
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The implementation is based on <em>sparse sets</em> and each bucket is identified by an implicit list within the packed array itself.</p>
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<p>The interface is very close to its counterpart in the standard library, that is, the <code>std::unordered_map</code> class.<br />
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However, both local and non-local iterators returned by a dense map belong to the input iterator category although they respectively model the concepts of a <em>forward iterator</em> type and a <em>random access iterator</em> type.<br />
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This is because they return a pair of references rather than a reference to a pair. In other words, dense maps return a so called <em>proxy iterator</em> the value type of which is:</p>
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<ul>
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<li><code>std::pair<const Key &, Type &></code> for non-const iterator types.</li>
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<li><code>std::pair<const Key &, const Type &></code> for const iterator types.</li>
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</ul>
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<p>This is quite different from what any standard library map returns and should be taken into account when looking for a drop-in replacement.</p>
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<h2><a class="anchor" id="dense-set"></a>
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Dense set</h2>
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<p>The dense set made available in <code>EnTT</code> is a hash set that aims to return a packed array of elements, so as to reduce the number of jumps in memory during iterations.<br />
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The implementation is based on <em>sparse sets</em> and each bucket is identified by an implicit list within the packed array itself.</p>
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<p>The interface is in all respects similar to its counterpart in the standard library, that is, the <code>std::unordered_set</code> class.<br />
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However, this type of set also supports reverse iteration and therefore offers all the functions necessary for the purpose (such as <code>rbegin</code> and <code>rend</code>).</p>
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<h1><a class="anchor" id="adaptors"></a>
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Adaptors</h1>
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<h2><a class="anchor" id="table"></a>
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Table</h2>
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<p>The <code>basic_table</code> class is a container adaptor which manages multiple sequential containers together, treating them as different columns of the same table.<br />
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The <code>table</code> alias allows users to provide only the types to handle, using <code>std::vector</code> as the default sequential container.</p>
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<p>Only a small set of functions is provided, although very close to what the API of the <code>std::vector</code> class offers.<br />
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The internal implementation is purposely supported by a tuple of containers rather than a container of tuples. The purpose is to allow efficient access to single columns and not just access to the entire data set of the table.</p>
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<p>When a row is accessed, all data is returned in the form of a tuple containing (possibly const) references to the elements of the row itself.<br />
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Similarly, when a table is iterated, tuples of references to table elements are returned for each row. </p>
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