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| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework"></a><a class="link" href="discovering_the_bimap_framework.html" title="Discovering the bimap framework">Discovering |
| the bimap framework</a> |
| </h3></div></div></div> |
| <div class="toc"><dl> |
| <dt><span class="section"><a href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.interpreting_bidirectional_maps">Interpreting |
| bidirectional maps</a></span></dt> |
| <dt><span class="section"><a href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.standard_mapping_framework">Standard |
| mapping framework</a></span></dt> |
| <dt><span class="section"><a href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.bimap_mapping_framework">Bimap |
| mapping framework</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework.interpreting_bidirectional_maps"></a><a class="link" href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.interpreting_bidirectional_maps" title="Interpreting bidirectional maps">Interpreting |
| bidirectional maps</a> |
| </h4></div></div></div> |
| <p> |
| One way to interpret bidirectional maps is as a function between two collections |
| of data, lets call them the left and the right collection. An element in |
| this bimap is a relation between an element from the left collection and |
| an element from the right collection. The types of both collections defines |
| the bimap behaviour. We can view the stored data from the left side, as |
| a mapping between keys from the left collection and data from the right |
| one, or from the right side, as a mapping between keys from the right collection |
| and data from the left collection. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework.standard_mapping_framework"></a><a class="link" href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.standard_mapping_framework" title="Standard mapping framework">Standard |
| mapping framework</a> |
| </h4></div></div></div> |
| <p> |
| Relationships between data in the STL are represented by maps. A standard |
| map is a directed relation of keys from a left collection and data from |
| a right unconstrained collection. The following diagram shows the relationship |
| represented and the user's viewpoint. |
| </p> |
| <p> |
| <span class="inlinemediaobject"><img src="../../images/bimap/standard.mapping.framework.png" alt="standard.mapping.framework"></span> |
| </p> |
| <p> |
| The left collection type depends on the selected map type. For example |
| if the the map type is <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">multimap</span></code> |
| the collection type of X is a <code class="computeroutput"><span class="identifier">multiset_of</span></code>. |
| The following table shows the equivalent types for the std associative |
| containers. |
| </p> |
| <div class="table"> |
| <a name="id765312"></a><p class="title"><b>Table 1.1. std associative containers</b></p> |
| <div class="table-contents"><table class="table" summary="std associative containers"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| container |
| </p> |
| </th> |
| <th> |
| <p> |
| left collection type |
| </p> |
| </th> |
| <th> |
| <p> |
| right collection type |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">map</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">set_of</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| no constraints |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">multimap</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">multiset_of</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| no constraints |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unordered_map</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unordered_set_of</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| no constraints |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unordered_multimap</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unordered_multiset_of</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| no constraints |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| </div> |
| <br class="table-break"> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework.bimap_mapping_framework"></a><a class="link" href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.bimap_mapping_framework" title="Bimap mapping framework">Bimap |
| mapping framework</a> |
| </h4></div></div></div> |
| <p> |
| Boost.Bimap design is based on the STL, and extends the framework in a |
| natural way. The following diagram represents the new situation. |
| </p> |
| <p> |
| <span class="inlinemediaobject"><img src="../../images/bimap/extended.mapping.framework.png" alt="extended.mapping.framework"></span> |
| </p> |
| <p> |
| Notice that now the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">maps</span></code> |
| are a particular case of a Boost.Bimap container, where you can view only |
| one side of the relationship and can control the constraints of only one |
| of the collections. Boost.Bimap allows the user to view the relationship |
| from three viewpoints. You can view it from one side, obtaining a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code> compatible container, or you can |
| work directly with the whole relation. |
| </p> |
| <p> |
| The next diagram shows the layout of the relation and pairs of a bimap. |
| It is the one from the <span class="emphasis"><em>one minute tutorial</em></span> |
| </p> |
| <p> |
| <span class="inlinemediaobject"><img src="../../images/bimap/relation.and.pair.png" alt="relation.and.pair"></span> |
| </p> |
| <p> |
| Bimap pairs are signature-compatible with standard pairs but are different |
| from them. As you will see in other sections they can be tagged with user |
| defined names and additional information can be attached to them. You can |
| convert from <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pairs</span></code> to bimap pairs directly but the |
| reverse conversion is not provided. This mean that you can insert elements |
| in a bimap using algorithms like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">copy</span></code> |
| from containers <code class="computeroutput"><span class="identifier">like</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code>, |
| or use <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span></code> to add new elements. However |
| it is best to use <code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">left</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span> <span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_value_type</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span><span class="identifier">s</span><span class="special">)</span> <span class="special">)</span></code> instead |
| of <code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span><span class="identifier">s</span><span class="special">)</span> <span class="special">)</span></code> to avoid |
| an extra call to the copy constructor of each type. |
| </p> |
| <p> |
| The following code snippet shows the relation between a bimap and standard |
| maps. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"> |
| <p> |
| You have to used references to views, and not directly views object. |
| Views cannot be constructed as separate objects from the container they |
| belong to, so the following: |
| </p> |
| <pre class="programlisting"><span class="comment">// Wrong: we forgot the & after bm_type::left_type |
| </span><span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_map</span> <span class="identifier">lm</span> <span class="special">=</span> <span class="identifier">bm</span><span class="special">.</span><span class="identifier">left</span><span class="special">;</span> |
| </pre> |
| <p> |
| does not compile, since it is trying to construct the view object <code class="computeroutput"><span class="identifier">lm</span></code>. This is a common source of errors |
| in user code. |
| </p> |
| </td></tr> |
| </table></div> |
| <p> |
| <a href="../../../../example/standard_map_comparison.cpp" target="_top">Go to source code</a> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">Map</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CompatibleKey</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CompatibleData</span> <span class="special">></span> |
| <span class="keyword">void</span> <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">Map</span> <span class="special">&</span> <span class="identifier">m</span><span class="special">,</span> |
| <span class="keyword">const</span> <span class="identifier">CompatibleKey</span> <span class="special">&</span> <span class="identifier">key</span><span class="special">,</span> |
| <span class="keyword">const</span> <span class="identifier">CompatibleData</span> <span class="special">&</span> <span class="identifier">data</span> <span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">Map</span><span class="special">::</span><span class="identifier">value_type</span> <span class="identifier">value_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">Map</span><span class="special">::</span><span class="identifier">const_iterator</span> <span class="identifier">const_iterator</span><span class="special">;</span> |
| |
| <span class="identifier">m</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span> <span class="identifier">value_type</span><span class="special">(</span><span class="identifier">key</span><span class="special">,</span><span class="identifier">data</span><span class="special">)</span> <span class="special">);</span> |
| <span class="identifier">const_iterator</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">key</span><span class="special">);</span> |
| <span class="keyword">if</span><span class="special">(</span> <span class="identifier">iter</span> <span class="special">!=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> <span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">assert</span><span class="special">(</span> <span class="identifier">iter</span><span class="special">-></span><span class="identifier">first</span> <span class="special">==</span> <span class="identifier">key</span> <span class="special">);</span> |
| <span class="identifier">assert</span><span class="special">(</span> <span class="identifier">iter</span><span class="special">-></span><span class="identifier">second</span> <span class="special">==</span> <span class="identifier">data</span> <span class="special">);</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">iter</span><span class="special">-></span><span class="identifier">first</span> <span class="special"><<</span> <span class="string">" --> "</span> <span class="special"><<</span> <span class="identifier">iter</span><span class="special">-></span><span class="identifier">second</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="identifier">m</span><span class="special">.</span><span class="identifier">erase</span><span class="special">(</span><span class="identifier">key</span><span class="special">);</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">bimap</span><span class="special"><</span> <span class="identifier">set_of</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>,</span> <span class="identifier">set_of</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="identifier">bimap_type</span><span class="special">;</span> |
| <span class="identifier">bimap_type</span> <span class="identifier">bm</span><span class="special">;</span> |
| |
| <span class="comment">// Standard map |
| </span> <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">int</span> <span class="special">></span> <span class="identifier">map_type</span><span class="special">;</span> |
| <span class="identifier">map_type</span> <span class="identifier">m</span><span class="special">;</span> |
| |
| <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">m</span><span class="special">,</span> <span class="string">"one"</span><span class="special">,</span> <span class="number">1</span> <span class="special">);</span> |
| <span class="special">}</span> |
| |
| <span class="comment">// Left map view |
| </span> <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">bimap_type</span><span class="special">::</span><span class="identifier">left_map</span> <span class="identifier">map_type</span><span class="special">;</span> |
| <span class="identifier">map_type</span> <span class="special">&</span> <span class="identifier">m</span> <span class="special">=</span> <span class="identifier">bm</span><span class="special">.</span><span class="identifier">left</span><span class="special">;</span> |
| |
| <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">m</span><span class="special">,</span> <span class="string">"one"</span><span class="special">,</span> <span class="number">1</span> <span class="special">);</span> |
| <span class="special">}</span> |
| |
| <span class="comment">// Reverse standard map |
| </span> <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">></span> <span class="identifier">reverse_map_type</span><span class="special">;</span> |
| <span class="identifier">reverse_map_type</span> <span class="identifier">rm</span><span class="special">;</span> |
| |
| <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">rm</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span> <span class="string">"one"</span> <span class="special">);</span> |
| <span class="special">}</span> |
| |
| <span class="comment">// Right map view |
| </span> <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">bimap_type</span><span class="special">::</span><span class="identifier">right_map</span> <span class="identifier">reverse_map_type</span><span class="special">;</span> |
| <span class="identifier">reverse_map_type</span> <span class="special">&</span> <span class="identifier">rm</span> <span class="special">=</span> <span class="identifier">bm</span><span class="special">.</span><span class="identifier">right</span><span class="special">;</span> |
| |
| <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">rm</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span> <span class="string">"one"</span> <span class="special">);</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2006 -2007 Matias Capeletto<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
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