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<title>Bimaps with user defined names</title>
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<div class="section boost_bimap_the_tutorial_bimaps_with_user_defined_names">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_bimap.the_tutorial.bimaps_with_user_defined_names"></a><a class="link" href="bimaps_with_user_defined_names.html" title="Bimaps with user defined names">Bimaps
with user defined names</a>
</h3></div></div></div>
<p>
In the following example, the library user inserted comments to guide future
programmers:
</p>
<p>
<a href="../../../../example/user_defined_names.cpp" target="_top">Go to source code</a>
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">bimap</span>
<span class="special"><</span>
<span class="identifier">multiset_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="keyword">int</span>
<span class="special">></span> <span class="identifier">People</span><span class="special">;</span>
<span class="identifier">People</span> <span class="identifier">people</span><span class="special">;</span>
<span class="comment">// ...</span>
<span class="keyword">int</span> <span class="identifier">user_id</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cin</span> <span class="special">>></span> <span class="identifier">user_id</span><span class="special">;</span>
<span class="comment">// people.right : map<id,name></span>
<span class="identifier">People</span><span class="special">::</span><span class="identifier">right_const_iterator</span> <span class="identifier">id_iter</span> <span class="special">=</span> <span class="identifier">people</span><span class="special">.</span><span class="identifier">right</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">user_id</span><span class="special">);</span>
<span class="keyword">if</span><span class="special">(</span> <span class="identifier">id_iter</span> <span class="special">!=</span> <span class="identifier">people</span><span class="special">.</span><span class="identifier">right</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> <span class="special">)</span>
<span class="special">{</span>
<span class="comment">// first : id</span>
<span class="comment">// second : name</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"name: "</span> <span class="special"><<</span> <span class="identifier">id_iter</span><span class="special">-></span><span class="identifier">second</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span>
<span class="special"><<</span> <span class="string">"id: "</span> <span class="special"><<</span> <span class="identifier">id_iter</span><span class="special">-></span><span class="identifier">first</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
<span class="keyword">else</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="string">"Unknown id, users are:"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="comment">// people.left : map<name,id></span>
<span class="keyword">for</span><span class="special">(</span> <span class="identifier">People</span><span class="special">::</span><span class="identifier">left_const_iterator</span>
<span class="identifier">name_iter</span> <span class="special">=</span> <span class="identifier">people</span><span class="special">.</span><span class="identifier">left</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">iend</span> <span class="special">=</span> <span class="identifier">people</span><span class="special">.</span><span class="identifier">left</span><span class="special">.</span><span class="identifier">end</span><span class="special">();</span>
<span class="identifier">name_iter</span> <span class="special">!=</span> <span class="identifier">iend</span><span class="special">;</span> <span class="special">++</span><span class="identifier">name_iter</span> <span class="special">)</span>
<span class="special">{</span>
<span class="comment">// first : name</span>
<span class="comment">// second : id</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"name: "</span> <span class="special"><<</span> <span class="identifier">name_iter</span><span class="special">-></span><span class="identifier">first</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span>
<span class="special"><<</span> <span class="string">"id: "</span> <span class="special"><<</span> <span class="identifier">name_iter</span><span class="special">-></span><span class="identifier">second</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
In Boost.Bimap there is a better way to document the code and in the meantime
helping you to write more maintainable and readable code. You can tag the
two collections of the bimap so they can be accessed by more descriptive
names.
</p>
<p>
<span class="inlinemediaobject"><img src="../../images/bimap/tagged.png" alt="tagged"></span>
</p>
<p>
A tagged type is a type that has been labelled using a tag. A tag is any
valid C++ type. In a bimap, the types are always tagged. If you do not specify
your own tag, the container uses <code class="computeroutput"><span class="identifier">member_at</span><span class="special">::</span><span class="identifier">left</span></code>
and <code class="computeroutput"><span class="identifier">member_at</span><span class="special">::</span><span class="identifier">right</span></code> to tag the left and right sides respectively.
In order to specify a custom tag, the type of each side has to be tagged.
Tagging a type is very simple:
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">tagged</span><span class="special"><</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">a_tag</span> <span class="special">></span> <span class="identifier">tagged_int</span><span class="special">;</span>
</pre>
<p>
Now we can rewrite the example:
</p>
<p>
<a href="../../../../example/user_defined_names.cpp" target="_top">Go to source code</a>
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">id</span> <span class="special">{};</span> <span class="comment">// Tag for the identification number</span>
<span class="keyword">struct</span> <span class="identifier">name</span> <span class="special">{};</span> <span class="comment">// Tag for the name of the person</span>
<span class="keyword">typedef</span> <span class="identifier">bimap</span>
<span class="special"><</span>
<span class="identifier">tagged</span><span class="special"><</span> <span class="keyword">int</span> <span class="special">,</span> <span class="identifier">id</span> <span class="special">></span> <span class="special">,</span>
<span class="identifier">multiset_of</span><span class="special"><</span> <span class="identifier">tagged</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">name</span> <span class="special">></span> <span class="special">></span>
<span class="special">></span> <span class="identifier">People</span><span class="special">;</span>
<span class="identifier">People</span> <span class="identifier">people</span><span class="special">;</span>
<span class="comment">// ...</span>
<span class="keyword">int</span> <span class="identifier">user_id</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cin</span> <span class="special">>></span> <span class="identifier">user_id</span><span class="special">;</span>
<span class="identifier">People</span><span class="special">::</span><span class="identifier">map_by</span><span class="special"><</span><span class="identifier">id</span><span class="special">>::</span><span class="identifier">const_iterator</span> <span class="identifier">id_iter</span> <span class="special">=</span> <span class="identifier">people</span><span class="special">.</span><span class="identifier">by</span><span class="special"><</span><span class="identifier">id</span><span class="special">>().</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">user_id</span><span class="special">);</span>
<span class="keyword">if</span><span class="special">(</span> <span class="identifier">id_iter</span> <span class="special">!=</span> <span class="identifier">people</span><span class="special">.</span><span class="identifier">by</span><span class="special"><</span><span class="identifier">id</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">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"name: "</span> <span class="special"><<</span> <span class="identifier">id_iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">name</span><span class="special">>()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span>
<span class="special"><<</span> <span class="string">"id: "</span> <span class="special"><<</span> <span class="identifier">id_iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">id</span><span class="special">>()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
<span class="keyword">else</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="string">"Unknown id, users are:"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="keyword">for</span><span class="special">(</span> <span class="identifier">People</span><span class="special">::</span><span class="identifier">map_by</span><span class="special"><</span><span class="identifier">name</span><span class="special">>::</span><span class="identifier">const_iterator</span>
<span class="identifier">name_iter</span> <span class="special">=</span> <span class="identifier">people</span><span class="special">.</span><span class="identifier">by</span><span class="special"><</span><span class="identifier">name</span><span class="special">>().</span><span class="identifier">begin</span><span class="special">(),</span>
<span class="identifier">iend</span> <span class="special">=</span> <span class="identifier">people</span><span class="special">.</span><span class="identifier">by</span><span class="special"><</span><span class="identifier">name</span><span class="special">>().</span><span class="identifier">end</span><span class="special">();</span>
<span class="identifier">name_iter</span> <span class="special">!=</span> <span class="identifier">iend</span><span class="special">;</span> <span class="special">++</span><span class="identifier">name_iter</span> <span class="special">)</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="string">"name: "</span> <span class="special"><<</span> <span class="identifier">name_iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">name</span><span class="special">>()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span>
<span class="special"><<</span> <span class="string">"id: "</span> <span class="special"><<</span> <span class="identifier">name_iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">id</span><span class="special">>()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
Here is a list of common structures in both tagged and untagged versions.
Remember that when the bimap has user defined tags you can still use the
untagged version structures.
</p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">Left</span> <span class="special">{};</span>
<span class="keyword">struct</span> <span class="identifier">Right</span> <span class="special">{};</span>
<span class="keyword">typedef</span> <span class="identifier">bimap</span><span class="special"><</span>
<span class="identifier">multiset_of</span><span class="special"><</span> <span class="identifier">tagged</span><span class="special"><</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">Left</span> <span class="special">></span> <span class="special">>,</span>
<span class="identifier">unordered_set_of</span><span class="special"><</span> <span class="identifier">tagged</span><span class="special"><</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">Right</span> <span class="special">></span> <span class="special">></span>
<span class="special">></span> <span class="identifier">bm_type</span><span class="special">;</span>
<span class="identifier">bm_type</span> <span class="identifier">bm</span><span class="special">;</span>
<span class="comment">//...</span>
<span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">bm</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span>
<span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_iterator</span> <span class="identifier">left_iter</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">begin</span><span class="special">();</span>
<span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">right_iterator</span> <span class="identifier">right_iter</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">begin</span><span class="special">();</span>
</pre>
<div class="table">
<a name="boost_bimap.the_tutorial.bimaps_with_user_defined_names.t0"></a><p class="title"><b>Table 1.3. Equivalence of expresions using user defined names</b></p>
<div class="table-contents"><table class="table" summary="Equivalence of expresions using user defined names">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Untagged version
</p>
</th>
<th>
<p>
Tagged version
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">left</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">by</span><span class="special"><</span><span class="identifier">Left</span><span class="special">>()</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">right</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">by</span><span class="special"><</span><span class="identifier">Right</span><span class="special">>()</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_map</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">::</span><span class="identifier">map_by</span><span class="special"><</span><span class="identifier">Left</span><span class="special">>::</span><span class="identifier">type</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">right_value_type</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">::</span><span class="identifier">map_by</span><span class="special"><</span><span class="identifier">Right</span><span class="special">>::</span><span class="identifier">value_type</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_iterator</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">::</span><span class="identifier">map_by</span><span class="special"><</span><span class="identifier">Left</span><span class="special">>::</span><span class="identifier">iterator</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">right_const_iterator</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">::</span><span class="identifier">map_by</span><span class="special"><</span><span class="identifier">Right</span><span class="special">>::</span><span class="identifier">const_iterator</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">iter</span><span class="special">-></span><span class="identifier">left</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">Left</span><span class="special">>()</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">iter</span><span class="special">-></span><span class="identifier">right</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">Right</span><span class="special">>()</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">left_iter</span><span class="special">-></span><span class="identifier">first</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">left_iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">Left</span><span class="special">>()</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">left_iter</span><span class="special">-></span><span class="identifier">second</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">left_iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">Right</span><span class="special">>()</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">right_iter</span><span class="special">-></span><span class="identifier">first</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">right_iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">Right</span><span class="special">>()</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">right_iter</span><span class="special">-></span><span class="identifier">second</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">right_iter</span><span class="special">-></span><span class="identifier">get</span><span class="special"><</span><span class="identifier">Left</span><span class="special">>()</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">project_left</span><span class="special">(</span><span class="identifier">iter</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">project</span><span class="special"><</span><span class="identifier">Left</span><span class="special">>(</span><span class="identifier">iter</span><span class="special">)</span></code>
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">project_right</span><span class="special">(</span><span class="identifier">iter</span><span class="special">)</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">project</span><span class="special"><</span><span class="identifier">Right</span><span class="special">>(</span><span class="identifier">iter</span><span class="special">)</span></code>
</p>
</td>
</tr>
</tbody>
</table></div>
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<td align="right"><div class="copyright-footer">Copyright © 2006-2012 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>)
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