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<title>Unconstrained Sets</title>
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<div class="section boost_bimap_the_tutorial_unconstrained_sets">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="boost_bimap.the_tutorial.unconstrained_sets"></a><a class="link" href="unconstrained_sets.html" title="Unconstrained Sets">Unconstrained
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Sets</a>
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</h3></div></div></div>
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<p>
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Unconstrained sets allow the user to disable one of the views of a bimap.
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Doing so makes the bimap operations execute faster and reduces memory consumption.
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This completes the bidirectional mapping framework by including unidirectional
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mappings as a particular case.
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</p>
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<p>
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Unconstrained sets are useful for the following reasons:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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A bimap type has stronger guarantees than its standard equivalent, and
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includes some useful functions (replace, modify) that the standard does
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not have.
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</li>
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<li class="listitem">
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You can view the mapping as a collection of relations.
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</li>
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<li class="listitem">
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Using this kind of map makes the code very extensible. If, at any moment
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of the development, the need to perform searches from the right side
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of the mapping arises, the only necessary change is to the <code class="computeroutput"><span class="keyword">typedef</span></code>.
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</li>
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</ul></div>
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<p>
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Given this bimap instance,
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</p>
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<p>
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</p>
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<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">bimap</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">unconstrained_set_of</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="identifier">bm_type</span><span class="special">;</span>
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<span class="keyword">typedef</span> <span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_map</span> <span class="identifier">map_type</span><span class="special">;</span>
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<span class="identifier">bm_type</span> <span class="identifier">bm</span><span class="special">;</span>
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<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>
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</pre>
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<p>
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</p>
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<p>
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or this standard map one
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</p>
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<p>
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</p>
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<pre class="programlisting"><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>
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<span class="identifier">map_type</span> <span class="identifier">m</span><span class="special">;</span>
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</pre>
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<p>
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</p>
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<p>
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The following code snippet is valid
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</p>
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<p>
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</p>
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<pre class="programlisting"><span class="identifier">m</span><span class="special">[</span><span class="string">"one"</span><span class="special">]</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
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<span class="identifier">assert</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="string">"one"</span><span class="special">)</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>
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<span class="keyword">for</span><span class="special">(</span> <span class="identifier">map_type</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">m</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">m</span><span class="special">.</span><span class="identifier">end</span><span class="special">();</span> <span class="identifier">i</span> <span class="special">!=</span> <span class="identifier">iend</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span> <span class="special">)</span>
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<span class="special">{</span>
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<a class="co" name="boost_bimap.the_tutorial.unconstrained_sets.c0" href="unconstrained_sets.html#boost_bimap.the_tutorial.unconstrained_sets.c1"><img src="../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a><span class="special">++(</span><span class="identifier">i</span><span class="special">-></span><span class="identifier">second</span><span class="special">);</span>
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<span class="special">}</span>
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<span class="identifier">m</span><span class="special">.</span><span class="identifier">erase</span><span class="special">(</span><span class="string">"one"</span><span class="special">);</span>
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</pre>
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<p>
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</p>
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<div class="calloutlist"><table border="0" summary="Callout list"><tr>
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<td width="5%" valign="top" align="left"><p><a name="boost_bimap.the_tutorial.unconstrained_sets.c1"></a><a href="#boost_bimap.the_tutorial.unconstrained_sets.c0"><img src="../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td>
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<td valign="top" align="left"><p>
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The right collection of the bimap is mutable so its elements can be modified
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using iterators.
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</p></td>
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</tr></table></div>
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<p>
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But using a bimap has some benefits
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</p>
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<p>
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</p>
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<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">map_type</span><span class="special">::</span><span class="identifier">const_iterator</span> <span class="identifier">const_iterator</span><span class="special">;</span>
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<span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">const_iterator</span><span class="special">,</span><span class="identifier">const_iterator</span><span class="special">></span> <span class="identifier">const_range</span><span class="special">;</span>
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<a class="co" name="boost_bimap.the_tutorial.unconstrained_sets.c2" href="unconstrained_sets.html#boost_bimap.the_tutorial.unconstrained_sets.c3"><img src="../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a><span class="identifier">const_range</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">range</span><span class="special">(</span> <span class="string">"one"</span> <span class="special"><=</span> <span class="identifier">_key</span><span class="special">,</span> <span class="identifier">_key</span> <span class="special"><=</span> <span class="string">"two"</span> <span class="special">);</span>
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<span class="keyword">for</span><span class="special">(</span> <span class="identifier">const_iterator</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">r</span><span class="special">.</span><span class="identifier">first</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">!=</span> <span class="identifier">r</span><span class="special">.</span><span class="identifier">second</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span> <span class="special">)</span>
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<span class="special">{</span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">i</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">i</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>
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<span class="special">}</span>
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<span class="identifier">m</span><span class="special">.</span><span class="identifier">modify_key</span><span class="special">(</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">_key</span> <span class="special">=</span> <span class="string">"1"</span> <span class="special">);</span>
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</pre>
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<p>
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</p>
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<div class="calloutlist"><table border="0" summary="Callout list"><tr>
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<td width="5%" valign="top" align="left"><p><a name="boost_bimap.the_tutorial.unconstrained_sets.c3"></a><a href="#boost_bimap.the_tutorial.unconstrained_sets.c2"><img src="../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td>
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<td valign="top" align="left"><p>
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This range is a model of BidirectionalRange, read the docs of Boost.Range
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for more information.
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</p></td>
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</tr></table></div>
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<p>
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<a href="../../../../example/unconstrained_collection.cpp" target="_top">Go to source code</a>
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2006-2012 Matias Capeletto<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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</p>
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</div></td>
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</tr></table>
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