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<title>Unconstrained Sets</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_bimap.the_tutorial.unconstrained_sets"></a><a class="link" href="unconstrained_sets.html" title="Unconstrained Sets">Unconstrained
Sets</a>
</h3></div></div></div>
<p>
Unconstrained sets allow the user to disable one of the views of a bimap.
Doing so makes the bimap operations execute faster and reduces memory consumption.
This completes the bidirectional mapping framework by including unidirectional
mappings as a particular case.
</p>
<p>
Unconstrained sets are useful for the following reasons:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
A bimap type has stronger guarantees than its standard equivalent, and
includes some useful functions (replace, modify) that the standard does
not have.
</li>
<li class="listitem">
You can view the mapping as a collection of relations.
</li>
<li class="listitem">
Using this kind of map makes the code very extensible. If, at any moment
of the development, the need to perform searches from the right side
of the mapping arises, the only necessary change is to the <code class="computeroutput"><span class="keyword">typedef</span></code>.
</li>
</ul></div>
<p>
Given this bimap instance,
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">bimap</span><span class="special">&lt;</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">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">bm_type</span><span class="special">;</span>
<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>
<span class="identifier">bm_type</span> <span class="identifier">bm</span><span class="special">;</span>
<span class="identifier">map_type</span> <span class="special">&amp;</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>
</pre>
<p>
</p>
<p>
or this standard map one
</p>
<p>
</p>
<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">&lt;</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">&gt;</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>
</pre>
<p>
</p>
<p>
The following code snippet is valid
</p>
<p>
</p>
<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>
<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>
<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>
<span class="special">{</span>
<a class="co" name="boost_bimap14co" href="unconstrained_sets.html#boost_bimap14"><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">-&gt;</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="string">"one"</span><span class="special">);</span>
</pre>
<p>
</p>
<p>
</p>
<div class="calloutlist"><table border="0" summary="Callout list"><tr>
<td width="5%" valign="top" align="left"><p><a name="boost_bimap14"></a><a href="#boost_bimap14co"><img src="../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td>
<td valign="top" align="left"><p> The right collection of the bimap is mutable so its elements can be modified
using iterators. </p></td>
</tr></table></div>
<p>
</p>
<p>
But using a bimap has some benefits
</p>
<p>
</p>
<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>
<span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">const_iterator</span><span class="special">,</span><span class="identifier">const_iterator</span><span class="special">&gt;</span> <span class="identifier">const_range</span><span class="special">;</span>
<a class="co" name="boost_bimap15co" href="unconstrained_sets.html#boost_bimap15"><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">&lt;=</span> <span class="identifier">_key</span><span class="special">,</span> <span class="identifier">_key</span> <span class="special">&lt;=</span> <span class="string">"two"</span> <span class="special">);</span>
<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>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">i</span><span class="special">-&gt;</span><span class="identifier">first</span> <span class="special">&lt;&lt;</span> <span class="string">"--&gt;"</span> <span class="special">&lt;&lt;</span> <span class="identifier">i</span><span class="special">-&gt;</span><span class="identifier">second</span> <span class="special">&lt;&lt;</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="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>
</pre>
<p>
</p>
<p>
</p>
<div class="calloutlist"><table border="0" summary="Callout list"><tr>
<td width="5%" valign="top" align="left"><p><a name="boost_bimap15"></a><a href="#boost_bimap15co"><img src="../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td>
<td valign="top" align="left"><p> This range is a model of BidirectionalRange, read the docs of Boost.Range
for more information. </p></td>
</tr></table></div>
<p>
</p>
<p>
<a href="../../../../example/unconstrained_collection.cpp" target="_top">Go to source code</a>
</p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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