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<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="fusion.sequence.intrinsic.functions.at_key"></a><a class="link" href="at_key.html" title="at_key">at_key</a>
</h5></div></div></div>
<h6>
<a name="fusion.sequence.intrinsic.functions.at_key.h0"></a>
<span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.description"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.description">Description</a>
</h6>
<p>
Returns the element associated with a Key from the sequence.
</p>
<h6>
<a name="fusion.sequence.intrinsic.functions.at_key.h1"></a>
<span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.synopsis"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.synopsis">Synopsis</a>
</h6>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Key</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span>
<span class="keyword">typename</span> <a class="link" href="../metafunctions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">,</span> <span class="identifier">Key</span><span class="special">>::</span><span class="identifier">type</span>
<span class="identifier">at_key</span><span class="special">(</span><span class="identifier">Sequence</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span>
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Key</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">></span>
<span class="keyword">typename</span> <a class="link" href="../metafunctions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></a><span class="special"><</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">,</span> <span class="identifier">Key</span><span class="special">>::</span><span class="identifier">type</span>
<span class="identifier">at_key</span><span class="special">(</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">);</span>
</pre>
<h6>
<a name="fusion.sequence.intrinsic.functions.at_key.h2"></a>
<span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.parameters"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.parameters">Parameters</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Requirement
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">seq</span></code>
</p>
</td>
<td>
<p>
Model of <a class="link" href="../../concepts/associative_sequence.html" title="Associative Sequence">Associative
Sequence</a>
</p>
</td>
<td>
<p>
The sequence we wish to investigate.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">Key</span></code>
</p>
</td>
<td>
<p>
Any type
</p>
</td>
<td>
<p>
The queried key.
</p>
</td>
</tr>
</tbody>
</table></div>
<h6>
<a name="fusion.sequence.intrinsic.functions.at_key.h3"></a>
<span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.expression_semantics"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.expression_semantics">Expression
Semantics</a>
</h6>
<pre class="programlisting"><span class="identifier">at_key</span><span class="special"><</span><span class="identifier">Key</span><span class="special">>(</span><span class="identifier">seq</span><span class="special">);</span>
</pre>
<p>
<span class="bold"><strong>Return type</strong></span>: Returns a reference to
the element associated with Key from the sequence <code class="computeroutput"><span class="identifier">seq</span></code>
if <code class="computeroutput"><span class="identifier">seq</span></code> is mutable and
<code class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
<span class="identifier">o</span></code>, where <code class="computeroutput"><span class="identifier">e</span></code>
is the element associated with Key, is a valid expression. Else, returns
a type convertable to the element associated with Key.
</p>
<p>
<span class="bold"><strong>Precondition</strong></span>: <code class="computeroutput"><span class="identifier">has_key</span><span class="special"><</span><span class="identifier">Key</span><span class="special">>(</span><span class="identifier">seq</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>
</p>
<p>
<span class="bold"><strong>Semantics</strong></span>: Returns the element associated
with Key.
</p>
<h6>
<a name="fusion.sequence.intrinsic.functions.at_key.h4"></a>
<span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.header"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.header">Header</a>
</h6>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">sequence</span><span class="special">/</span><span class="identifier">intrinsic</span><span class="special">/</span><span class="identifier">at_key</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">at_key</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
</pre>
<h6>
<a name="fusion.sequence.intrinsic.functions.at_key.h5"></a>
<span class="phrase"><a name="fusion.sequence.intrinsic.functions.at_key.example"></a></span><a class="link" href="at_key.html#fusion.sequence.intrinsic.functions.at_key.example">Example</a>
</h6>
<pre class="programlisting"><a class="link" href="../../../container/set.html" title="set"><code class="computeroutput"><span class="identifier">set</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">></span> <span class="identifier">s</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="char">'x'</span><span class="special">,</span> <span class="keyword">true</span><span class="special">);</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">at_key</span><span class="special"><</span><span class="keyword">char</span><span class="special">>(</span><span class="identifier">s</span><span class="special">)</span> <span class="special">==</span> <span class="char">'x'</span><span class="special">);</span>
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman,
Dan Marsden, Tobias Schwinger<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>
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