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<div><div><h5 class="title">
<a name="fusion.sequence.intrinsic.functions.at_key"></a><a href="at_key.html" title="at_key">at_key</a>
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<a name="fusion.sequence.intrinsic.functions.at_key.description"></a><h6>
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<p>
            Returns the element associated with a Key from the sequence.
          </p>
<a name="fusion.sequence.intrinsic.functions.at_key.synopsis"></a><h6>
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<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</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">&gt;</span>
<span class="keyword">typename</span> <a href="../metafunctions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></tt></a><span class="special">&lt;</span><span class="identifier">Sequence</span><span class="special">,</span> <span class="identifier">Key</span><span class="special">&gt;::</span><span class="identifier">type</span>
<span class="identifier">at_key</span><span class="special">(</span><span class="identifier">Sequence</span><span class="special">&amp;</span> <span class="identifier">seq</span><span class="special">);</span>

<span class="keyword">template</span> <span class="special">&lt;</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">&gt;</span>
<span class="keyword">typename</span> <a href="../metafunctions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></tt></a><span class="special">&lt;</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">,</span> <span class="identifier">Key</span><span class="special">&gt;::</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">&amp;</span> <span class="identifier">seq</span><span class="special">);</span>
</pre>
<a name="fusion.sequence.intrinsic.functions.at_key.parameters"></a><h6>
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<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>
                    <tt class="computeroutput"><span class="identifier">seq</span></tt>
                  </p></td>
<td><p>
                    Model of <a 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>
                    <tt class="computeroutput"><span class="identifier">Key</span></tt>
                  </p></td>
<td><p>
                    Any type
                  </p></td>
<td><p>
                    The queried key.
                  </p></td>
</tr>
</tbody>
</table></div>
<a name="fusion.sequence.intrinsic.functions.at_key.expression_semantics"></a><h6>
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            Semantics</a>
          </h6>
<pre class="programlisting"><span class="identifier">at_key</span><span class="special">&lt;</span><span class="identifier">Key</span><span class="special">&gt;(</span><span class="identifier">seq</span><span class="special">);</span>
</pre>
<p>
            <span class="bold"><b>Return type</b></span>: Returns a reference to
            the element associated with Key from the sequence <tt class="computeroutput"><span class="identifier">seq</span></tt>
            if <tt class="computeroutput"><span class="identifier">seq</span></tt> is mutable and
            <tt class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
            <span class="identifier">o</span></tt>, where <tt class="computeroutput"><span class="identifier">e</span></tt>
            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"><b>Precondition</b></span>: <tt class="computeroutput"><span class="identifier">has_key</span><span class="special">&lt;</span><span class="identifier">Key</span><span class="special">&gt;(</span><span class="identifier">seq</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></tt>
          </p>
<p>
            <span class="bold"><b>Semantics</b></span>: Returns the element associated
            with Key.
          </p>
<a name="fusion.sequence.intrinsic.functions.at_key.header"></a><h6>
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<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</span>
</pre>
<a name="fusion.sequence.intrinsic.functions.at_key.example"></a><h6>
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<pre class="programlisting"><a href="../../../container/set.html" title="set"><tt class="computeroutput"><span class="identifier">set</span></tt></a><span class="special">&lt;</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">&gt;</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">&lt;</span><span class="keyword">char</span><span class="special">&gt;(</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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