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168 lines
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<title>at_key</title>
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<div class="section" lang="en">
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<div class="titlepage"><div><div><h5 class="title">
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<a name="fusion.sequence.intrinsic.metafunctions.at_key"></a><a href="at_key.html" title="at_key">at_key</a></h5></div></div></div>
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<a name="fusion.sequence.intrinsic.metafunctions.at_key.description"></a><h6>
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<a name="id516357"></a>
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<a href="at_key.html#fusion.sequence.intrinsic.metafunctions.at_key.description">Description</a>
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</h6>
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<p>
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Returns the result type of <a href="../functions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">at_key</span></tt></a>
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<sup>[<a name="id516396" href="#ftn.id516396">8</a>]</sup>
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.
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</p>
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<a name="fusion.sequence.intrinsic.metafunctions.at_key.synopsis"></a><h6>
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<a name="id516515"></a>
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<a href="at_key.html#fusion.sequence.intrinsic.metafunctions.at_key.synopsis">Synopsis</a>
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</h6>
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<pre class="programlisting">
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<span class="keyword">template</span><span class="special"><</span>
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<span class="keyword">typename</span> <span class="identifier">Seq</span><span class="special">,</span>
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<span class="keyword">typename</span> <span class="identifier">Key</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">at_key</span>
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<span class="special">{</span>
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<span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span> <span class="identifier">type</span><span class="special">;</span>
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<span class="special">};</span>
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</pre>
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<div class="table">
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<a name="id516633"></a><p class="title"><b>Table 1.30. Parameters</b></p>
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<table class="table" summary="Parameters">
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<colgroup>
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<col>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Parameter
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</p>
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</th>
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<th>
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<p>
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Requirement
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</p>
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</th>
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<th>
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<p>
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Description
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><span class="identifier">Seq</span></tt>
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</p>
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</td>
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<td>
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<p>
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A model of <a href="../../concepts/forward_sequence.html" title="Forward
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Sequence">Forward
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Sequence</a>
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</p>
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</td>
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<td>
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<p>
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Argument sequence
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<tt class="computeroutput"><span class="identifier">Key</span></tt>
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</p>
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</td>
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<td>
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<p>
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Any type
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</p>
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</td>
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<td>
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<p>
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Key type
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</p>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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<a name="fusion.sequence.intrinsic.metafunctions.at_key.expression_semantics"></a><h6>
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<a name="id516772"></a>
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<a href="at_key.html#fusion.sequence.intrinsic.metafunctions.at_key.expression_semantics">Expression
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Semantics</a>
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</h6>
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<pre class="programlisting">
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<span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span><span class="special"><</span><span class="identifier">Seq</span><span class="special">,</span> <span class="identifier">Key</span><span class="special">>::</span><span class="identifier">type</span>
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</pre>
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<p>
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<span class="bold"><b>Return type</b></span>: Any type.
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</p>
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<p>
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<span class="bold"><b>Semantics</b></span>: Returns the result of using
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<a href="../functions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">at_key</span></tt></a> to access the element
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with key type <tt class="computeroutput"><span class="identifier">Key</span></tt> in
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<tt class="computeroutput"><span class="identifier">Seq</span></tt>.
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</p>
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<p>
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/sequence/intrinsic/at_key.hpp>
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</p>
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<a name="fusion.sequence.intrinsic.metafunctions.at_key.example"></a><h6>
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<a name="id516924"></a>
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<a href="at_key.html#fusion.sequence.intrinsic.metafunctions.at_key.example">Example</a>
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</h6>
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<pre class="programlisting">
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<span class="keyword">typedef</span> <a href="../../../container/map.html" title="map"><tt class="computeroutput"><span class="identifier">map</span></tt></a><span class="special"><</span><a href="../../../support/pair.html" title="pair"><tt class="computeroutput"><span class="identifier">pair</span></tt></a><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>,</span> <a href="../../../support/pair.html" title="pair"><tt class="computeroutput"><span class="identifier">pair</span></tt></a><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>,</span> <a href="../../../support/pair.html" title="pair"><tt class="computeroutput"><span class="identifier">pair</span></tt></a><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">char</span><span class="special">></span> <span class="special">></span> <span class="identifier">mymap</span><span class="special">;</span>
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<span class="identifier">BOOST_MPL_ASSERT</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_same</span><span class="special"><</span><a href="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"><</span><span class="identifier">mymap</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> <span class="keyword">char</span><span class="special">&>));</span>
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</pre>
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<div class="footnotes">
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<br><hr width="100" align="left">
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<div class="footnote"><p><sup>[<a name="ftn.id516396" href="#id516396">8</a>] </sup>
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<a href="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> reflects the actual
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return type of the function <a href="../functions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">at_key</span></tt></a>. <span class="underline">_sequence</span>_s
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typically return references to its elements via the <a href="../functions/at_key.html" title="at_key"><tt class="computeroutput"><span class="identifier">at_key</span></tt></a> function. If you
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want to get the actual element type, use <a href="value_at_key.html" title="value_at_key"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at_key</span></tt></a>
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</p></div>
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</div>
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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 © 2001-2007 Joel de Guzman, Dan Marsden, Tobias
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Schwinger<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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