forked from boostorg/fusion
166 lines
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166 lines
11 KiB
HTML
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<link rel="home" href="../../../../index.html" title="Chapter 1. Fusion 2.0">
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<div class="section">
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<div class="titlepage"><div><div><h5 class="title">
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<a name="fusion.sequence.intrinsic.metafunctions.at"></a><a class="link" href="at.html" title="at">at</a>
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</h5></div></div></div>
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<a name="fusion.sequence.intrinsic.metafunctions.at.description"></a><h6>
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<a name="id891981"></a>
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<a class="link" href="at.html#fusion.sequence.intrinsic.metafunctions.at.description">Description</a>
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</h6>
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<p>
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Returns the result type of <a class="link" href="../functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a><sup>[<a name="id892002" href="#ftn.id892002" class="footnote">6</a>]</sup>.
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</p>
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<a name="fusion.sequence.intrinsic.metafunctions.at.synopsis"></a><h6>
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<a name="id892072"></a>
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<a class="link" href="at.html#fusion.sequence.intrinsic.metafunctions.at.synopsis">Synopsis</a>
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</h6>
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<pre class="programlisting"><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">N</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">at</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="id892156"></a><p class="title"><b>Table 1.29. Parameters</b></p>
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<div class="table-contents"><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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<code class="computeroutput"><span class="identifier">Seq</span></code>
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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 class="link" href="../../concepts/forward_sequence.html" title="Forward 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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<code class="computeroutput"><span class="identifier">N</span></code>
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</p>
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</td>
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<td>
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<p>
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An <a href="http://www.boost.org/libs/mpl/doc/refmanual/integral-constant.html" target="_top">MPL
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Integral Constant</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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Index of element
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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></div>
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</div>
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<br class="table-break"><a name="fusion.sequence.intrinsic.metafunctions.at.expression_semantics"></a><h6>
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<a name="id892285"></a>
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<a class="link" href="at.html#fusion.sequence.intrinsic.metafunctions.at.expression_semantics">Expression
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Semantics</a>
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</h6>
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<pre class="programlisting"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at</span><span class="special"><</span><span class="identifier">Seq</span><span class="special">,</span> <span class="identifier">N</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"><strong>Return type</strong></span>: Any type.
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</p>
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<p>
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<span class="bold"><strong>Semantics</strong></span>: Returns the result type of
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using <a class="link" href="../functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a> to access the <code class="computeroutput"><span class="identifier">N</span></code>th element of <code class="computeroutput"><span class="identifier">Seq</span></code>.
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</p>
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<a name="fusion.sequence.intrinsic.metafunctions.at.header"></a><h6>
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<a name="id892380"></a>
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<a class="link" href="at.html#fusion.sequence.intrinsic.metafunctions.at.header">Header</a>
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</h6>
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<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</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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<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</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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</pre>
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<a name="fusion.sequence.intrinsic.metafunctions.at.example"></a><h6>
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<a name="id892495"></a>
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<a class="link" href="at.html#fusion.sequence.intrinsic.metafunctions.at.example">Example</a>
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</h6>
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<pre class="programlisting"><span class="keyword">typedef</span> <a class="link" href="../../../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">float</span><span class="special">,</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">vec</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 class="link" href="at.html" title="at"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at</span></code></a><span class="special"><</span><span class="identifier">vec</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="number">1</span><span class="special">></span> <span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> <span class="keyword">float</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.id892002" href="#id892002" class="para">6</a>] </sup>
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<a class="link" href="at.html" title="at"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at</span></code></a> reflects the actual return
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type of the function <a class="link" href="../functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a>. <a class="link" href="../../../sequence.html" title="Sequence">Sequence</a>(s)
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typically return references to its elements via the <a class="link" href="../functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a> function. If you want to
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get the actual element type, use <a class="link" href="value_at.html" title="value_at"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at</span></code></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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