boost_mpl/doc/refmanual/at-c.html

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<div class="section" id="at-c">
<h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id354" name="at-c">at_c</a></h1>
<div class="section" id="intrinsic-at-synopsis">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
template&lt;
      typename Sequence
    , long n
    &gt;
struct <a href="./at-c.html" class="identifier">at_c</a>
{
    typedef <em>unspecified</em> type;
};
</pre>
</div>
<div class="section" id="intrinsic-at-description">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p>Returns a type identical to the <tt class="literal"><span class="pre">n</span></tt>th element from the beginning of 
the sequence. <tt class="literal"><span class="pre"><a href="./at-c.html" class="identifier">at_c</a>&lt;Sequence,n&gt;::type</span></tt> is a shorcut notation for 
<tt class="literal"><span class="pre"><a href="./at.html" class="identifier">at</a>&lt;</span> <span class="pre">Sequence,</span> <span class="pre"><a href="./long.html" class="identifier">long_</a>&lt;n&gt;</span> <span class="pre">&gt;::type</span></tt>.</p>
</div>
<div class="section" id="intrinsic-at-header">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/at.hpp" class="header">boost/mpl/at.hpp</a>&gt;
</pre>
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<div class="section" id="intrinsic-at-parameters">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<col width="36%" />
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<tr><th>Parameter</th>
<th>Requirement</th>
<th>Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
<td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
<td>A sequence to be examined.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">n</span></tt></td>
<td>A compile-time integral constant</td>
<td>An offset from the beginning of the sequence
specifying the element to be retrieved.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="intrinsic-at-expression-semantics">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<pre class="literal-block">
typedef <a href="./at-c.html" class="identifier">at_c</a>&lt;Sequence,n&gt;::type t; 
</pre>
<table class="field-list" frame="void" rules="none">
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<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type</td>
</tr>
<tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">0</span> <span class="pre">&lt;=</span> <span class="pre">n</span> <span class="pre">&lt;</span> <span class="pre"><a href="./size.html" class="identifier">size</a>&lt;Sequence&gt;::value</span></tt></td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
<pre class="last literal-block">
typedef <a href="./at.html" class="identifier">at</a>&lt; Sequence, <a href="./long.html" class="identifier">long_</a>&lt;n&gt; &gt;::type t;
</pre>
</td>
</tr>
</tbody>
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<div class="section" id="at-complexity">
<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
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<tr><th>Sequence archetype</th>
<th>Complexity</th>
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</thead>
<tbody valign="top">
<tr><td><a class="reference" href="./forward-sequence.html">Forward Sequence</a></td>
<td>Linear.</td>
</tr>
<tr><td><a class="reference" href="./random-access-sequence.html">Random Access Sequence</a></td>
<td>Amortized constant time.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="intrinsic-at-example">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
typedef <a href="./range-c.html" class="identifier">range_c</a>&lt;long,10,50&gt; range;
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( (<a href="./at-c.html" class="identifier">at_c</a>&lt; range,0 &gt;::value), ==, 10 );
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( (<a href="./at-c.html" class="identifier">at_c</a>&lt; range,10 &gt;::value), ==, 20 );
<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( (<a href="./at-c.html" class="identifier">at_c</a>&lt; range,40 &gt;::value), ==, 50 );
</pre>
</div>
<div class="section" id="intrinsic-at-see-also">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference" href="./random-access-sequence.html">Random Access Sequence</a>, <a class="refentry reference" href="./at.html"><tt class="refentry literal"><span class="pre">at</span></tt></a>, <a class="refentry reference" href="./front.html"><tt class="refentry literal"><span class="pre">front</span></tt></a>, <a class="refentry reference" href="./back.html"><tt class="refentry literal"><span class="pre">back</span></tt></a></p>
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