boost_fusion/doc/html/fusion/sequences/intrinsics/metafunctions/value_at.html

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<div class="titlepage"><div><div><h5 class="title">
<a name="fusion.sequences.intrinsics.metafunctions.value_at"></a><a href="value_at.html" title="value_at">value_at</a></h5></div></div></div>
<a name="fusion.sequences.intrinsics.metafunctions.value_at.description"></a><h6>
<a name="id517377"></a>
            <a href="value_at.html#fusion.sequences.intrinsics.metafunctions.value_at.description">Description</a>
          </h6>
<p>
            Returns the actual type at a given index from the <a href="../../../sequences.html" title="Sequences">Sequence</a>.
          </p>
<a name="fusion.sequences.intrinsics.metafunctions.value_at.synopsis"></a><h6>
<a name="id517417"></a>
            <a href="value_at.html#fusion.sequences.intrinsics.metafunctions.value_at.synopsis">Synopsis</a>
          </h6>
<pre class="programlisting">
<span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <span class="identifier">Seq</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">N</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">value_at</span>
<span class="special">{</span>
    <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span> <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>
</pre>
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<h4>
<a name="id517539"></a>
              <span class="table-title">Parameters</span>
            </h4>
<table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Parameter</th>
<th>Requirement</th>
<th>Description</th>
</tr></thead>
<tbody>
<tr>
<td><tt class="computeroutput"><span class="identifier">Seq</span></tt></td>
<td>A
                  model of <a href="../../concepts/forward_sequence.html" title="Forward
        Sequence">Forward
                  Sequence</a>
</td>
<td>Argument sequence</td>
</tr>
<tr>
<td><tt class="computeroutput"><span class="identifier">N</span></tt></td>
<td>An
                  MPL Integral Constant</td>
<td>Index of element</td>
</tr>
</tbody>
</table>
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<a name="fusion.sequences.intrinsics.metafunctions.value_at.expression_semantics"></a><h6>
<a name="id517636"></a>
            <a href="value_at.html#fusion.sequences.intrinsics.metafunctions.value_at.expression_semantics">Expression
            Semantics</a>
          </h6>
<pre class="programlisting">
<span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at</span><span class="special">&lt;</span><span class="identifier">Seq</span><span class="special">,</span> <span class="identifier">N</span><span class="special">&gt;::</span><span class="identifier">type</span>
</pre>
<p>
            <span class="bold"><b>Return type</b></span>: Any type.
          </p>
<p>
            <span class="bold"><b>Semantics</b></span>: Returns the actual type at
            the <tt class="computeroutput"><span class="identifier">N</span></tt>th element of <tt class="computeroutput"><span class="identifier">Seq</span></tt>.
          </p>
<a name="fusion.sequences.intrinsics.metafunctions.value_at.header"></a><h6>
<a name="id517759"></a>
            <a href="value_at.html#fusion.sequences.intrinsics.metafunctions.value_at.header">Header</a>
          </h6>
<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">value_at</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<a name="fusion.sequences.intrinsics.metafunctions.value_at.example"></a><h6>
<a name="id517865"></a>
            <a href="value_at.html#fusion.sequences.intrinsics.metafunctions.value_at.example">Example</a>
          </h6>
<pre class="programlisting">
<span class="keyword">typedef</span> <a href="../../containers/vector.html" title="vector"><tt class="computeroutput"><span class="identifier">vector</span></tt></a><span class="special">&lt;</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">&gt;</span> <span class="identifier">vec</span><span class="special">;</span>
<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">&lt;</span><a href="value_at.html" title="value_at"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at</span></tt></a><span class="special">&lt;</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">&lt;</span><span class="number">1</span><span class="special">&gt;</span> <span class="special">&gt;::</span><span class="identifier">type</span><span class="special">,</span> <span class="keyword">float</span><span class="special">&gt;));</span>
</pre>
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