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boost_fusion/doc/html/fusion/sequences/intrinsics/functions/at_key.html
Tobias Schwinger ca6f831b96 adds documentation for functional module 
[SVN r36959]
2007-02-15 23:11:24 +00:00

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<title>at_key</title>
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<div class="titlepage"><div><div><h5 class="title">
<a name="fusion.sequences.intrinsics.functions.at_key"></a><a href="at_key.html" title="at_key">at_key</a></h5></div></div></div>
<a name="fusion.sequences.intrinsics.functions.at_key.description"></a><h6>
<a name="id1010731"></a>
<a href="at_key.html#fusion.sequences.intrinsics.functions.at_key.description">Description</a>
</h6>
<p>
Returns the element associated with a Key from the sequence.
</p>
<a name="fusion.sequences.intrinsics.functions.at_key.synopsis"></a><h6>
<a name="id1010760"></a>
<a href="at_key.html#fusion.sequences.intrinsics.functions.at_key.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">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"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></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"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></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.sequences.intrinsics.functions.at_key.parameters"></a><h6>
<a name="id1011053"></a>
<a href="at_key.html#fusion.sequences.intrinsics.functions.at_key.parameters">Parameters</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Parameter</th>
<th>Requirement</th>
<th>Description</th>
</tr></thead>
<tbody>
<tr>
<td><code class="computeroutput"><span class="identifier">seq</span></code></td>
<td>Model
of <a href="../../concepts/associative_sequence.html" title="Associative
Sequence">Associative
Sequence</a>
</td>
<td>The sequence we wish to investigate.</td>
</tr>
<tr>
<td><code class="computeroutput"><span class="identifier">Key</span></code></td>
<td>Any
type</td>
<td>The queried key.</td>
</tr>
</tbody>
</table></div>
<a name="fusion.sequences.intrinsics.functions.at_key.expression_semantics"></a><h6>
<a name="id1011151"></a>
<a href="at_key.html#fusion.sequences.intrinsics.functions.at_key.expression_semantics">Expression
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"><strong>Return type</strong></span>: Returns a reference to
the element associated with Key from the sequence <code class="computeroutput"><span class="identifier">seq</span></code>
if <code class="computeroutput"><span class="identifier">seq</span></code> is mutable and
<code class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
<span class="identifier">o</span></code>, where <code class="computeroutput"><span class="identifier">e</span></code>
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"><strong>Precondition</strong></span>: <code 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></code>
</p>
<p>
<span class="bold"><strong>Semantics</strong></span>: Returns the element associated
with Key.
</p>
<a name="fusion.sequences.intrinsics.functions.at_key.header"></a><h6>
<a name="id1011328"></a>
<a href="at_key.html#fusion.sequences.intrinsics.functions.at_key.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">at_key</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<a name="fusion.sequences.intrinsics.functions.at_key.example"></a><h6>
<a name="id1011421"></a>
<a href="at_key.html#fusion.sequences.intrinsics.functions.at_key.example">Example</a>
</h6>
<pre class="programlisting">
<a href="../../containers/set.html" title="set"><code class="computeroutput"><span class="identifier">set</span></code></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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