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boost_fusion/doc/html/fusion/sequence/intrinsic/functions/front.html
Joel de Guzman e9fd448376 fixed documentation bug 
[SVN r42116]
2007-12-17 09:27:42 +00:00

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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>front</title>
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<link rel="start" href="../../../../index.html" title="Chapter 1. Fusion 2.0">
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<div class="section" lang="en">
<div class="titlepage"><div><div><h5 class="title">
<a name="fusion.sequence.intrinsic.functions.front"></a><a href="front.html" title="front">front</a></h5></div></div></div>
<a name="fusion.sequence.intrinsic.functions.front.description"></a><h6>
<a name="id500670"></a>
<a href="front.html#fusion.sequence.intrinsic.functions.front.description">Description</a>
</h6>
<p>
Returns the first element in the sequence.
</p>
<a name="fusion.sequence.intrinsic.functions.front.synopsis"></a><h6>
<a name="id500701"></a>
<a href="front.html#fusion.sequence.intrinsic.functions.front.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">Sequence</span><span class="special">&gt;</span>
<span class="keyword">typename</span> <a href="../metafunctions/front.html" title="front"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">front</span></tt></a><span class="special">&lt;</span><span class="identifier">Sequence</span><span class="special">&gt;::</span><span class="identifier">type</span>
<span class="identifier">front</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">Sequence</span><span class="special">&gt;</span>
<span class="keyword">typename</span> <a href="../metafunctions/front.html" title="front"><tt class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">front</span></tt></a><span class="special">&lt;</span><span class="identifier">Sequence</span> <span class="keyword">const</span><span class="special">&gt;::</span><span class="identifier">type</span>
<span class="identifier">front</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.sequence.intrinsic.functions.front.parameters"></a><h6>
<a name="id500978"></a>
<a href="front.html#fusion.sequence.intrinsic.functions.front.parameters">Parameters</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Requirement
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody><tr>
<td>
<p>
<tt class="computeroutput"><span class="identifier">seq</span></tt>
</p>
</td>
<td>
<p>
Model of <a href="../../concepts/forward_sequence.html" title="Forward
Sequence">Forward
Sequence</a>
</p>
</td>
<td>
<p>
The sequence we wish to investigate.
</p>
</td>
</tr></tbody>
</table></div>
<a name="fusion.sequence.intrinsic.functions.front.expression_semantics"></a><h6>
<a name="id501092"></a>
<a href="front.html#fusion.sequence.intrinsic.functions.front.expression_semantics">Expression
Semantics</a>
</h6>
<pre class="programlisting">
<span class="identifier">front</span><span class="special">(</span><span class="identifier">seq</span><span class="special">);</span>
</pre>
<p>
<span class="bold"><b>Return type</b></span>: Returns a reference to
the first element in the sequence <tt class="computeroutput"><span class="identifier">seq</span></tt>
if <tt class="computeroutput"><span class="identifier">seq</span></tt> is mutable and
<tt class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
<span class="identifier">o</span></tt>, where <tt class="computeroutput"><span class="identifier">e</span></tt>
is the first element in the sequence, is a valid expression. Else, returns
a type convertable to the first element in the sequence.
</p>
<p>
<span class="bold"><b>Precondition</b></span>: <tt class="computeroutput"><a href="empty.html" title="empty"><tt class="computeroutput"><span class="identifier">empty</span></tt></a><span class="special">(</span><span class="identifier">seq</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">false</span></tt>
</p>
<p>
<span class="bold"><b>Semantics</b></span>: Returns the first element
in the sequence.
</p>
<a name="fusion.sequence.intrinsic.functions.front.header"></a><h6>
<a name="id501292"></a>
<a href="front.html#fusion.sequence.intrinsic.functions.front.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">front</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<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">include</span><span class="special">/</span><span class="identifier">front</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<a name="fusion.sequence.intrinsic.functions.front.example"></a><h6>
<a name="id501461"></a>
<a href="front.html#fusion.sequence.intrinsic.functions.front.example">Example</a>
</h6>
<pre class="programlisting">
<a href="../../../container/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">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">v</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">);</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">front</span><span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
</pre>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2007 Joel de Guzman, Dan Marsden, Tobias
Schwinger<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
</p>
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