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  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="fusion.sequence.intrinsic.functions.front"></a><a class="link" href="front.html" title="front">front</a>
  28 </h5></div></div></div>
  29 <h6>
  30 <a name="fusion.sequence.intrinsic.functions.front.h0"></a>
  31             <span class="phrase"><a name="fusion.sequence.intrinsic.functions.front.description"></a></span><a class="link" href="front.html#fusion.sequence.intrinsic.functions.front.description">Description</a>
  32           </h6>
  33 <p>
  34             Returns the first element in the sequence.
  35           </p>
  36 <h6>
  37 <a name="fusion.sequence.intrinsic.functions.front.h1"></a>
  38             <span class="phrase"><a name="fusion.sequence.intrinsic.functions.front.synopsis"></a></span><a class="link" href="front.html#fusion.sequence.intrinsic.functions.front.synopsis">Synopsis</a>
  39           </h6>
  40 <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>
  41 <span class="keyword">typename</span> <a class="link" href="../metafunctions/front.html" title="front"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">front</span></code></a><span class="special">&lt;</span><span class="identifier">Sequence</span><span class="special">&gt;::</span><span class="identifier">type</span>
  42 <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>
  43
  44 <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>
  45 <span class="keyword">typename</span> <a class="link" href="../metafunctions/front.html" title="front"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">front</span></code></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>
  46 <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>
  47 </pre>
  48 <h6>
  49 <a name="fusion.sequence.intrinsic.functions.front.h2"></a>
  50             <span class="phrase"><a name="fusion.sequence.intrinsic.functions.front.parameters"></a></span><a class="link" href="front.html#fusion.sequence.intrinsic.functions.front.parameters">Parameters</a>
  51           </h6>
  52 <div class="informaltable"><table class="table">
  53 <colgroup>
  54 <col>
  55 <col>
  56 <col>
  57 </colgroup>
  58 <thead><tr>
  59 <th>
  60                     <p>
  61                       Parameter
  62                     </p>
  63                   </th>
  64 <th>
  65                     <p>
  66                       Requirement
  67                     </p>
  68                   </th>
  69 <th>
  70                     <p>
  71                       Description
  72                     </p>
  73                   </th>
  74 </tr></thead>
  75 <tbody><tr>
  76 <td>
  77                     <p>
  78                       <code class="computeroutput"><span class="identifier">seq</span></code>
  79                     </p>
  80                   </td>
  81 <td>
  82                     <p>
  83                       Model of <a class="link" href="../../concepts/forward_sequence.html" title="Forward Sequence">Forward
  84                       Sequence</a>
  85                     </p>
  86                   </td>
  87 <td>
  88                     <p>
  89                       The sequence we wish to investigate.
  90                     </p>
  91                   </td>
  92 </tr></tbody>
  93 </table></div>
  94 <h6>
  95 <a name="fusion.sequence.intrinsic.functions.front.h3"></a>
  96             <span class="phrase"><a name="fusion.sequence.intrinsic.functions.front.expression_semantics"></a></span><a class="link" href="front.html#fusion.sequence.intrinsic.functions.front.expression_semantics">Expression
  97             Semantics</a>
  98           </h6>
  99 <pre class="programlisting"><span class="identifier">front</span><span class="special">(</span><span class="identifier">seq</span><span class="special">);</span>
 100 </pre>
 101 <p>
 102             <span class="bold"><strong>Return type</strong></span>: Returns a reference to
 103             the first element in the sequence <code class="computeroutput"><span class="identifier">seq</span></code>
 104             if <code class="computeroutput"><span class="identifier">seq</span></code> is mutable and
 105             <code class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
 106             <span class="identifier">o</span></code>, where <code class="computeroutput"><span class="identifier">e</span></code>
 107             is the first element in the sequence, is a valid expression. Else, returns
 108             a type convertable to the first element in the sequence.
 109           </p>
 110 <p>
 111             <span class="bold"><strong>Precondition</strong></span>: <code class="computeroutput"><a class="link" href="empty.html" title="empty"><code class="computeroutput"><span class="identifier">empty</span></code></a><span class="special">(</span><span class="identifier">seq</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">false</span></code>
 112           </p>
 113 <p>
 114             <span class="bold"><strong>Semantics</strong></span>: Returns the first element
 115             in the sequence.
 116           </p>
 117 <h6>
 118 <a name="fusion.sequence.intrinsic.functions.front.h4"></a>
 119             <span class="phrase"><a name="fusion.sequence.intrinsic.functions.front.header"></a></span><a class="link" href="front.html#fusion.sequence.intrinsic.functions.front.header">Header</a>
 120           </h6>
 121 <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>
 122 <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>
 123 </pre>
 124 <h6>
 125 <a name="fusion.sequence.intrinsic.functions.front.h5"></a>
 126             <span class="phrase"><a name="fusion.sequence.intrinsic.functions.front.example"></a></span><a class="link" href="front.html#fusion.sequence.intrinsic.functions.front.example">Example</a>
 127           </h6>
 128 <pre class="programlisting"><a class="link" href="../../../container/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></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>
 129 <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>
 130 </pre>
 131 </div>
 132 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 133 <td align="left"></td>
 134 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2006, 2011, 2012 Joel de Guzman,
 135       Dan Marsden, Tobias Schwinger<p>
 136         Distributed under the Boost Software License, Version 1.0. (See accompanying
 137         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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