ceph/src/boost/libs/mpl/doc/refmanual/front.html

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   7 <title>The MPL Reference Manual: front</title>
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  12 <td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./sequences.html" class="navigation-link">Sequences</a> / <a href="./intrinsic-metafunctions.html" class="navigation-link">Intrinsic Metafunctions</a> / <a href="./front.html" class="navigation-link">front</a></td>
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  14 <div class="section" id="front">
  15 <h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1434">front</a></h1>
  16 <div class="section" id="id256">
  17 <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
  18 <pre class="literal-block">
  19 template&lt;
  20       typename Sequence
  21     &gt;
  22 struct <a href="./front.html" class="identifier">front</a>
  23 {
  24     typedef <em>unspecified</em> type;
  25 };
  26 </pre>
  27 </div>
  28 <div class="section" id="id257">
  29 <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
  30 <p>Returns the first element in the sequence.</p>
  31 </div>
  32 <div class="section" id="id258">
  33 <h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
  34 <pre class="literal-block">
  35 #include &lt;<a href="../../../../boost/mpl/front.hpp" class="header">boost/mpl/front.hpp</a>&gt;
  36 </pre>
  37 </div>
  38 <div class="section" id="id259">
  39 <h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3>
  40 <p><a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a></p>
  41 </div>
  42 <div class="section" id="id260">
  43 <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
  44 <table border="1" class="docutils table">
  45 <colgroup>
  46 <col width="18%" />
  47 <col width="27%" />
  48 <col width="55%" />
  49 </colgroup>
  50 <thead valign="bottom">
  51 <tr><th class="head">Parameter</th>
  52 <th class="head">Requirement</th>
  53 <th class="head">Description</th>
  54 </tr>
  55 </thead>
  56 <tbody valign="top">
  57 <tr><td><tt class="literal"><span class="pre">Sequence</span></tt></td>
  58 <td><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a></td>
  59 <td>A sequence to be examined.</td>
  60 </tr>
  61 </tbody>
  62 </table>
  63 </div>
  64 <div class="section" id="id261">
  65 <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
  66 <p>For any <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> <tt class="literal"><span class="pre">s</span></tt>:</p>
  67 <pre class="literal-block">
  68 typedef <a href="./front.html" class="identifier">front</a>&lt;s&gt;::type t;
  69 </pre>
  70 <table class="docutils field-list" frame="void" rules="none">
  71 <col class="field-name" />
  72 <col class="field-body" />
  73 <tbody valign="top">
  74 <tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">A type.</p>
  75 </td>
  76 </tr>
  77 <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><p class="first"><tt class="literal"><span class="pre"><a href="./empty.html" class="identifier">empty</a>&lt;s&gt;::value</span> <span class="pre">==</span> <span class="pre">false</span></tt>.</p>
  78 </td>
  79 </tr>
  80 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
  81 <pre class="last literal-block">
  82 typedef <a href="./deref.html" class="identifier">deref</a>&lt; <a href="./begin.html" class="identifier">begin</a>&lt;s&gt;::type &gt;::type t;
  83 </pre>
  84 </td>
  85 </tr>
  86 </tbody>
  87 </table>
  88 </div>
  89 <div class="section" id="id262">
  90 <h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
  91 <p>Amortized constant time.</p>
  92 </div>
  93 <div class="section" id="id263">
  94 <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
  95 <pre class="literal-block">
  96 typedef <a href="./list.html" class="identifier">list</a>&lt;long&gt;::type types1;
  97 typedef <a href="./list.html" class="identifier">list</a>&lt;int,long&gt;::type types2;
  98 typedef <a href="./list.html" class="identifier">list</a>&lt;char,int,long&gt;::type types3;
  99
 100 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./front.html" class="identifier">front</a>&lt;types1&gt;::type, long &gt; ));
 101 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./front.html" class="identifier">front</a>&lt;types2&gt;::type, int&gt; ));
 102 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./front.html" class="identifier">front</a>&lt;types3&gt;::type, char&gt; ));
 103 </pre>
 104 </div>
 105 <div class="section" id="id264">
 106 <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
 107 <p><a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference internal" href="./back.html">back</a>, <a class="reference internal" href="./push-front.html">push_front</a>, <a class="reference internal" href="./begin.html">begin</a>, <a class="reference internal" href="./deref.html">deref</a>, <a class="reference internal" href="./at.html">at</a></p>
 108 <!-- Sequences/Intrinsic Metafunctions//has_key -->
 109 </div>
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 114 <td><div class="copyright-footer"><div class="copyright">Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams</div>
 115 Distributed under the Boost Software License, Version 1.0. (See accompanying
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