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

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   7 <title>The MPL Reference Manual: begin</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="./begin.html" class="navigation-link">begin</a></td>
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  14 <div class="section" id="begin">
  15 <h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1428">begin</a></h1>
  16 <div class="section" id="id202">
  17 <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
  18 <pre class="literal-block">
  19 template&lt;
  20       typename X
  21     &gt;
  22 struct <a href="./begin.html" class="identifier">begin</a>
  23 {
  24     typedef <em>unspecified</em> type;
  25 };
  26 </pre>
  27 </div>
  28 <div class="section" id="id203">
  29 <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
  30 <p>Returns an iterator that points to the first element of the sequence. If
  31 the argument is not a <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, returns <a class="reference internal" href="./void.html">void_</a>.</p>
  32 </div>
  33 <div class="section" id="id204">
  34 <h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
  35 <pre class="literal-block">
  36 #include &lt;<a href="../../../../boost/mpl/begin_end.hpp" class="header">boost/mpl/begin_end.hpp</a>&gt;
  37 </pre>
  38 </div>
  39 <div class="section" id="id205">
  40 <h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3>
  41 <p><a class="reference internal" href="./tag-dispatched-metafunction.html">Tag Dispatched Metafunction</a></p>
  42 </div>
  43 <div class="section" id="id206">
  44 <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
  45 <table border="1" class="docutils table">
  46 <colgroup>
  47 <col width="18%" />
  48 <col width="22%" />
  49 <col width="60%" />
  50 </colgroup>
  51 <thead valign="bottom">
  52 <tr><th class="head">Parameter</th>
  53 <th class="head">Requirement</th>
  54 <th class="head">Description</th>
  55 </tr>
  56 </thead>
  57 <tbody valign="top">
  58 <tr><td><tt class="literal"><span class="pre">X</span></tt></td>
  59 <td>Any type</td>
  60 <td>A type whose begin iterator, if any, will be
  61 returned.</td>
  62 </tr>
  63 </tbody>
  64 </table>
  65 </div>
  66 <div class="section" id="id207">
  67 <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
  68 <p>For any arbitrary type <tt class="literal"><span class="pre">x</span></tt>:</p>
  69 <pre class="literal-block">
  70 typedef <a href="./begin.html" class="identifier">begin</a>&lt;x&gt;::type first;
  71 </pre>
  72 <table class="docutils field-list" frame="void" rules="none">
  73 <col class="field-name" />
  74 <col class="field-body" />
  75 <tbody valign="top">
  76 <tr class="field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference internal" href="./forward-iterator.html">Forward Iterator</a> or <a class="reference internal" href="./void.html">void_</a>.</td>
  77 </tr>
  78 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body">If <tt class="literal"><span class="pre">x</span></tt> is a <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <tt class="literal"><span class="pre">first</span></tt> is an iterator pointing to the
  79 first element of <tt class="literal"><span class="pre">s</span></tt>; otherwise <tt class="literal"><span class="pre">first</span></tt> is <a class="reference internal" href="./void.html">void_</a>.</td>
  80 </tr>
  81 <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body">If <tt class="literal"><span class="pre">first</span></tt> is an iterator, it is either dereferenceable or past-the-end; it
  82 is past-the-end if and only if <tt class="literal"><span class="pre"><a href="./size.html" class="identifier">size</a>&lt;x&gt;::value</span> <span class="pre">==</span> <span class="pre">0</span></tt>.</td>
  83 </tr>
  84 </tbody>
  85 </table>
  86 </div>
  87 <div class="section" id="id208">
  88 <h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
  89 <p>Amortized constant time.</p>
  90 </div>
  91 <div class="section" id="id209">
  92 <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
  93 <pre class="literal-block">
  94 typedef <a href="./vector.html" class="identifier">vector</a>&lt; unsigned char,unsigned short,
  95     unsigned int,unsigned long &gt; unsigned_types;
  96
  97 typedef <a href="./begin.html" class="identifier">begin</a>&lt;unsigned_types&gt;::type iter;
  98 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./deref.html" class="identifier">deref</a>&lt;iter&gt;::type, unsigned char &gt; ));
  99
 100 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; <a href="./begin.html" class="identifier">begin</a>&lt;int&gt;::type, <a href="./void.html" class="identifier">void_</a> > ));
 101 </pre>
 102 </div>
 103 <div class="section" id="id210">
 104 <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
 105 <p><a class="reference internal" href="./iterators.html">Iterators</a>, <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference internal" href="./end.html">end</a>, <a class="reference internal" href="./size.html">size</a>, <a class="reference internal" href="./empty.html">empty</a></p>
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