ceph/src/boost/libs/mpl/doc/refmanual/value-type.html

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   7 <title>The MPL Reference Manual: value_type</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="./value-type.html" class="navigation-link">value_type</a></td>
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  14 <div class="section" id="value-type">
  15 <h1><a class="toc-backref" href="./intrinsic-metafunctions.html#id1447">value_type</a></h1>
  16 <div class="section" id="id371">
  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     , typename X
  22     &gt;
  23 struct <a href="./value-type.html" class="identifier">value_type</a>
  24 {
  25     typedef <em>unspecified</em> type;
  26 };
  27 </pre>
  28 </div>
  29 <div class="section" id="id372">
  30 <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
  31 <p>Returns the <a class="reference internal" href="./associative-sequence.html#value-part">value</a> that would be used for element <tt class="literal"><span class="pre">X</span></tt> in <tt class="literal"><span class="pre">Sequence</span></tt>.</p>
  32 </div>
  33 <div class="section" id="id373">
  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/value_type.hpp" class="header">boost/mpl/value_type.hpp</a>&gt;
  37 </pre>
  38 </div>
  39 <div class="section" id="id374">
  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="id375">
  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="17%" />
  48 <col width="30%" />
  49 <col width="53%" />
  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">Sequence</span></tt></td>
  59 <td><a class="reference internal" href="./associative-sequence.html">Associative Sequence</a></td>
  60 <td>A sequence to query.</td>
  61 </tr>
  62 <tr><td><tt class="literal"><span class="pre">X</span></tt></td>
  63 <td>Any type</td>
  64 <td>The type to get the <a class="reference internal" href="./associative-sequence.html#value-part">value</a> for.</td>
  65 </tr>
  66 </tbody>
  67 </table>
  68 </div>
  69 <div class="section" id="id376">
  70 <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
  71 <p>For any <a class="reference internal" href="./associative-sequence.html">Associative Sequence</a> <tt class="literal"><span class="pre">s</span></tt>, and an artibrary type <tt class="literal"><span class="pre">x</span></tt>:</p>
  72 <pre class="literal-block">
  73 typedef <a href="./value-type.html" class="identifier">value_type</a>&lt;s,x&gt;::type v;
  74 </pre>
  75 <table class="docutils field-list" frame="void" rules="none">
  76 <col class="field-name" />
  77 <col class="field-body" />
  78 <tbody valign="top">
  79 <tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">A type.</p>
  80 </td>
  81 </tr>
  82 <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><p class="first"><tt class="literal"><span class="pre">x</span></tt> can be put in <tt class="literal"><span class="pre">s</span></tt>.</p>
  83 </td>
  84 </tr>
  85 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first"><tt class="literal"><span class="pre">v</span></tt> is the <a class="reference internal" href="./associative-sequence.html#value-part">value</a> that would be used for <tt class="literal"><span class="pre">x</span></tt> in <tt class="literal"><span class="pre">s</span></tt>.</p>
  86 </td>
  87 </tr>
  88 <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><p class="first">If
  89 .. parsed-literal:</p>
  90 <pre class="literal-block">
  91 <a href="./has-key.html" class="identifier">has_key</a>&lt; s,<a href="./key-type.html" class="identifier">key_type</a>&lt;s,x&gt;::type &gt;::type
  92 </pre>
  93 <p>then
  94 .. parsed-literal:</p>
  95 <pre class="literal-block">
  96 <a href="./at.html" class="identifier">at</a>&lt; s,<a href="./key-type.html" class="identifier">key_type</a>&lt;s,x&gt;::type &gt;::type
  97 </pre>
  98 <p class="last">is identical to <tt class="literal"><span class="pre"><a href="./value-type.html" class="identifier">value_type</a>&lt;s,x&gt;::type</span></tt>.</p>
  99 </td>
 100 </tr>
 101 </tbody>
 102 </table>
 103 </div>
 104 <div class="section" id="id377">
 105 <h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
 106 <p>Amortized constant time.</p>
 107 </div>
 108 <div class="section" id="id378">
 109 <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
 110 <pre class="literal-block">
 111 typedef <a href="./value-type.html" class="identifier">value_type</a>&lt; <a href="./map.html" class="identifier">map</a>&lt;&gt;,<a href="./pair.html" class="identifier">pair</a>&lt;int,unsigned&gt; &gt;::type v1;
 112 typedef <a href="./value-type.html" class="identifier">value_type</a>&lt; <a href="./set.html" class="identifier">set</a>&lt;&gt;,<a href="./pair.html" class="identifier">pair</a>&lt;int,unsigned&gt; &gt;::type v2;
 113
 114 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; v1,unsigned &gt; ));
 115 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt; v2,<a href="./pair.html" class="identifier">pair</a>&lt;int,unsigned&gt; > ));
 116 </pre>
 117 </div>
 118 <div class="section" id="id379">
 119 <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
 120 <p><a class="reference internal" href="./associative-sequence.html">Associative Sequence</a>, <a class="reference internal" href="./key-type.html">key_type</a>, <a class="reference internal" href="./at.html">at</a>, <a class="reference internal" href="./set.html">set</a>, <a class="reference internal" href="./map.html">map</a></p>
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