ceph/src/boost/libs/mpl/doc/refmanual/eval-if-c.html

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  14 <div class="section" id="eval-if-c">
  15 <h1><a class="toc-backref" href="./type-selection.html#id1523">eval_if_c</a></h1>
  16 <div class="section" id="id880">
  17 <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
  18 <pre class="literal-block">
  19 template&lt;
  20       bool c
  21     , typename F1
  22     , typename F2
  23     &gt;
  24 struct <a href="./eval-if-c.html" class="identifier">eval_if_c</a>
  25 {
  26     typedef <em>unspecified</em> type;
  27 };
  28 </pre>
  29 </div>
  30 <div class="section" id="id881">
  31 <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
  32 <p>Evaluates one of its two <a class="reference internal" href="./metafunction.html#nullary-metafunction">nullary-metafunction</a> arguments, <tt class="literal"><span class="pre">F1</span></tt> or <tt class="literal"><span class="pre">F2</span></tt>, depending
  33 on the value of integral constant <tt class="literal"><span class="pre">c</span></tt>. <tt class="literal"><span class="pre"><a href="./eval-if-c.html" class="identifier">eval_if_c</a>&lt;c,f1,f2&gt;::type</span></tt> is a shorcut
  34 notation for <tt class="literal"><span class="pre"><a href="./eval-if.html" class="identifier">eval_if</a>&lt;</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a>&lt;c&gt;,f1,f2</span> <span class="pre">&gt;::type</span></tt>.</p>
  35 </div>
  36 <div class="section" id="id882">
  37 <h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
  38 <pre class="literal-block">
  39 #include &lt;<a href="../../../../boost/mpl/eval_if.hpp" class="header">boost/mpl/eval_if.hpp</a>&gt;
  40 </pre>
  41 </div>
  42 <div class="section" id="id883">
  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="15%" />
  47 <col width="36%" />
  48 <col width="48%" />
  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">c</span></tt></td>
  58 <td>An integral constant</td>
  59 <td>An evaluation condition.</td>
  60 </tr>
  61 <tr><td><tt class="literal"><span class="pre">F1</span></tt>, <tt class="literal"><span class="pre">F2</span></tt></td>
  62 <td>Nullary <a class="reference internal" href="./metafunction.html">Metafunction</a></td>
  63 <td>Metafunctions to select for evaluation from.</td>
  64 </tr>
  65 </tbody>
  66 </table>
  67 </div>
  68 <div class="section" id="id884">
  69 <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
  70 <p>For any integral constant <tt class="literal"><span class="pre">c</span></tt> and nullary <a class="reference internal" href="./metafunction.html">Metafunction</a>s <tt class="literal"><span class="pre">f1</span></tt>, <tt class="literal"><span class="pre">f2</span></tt>:</p>
  71 <pre class="literal-block">
  72 typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a>&lt;c,f1,f2&gt;::type t;
  73 </pre>
  74 <table class="docutils field-list" frame="void" rules="none">
  75 <col class="field-name" />
  76 <col class="field-body" />
  77 <tbody valign="top">
  78 <tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td>
  79 </tr>
  80 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body">Equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre"><a href="./eval-if.html" class="identifier">eval_if</a>&lt;</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a>&lt;c&gt;,f1,f2</span> <span class="pre">&gt;::type</span> <span class="pre">t;</span></tt></td>
  81 </tr>
  82 </tbody>
  83 </table>
  84 </div>
  85 <div class="section" id="id885">
  86 <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
  87 <pre class="literal-block">
  88 typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a>&lt; true, <a href="./identity.html" class="identifier">identity</a>&lt;char&gt;, <a href="./identity.html" class="identifier">identity</a>&lt;long&gt; &gt;::type t1;
  89 typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a>&lt; false, <a href="./identity.html" class="identifier">identity</a>&lt;char&gt;, <a href="./identity.html" class="identifier">identity</a>&lt;long&gt; &gt;::type t2;
  90
  91 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;t1,char&gt; ));
  92 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;t2,long&gt; ));
  93 </pre>
  94 </div>
  95 <div class="section" id="id886">
  96 <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
  97 <p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./integral-constant.html">Integral Constant</a>, <a class="reference internal" href="./eval-if.html">eval_if</a>, <a class="reference internal" href="./if.html">if_</a>, <a class="reference internal" href="./bool.html">bool_</a></p>
  98 </div>
  99 </div>
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