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| <title>The MPL Reference Manual: eval_if_c</title> |
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| <div class="section" id="eval-if-c"> |
| <h1><a class="toc-backref" href="./type-selection.html#id1523">eval_if_c</a></h1> |
| <div class="section" id="id880"> |
| <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> |
| <pre class="literal-block"> |
| template< |
| bool c |
| , typename F1 |
| , typename F2 |
| > |
| struct <a href="./eval-if-c.html" class="identifier">eval_if_c</a> |
| { |
| typedef <em>unspecified</em> type; |
| }; |
| </pre> |
| </div> |
| <div class="section" id="id881"> |
| <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> |
| <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 |
| 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><c,f1,f2>::type</span></tt> is a shorcut |
| notation for <tt class="literal"><span class="pre"><a href="./eval-if.html" class="identifier">eval_if</a><</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a><c>,f1,f2</span> <span class="pre">>::type</span></tt>.</p> |
| </div> |
| <div class="section" id="id882"> |
| <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> |
| <pre class="literal-block"> |
| #include <<a href="../../../../boost/mpl/eval_if.hpp" class="header">boost/mpl/eval_if.hpp</a>> |
| </pre> |
| </div> |
| <div class="section" id="id883"> |
| <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> |
| <table border="1" class="docutils table"> |
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| <col width="36%" /> |
| <col width="48%" /> |
| </colgroup> |
| <thead valign="bottom"> |
| <tr><th class="head">Parameter</th> |
| <th class="head">Requirement</th> |
| <th class="head">Description</th> |
| </tr> |
| </thead> |
| <tbody valign="top"> |
| <tr><td><tt class="literal"><span class="pre">c</span></tt></td> |
| <td>An integral constant</td> |
| <td>An evaluation condition.</td> |
| </tr> |
| <tr><td><tt class="literal"><span class="pre">F1</span></tt>, <tt class="literal"><span class="pre">F2</span></tt></td> |
| <td>Nullary <a class="reference internal" href="./metafunction.html">Metafunction</a></td> |
| <td>Metafunctions to select for evaluation from.</td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| <div class="section" id="id884"> |
| <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> |
| <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> |
| <pre class="literal-block"> |
| typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a><c,f1,f2>::type t; |
| </pre> |
| <table class="docutils field-list" frame="void" rules="none"> |
| <col class="field-name" /> |
| <col class="field-body" /> |
| <tbody valign="top"> |
| <tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td> |
| </tr> |
| <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><</span> <span class="pre"><a href="./bool.html" class="identifier">bool_</a><c>,f1,f2</span> <span class="pre">>::type</span> <span class="pre">t;</span></tt></td> |
| </tr> |
| </tbody> |
| </table> |
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| <div class="section" id="id885"> |
| <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> |
| <pre class="literal-block"> |
| typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a>< true, <a href="./identity.html" class="identifier">identity</a><char>, <a href="./identity.html" class="identifier">identity</a><long> >::type t1; |
| typedef <a href="./eval-if-c.html" class="identifier">eval_if_c</a>< false, <a href="./identity.html" class="identifier">identity</a><char>, <a href="./identity.html" class="identifier">identity</a><long> >::type t2; |
| |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same<t1,char> )); |
| <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same<t2,long> )); |
| </pre> |
| </div> |
| <div class="section" id="id886"> |
| <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> |
| <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> |
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