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  28 <h2><span class="refentrytitle">Function template condition_if_c</span></h2>
  29 <p>boost::contract::condition_if_c &#8212; Select compilation and execution of a boolean functor template condition using a static boolean predicate (not needed on C++17 compilers, use <code class="computeroutput">if constexpr</code> instead). </p>
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  31 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  32 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../reference.html#header.boost.contract.call_if_hpp" title="Header &lt;boost/contract/call_if.hpp&gt;">boost/contract/call_if.hpp</a>&gt;
  33
  34 </span>
  35 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">bool</span> Pred<span class="special">,</span> <span class="keyword">typename</span> Then<span class="special">&gt;</span>
  36   <span class="keyword">bool</span> <span class="identifier">condition_if_c</span><span class="special">(</span><span class="identifier">Then</span> f<span class="special">,</span> <span class="keyword">bool</span> else_ <span class="special">=</span> <span class="keyword">true</span><span class="special">)</span><span class="special">;</span></pre></div>
  37 <div class="refsect1">
  38 <a name="idm45707997597920"></a><h2>Description</h2>
  39 <p>Compile and execute the nullary boolean functor template call <code class="computeroutput">f()</code> if and only if the specified static boolean predicate <code class="computeroutput">Pred</code> is <code class="computeroutput">true</code>, otherwise trivially return <code class="computeroutput">else_</code> (<code class="computeroutput">true</code> by default) at run-time.</p>
  40 <p>A call to <code class="computeroutput">boost::contract::condition_if_c&lt;Pred&gt;(f, else_)</code> is logically equivalent to <code class="computeroutput">boost::contract::call_if_c&lt;Pred&gt;(f, [] { return else_; })</code> (but its internal implementation is optimized and it does not actually use <code class="computeroutput">call_if_c</code>).</p>
  41 <p><span class="bold"><strong>See Also:</strong></span></p>
  42 <p> <a class="link" href="../../boost_contract/extras.html#boost_contract.extras.assertion_requirements__templates_" title="Assertion Requirements (Templates)">
  43         Assertion Requirements</a></p>
  44 <p>
  45 </p>
  46 <p>
  47
  48
  49
  50
  51 </p>
  52 <div class="variablelist"><table border="0" class="variablelist compact">
  53 <colgroup>
  54 <col align="left" valign="top">
  55 <col>
  56 </colgroup>
  57 <tbody>
  58 <tr>
  59 <td><p><span class="term">Parameters:</span></p></td>
  60 <td><div class="variablelist"><table border="0" class="variablelist compact">
  61 <colgroup>
  62 <col align="left" valign="top">
  63 <col>
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  67 <td><p><span class="term"><code class="computeroutput">else_</code></span></p></td>
  68 <td><p>Boolean value to return when <code class="computeroutput">Pred</code> is <code class="computeroutput">false</code> (instead of compiling and executing the functor template call <code class="computeroutput">f()</code>).</p></td>
  69 </tr>
  70 <tr>
  71 <td><p><span class="term"><code class="computeroutput">f</code></span></p></td>
  72 <td><p>Nullary boolean functor template. The functor template call <code class="computeroutput">f()</code> is compiled and executed if and only if <code class="computeroutput">Pred</code> is <code class="computeroutput">true</code>.</p></td>
  73 </tr>
  74 </tbody>
  75 </table></div></td>
  76 </tr>
  77 <tr>
  78 <td><p><span class="term">Template Parameters:</span></p></td>
  79 <td><div class="variablelist"><table border="0" class="variablelist compact">
  80 <colgroup>
  81 <col align="left" valign="top">
  82 <col>
  83 </colgroup>
  84 <tbody><tr>
  85 <td><p><span class="term"><code class="computeroutput">Pred</code></span></p></td>
  86 <td><p>Static boolean predicate selecting when the functor template call <code class="computeroutput">f()</code> should be compiled and executed. </p></td>
  87 </tr></tbody>
  88 </table></div></td>
  89 </tr>
  90 <tr>
  91 <td><p><span class="term">Returns:</span></p></td>
  92 <td><p>Boolean value returned by <code class="computeroutput">f()</code> if the static predicate <code class="computeroutput">Pred</code> is <code class="computeroutput">true</code>. Otherwise, trivially return <code class="computeroutput">else_</code>. </p></td>
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