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  26 <a name="boost.contract.call_if__idm45123870909024"></a><div class="titlepage"></div>
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  28 <h2><span class="refentrytitle">Struct template call_if_statement&lt;true, Then, internal_type&gt;</span></h2>
  29 <p>boost::contract::call_if_statement&lt;true, Then, internal_type&gt; &#8212; Template specialization to dispatch between then-branch functor template calls that return void and the ones that return non-void. </p>
  30 </div>
  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><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Then<span class="special">&gt;</span>
  35 <span class="keyword">struct</span> <a class="link" href="call_if__idm45123870909024.html" title="Struct template call_if_statement&lt;true, Then, internal_type&gt;">call_if_statement</a><span class="special">&lt;</span><span class="keyword">true</span><span class="special">,</span> <span class="identifier">Then</span><span class="special">,</span> <span class="identifier">internal_type</span><span class="special">&gt;</span> <span class="special">:</span> <span class="keyword">public</span> boost::contract::call_if_statement&lt; true, Then, result_of&lt; Then()&gt;::type &gt;
  36 <span class="special">{</span>
  37   <span class="comment">// <a class="link" href="call_if__idm45123870909024.html#boost.contract.call_if__idm45123870909024construct-copy-destruct">construct/copy/destruct</a></span>
  38   <span class="keyword">explicit</span> <a class="link" href="call_if__idm45123870909024.html#idm45123870897376-bb"><span class="identifier">call_if_statement</span></a><span class="special">(</span><span class="identifier">Then</span><span class="special">)</span><span class="special">;</span>
  39 <span class="special">}</span><span class="special">;</span></pre></div>
  40 <div class="refsect1">
  41 <a name="idm45751731503840"></a><h2>Description</h2>
  42 <p>The base class is a call-if statement so the else and else-if statements can be specified if needed. Usually this class template is instantiated only via the return value of  <code class="computeroutput"><a class="link" href="call_if.html" title="Function template call_if">boost::contract::call_if</a></code> and <code class="computeroutput"><a class="link" href="call_if_c.html" title="Function template call_if_c">boost::contract::call_if_c</a></code>.</p>
  43 <div class="note"><table border="0" summary="Note">
  44 <tr>
  45 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
  46 <th align="left">Note</th>
  47 </tr>
  48 <tr><td align="left" valign="top"><p>The <code class="computeroutput">result_of&lt;Then()&gt;::type</code> expression should be evaluated only when the static predicate is already checked to be <code class="computeroutput">true</code> (because <code class="computeroutput">Then()</code> is required to compile only in that case). Thus, this template specialization introduces an extra level of indirection necessary for proper lazy evaluation of this result-of expression.</p></td></tr>
  49 </table></div>
  50 <p>
  51 </p>
  52 <p><span class="bold"><strong>See Also:</strong></span></p>
  53 <p> <a class="link" href="../../boost_contract/extras.html#boost_contract.extras.assertion_requirements__templates_" title="Assertion Requirements (Templates)">
  54         Assertion Requirements</a></p>
  55 <p>
  56 </p>
  57 <p>
  58
  59 </p>
  60 <div class="refsect2">
  61 <a name="idm45751731495248"></a><h3>Template Parameters</h3>
  62 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
  63 <pre class="literallayout"><span class="keyword">typename</span> Then</pre>
  64 <p>Type of functor template to call when the static predicate is <code class="computeroutput">true</code> (as it is for this template specialization). </p>
  65 </li></ol></div>
  66 </div>
  67 <div class="refsect2">
  68 <a name="idm45751731491376"></a><h3>
  69 <a name="boost.contract.call_if__idm45123870909024construct-copy-destruct"></a><code class="computeroutput">call_if_statement</code>
  70         public
  71        construct/copy/destruct</h3>
  72 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
  73 <pre class="literallayout"><span class="keyword">explicit</span> <a name="idm45123870897376-bb"></a><span class="identifier">call_if_statement</span><span class="special">(</span><span class="identifier">Then</span> f<span class="special">)</span><span class="special">;</span></pre>Construct this object with the then-branch functor template. <p>
  74 </p>
  75 <div class="variablelist"><table border="0" class="variablelist compact">
  76 <colgroup>
  77 <col align="left" valign="top">
  78 <col>
  79 </colgroup>
  80 <tbody><tr>
  81 <td><p><span class="term">Parameters:</span></p></td>
  82 <td><div class="variablelist"><table border="0" class="variablelist compact">
  83 <colgroup>
  84 <col align="left" valign="top">
  85 <col>
  86 </colgroup>
  87 <tbody><tr>
  88 <td><p><span class="term"><code class="computeroutput">f</code></span></p></td>
  89 <td><p>Then-branch nullary functor template. The functor template call <code class="computeroutput">f()</code> is compiled and called for this template specialization (because the if-statement static predicate is <code class="computeroutput">true</code>). The return type of <code class="computeroutput">f()</code> must be the same as (or implicitly convertible to) the return type of all other functor template calls specified for this call-if object. </p></td>
  90 </tr></tbody>
  91 </table></div></td>
  92 </tr></tbody>
  93 </table></div>
  94 </li></ol></div>
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 102         file LICENSE_1_0.txt or a copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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