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| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h3 class="title"> | |
| 27 | <a name="boost_typetraits.reference.is_class"></a><a class="link" href="is_class.html" title="is_class">is_class</a> | |
| 28 | </h3></div></div></div> | |
| 29 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> | |
| 30 | <span class="keyword">struct</span> <span class="identifier">is_class</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span> | |
| 31 | </pre> | |
| 32 | <p> | |
| 33 | <span class="bold"><strong>Inherits:</strong></span> If T is a (possibly cv-qualified) | |
| 34 | class type (and not a union type) then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>, | |
| 35 | otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>. | |
| 36 | </p> | |
| 37 | <p> | |
| 38 | <span class="bold"><strong>C++ Standard Reference:</strong></span> 3.9.2 and 9.2. | |
| 39 | </p> | |
| 40 | <p> | |
| 41 | <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span> | |
| 42 | <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_class</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> | |
| 43 | or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> | |
| 44 | </p> | |
| 45 | <p> | |
| 46 | <span class="bold"><strong>Compiler Compatibility:</strong></span> This trait works | |
| 47 | correctly for almost all current compilers (as of June 2015), with just a | |
| 48 | minority of older compilers not correctly detecting all the corner cases. | |
| 49 | You can check the macro <code class="computeroutput"><span class="identifier">BOOST_TT_HAS_CONFORMING_IS_CLASS_IMPLEMENTATION</span></code> | |
| 50 | which is defined to 1 when the class works correctly in all cases. | |
| 51 | </p> | |
| 52 | <p> | |
| 53 | <span class="bold"><strong>Examples:</strong></span> | |
| 54 | </p> | |
| 55 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 56 | Given: <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">MyClass</span><span class="special">;</span></code> then: | |
| 57 | </p></blockquote></div> | |
| 58 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 59 | <code class="computeroutput"><span class="identifier">is_class</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span></code> | |
| 60 | inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. | |
| 61 | </p></blockquote></div> | |
| 62 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 63 | <code class="computeroutput"><span class="identifier">is_class</span><span class="special"><</span><span class="identifier">MyClass</span> <span class="keyword">const</span><span class="special">>::</span><span class="identifier">type</span></code> | |
| 64 | is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. | |
| 65 | </p></blockquote></div> | |
| 66 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 67 | <code class="computeroutput"><span class="identifier">is_class</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>::</span><span class="identifier">value</span></code> is an integral constant expression | |
| 68 | that evaluates to <span class="emphasis"><em>true</em></span>. | |
| 69 | </p></blockquote></div> | |
| 70 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 71 | <code class="computeroutput"><span class="identifier">is_class</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">&>::</span><span class="identifier">value</span></code> is an integral constant expression | |
| 72 | that evaluates to <span class="emphasis"><em>false</em></span>. | |
| 73 | </p></blockquote></div> | |
| 74 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 75 | <code class="computeroutput"><span class="identifier">is_class</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">*>::</span><span class="identifier">value</span></code> is an integral constant expression | |
| 76 | that evaluates to <span class="emphasis"><em>false</em></span>. | |
| 77 | </p></blockquote></div> | |
| 78 | <div class="blockquote"><blockquote class="blockquote"><p> | |
| 79 | <code class="computeroutput"><span class="identifier">is_class</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_type</span></code> is the type <code class="computeroutput"><span class="keyword">bool</span></code>. | |
| 80 | </p></blockquote></div> | |
| 81 | </div> | |
| 82 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 83 | <td align="left"></td> | |
| 84 | <td align="right"><div class="copyright-footer">Copyright © 2000, 2011 Adobe Systems Inc, David Abrahams, | |
| 85 | Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, | |
| 86 | Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten | |
| 87 | Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven | |
| 88 | Watanabe<p> | |
| 89 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 90 | file LICENSE_1_0.txt or 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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