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| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_typetraits.reference.is_union"></a><a class="link" href="is_union.html" title="is_union"> is_union</a> |
| </h3></div></div></div> |
| <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> |
| <span class="keyword">struct</span> <span class="identifier">is_union</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> |
| </pre> |
| <p> |
| <span class="bold"><strong>Inherits:</strong></span> If T is a (possibly cv-qualified) |
| union type then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>, |
| otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>. |
| Currently requires some kind of compiler support, otherwise unions are identified |
| as classes. |
| </p> |
| <p> |
| <span class="bold"><strong>C++ Standard Reference:</strong></span> 3.9.2 and 9.5. |
| </p> |
| <p> |
| <span class="bold"><strong>Compiler Compatibility:</strong></span> Without (some as |
| yet unspecified) help from the compiler, we cannot distinguish between union |
| and class types using only standard C++, as a result this type will never |
| inherit from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>, |
| unless the user explicitly specializes the template for their user-defined |
| union types, or unless the compiler supplies some unspecified intrinsic that |
| implements this functionality. Currently (May 2005) only Visual C++ 8 has |
| the necessary compiler <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a> |
| to make this trait "just work" without user intervention. |
| </p> |
| <p> |
| <span class="bold"><strong>Header:</strong></span> <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">is_union</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> |
| 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> |
| </p> |
| <p> |
| <span class="bold"><strong>Examples:</strong></span> |
| </p> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <code class="computeroutput"><span class="identifier">is_union</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span></code> |
| inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. |
| </p></blockquote></div> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <code class="computeroutput"><span class="identifier">is_union</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">void</span><span class="special">>::</span><span class="identifier">type</span></code> |
| is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. |
| </p></blockquote></div> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <code class="computeroutput"><span class="identifier">is_union</span><span class="special"><</span><span class="keyword">void</span><span class="special">>::</span><span class="identifier">value</span></code> is an integral constant expression |
| that evaluates to <span class="emphasis"><em>true</em></span>. |
| </p></blockquote></div> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <code class="computeroutput"><span class="identifier">is_union</span><span class="special"><</span><span class="keyword">void</span><span class="special">*>::</span><span class="identifier">value</span></code> is an integral constant expression |
| that evaluates to <span class="emphasis"><em>false</em></span>. |
| </p></blockquote></div> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <code class="computeroutput"><span class="identifier">is_union</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>. |
| </p></blockquote></div> |
| </div> |
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| <td align="right"><div class="copyright-footer">Copyright © 2000, 2006 Adobe Systems Inc, David Abrahams, |
| Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, Jesse Jones, Mat |
| Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert |
| Ramey and Jeremy Siek<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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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