ceph/src/boost/libs/type_traits/doc/html/boost_typetraits/reference/has_trivial_assign.html

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  27 <a name="boost_typetraits.reference.has_trivial_assign"></a><a class="link" href="has_trivial_assign.html" title="has_trivial_assign">has_trivial_assign</a>
  28 </h3></div></div></div>
  29 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
  30 <span class="keyword">struct</span> <span class="identifier">has_trivial_assign</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         type with a trivial assignment-operator 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         If a type has a trivial assignment-operator then the operator has the same
  39         effect as copying the bits of one object to the other: calls to the operator
  40         can be safely replaced with a call to <code class="computeroutput"><span class="identifier">memcpy</span></code>.
  41       </p>
  42 <p>
  43         <span class="bold"><strong>Compiler Compatibility:</strong></span> Without some (as
  44         yet unspecified) help from the compiler, has_trivial_assign will never report
  45         that a user-defined class or struct has a trivial constructor; this is always
  46         safe, if possibly sub-optimal. In order to correctly handle deleted or private
  47         assignment operators, the compiler must also support C++11's <code class="computeroutput"><span class="keyword">decltype</span></code>. Currently (May 2015) compilers more
  48         recent than Visual C++ 8, GCC-4.3, Greenhills 6.0, Intel-11.0, and Codegear
  49         have the necessary compiler <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a>
  50         to ensure that this trait "just works". You may also test to see
  51         if the necessary <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a>
  52         are available by checking to see if the macro <code class="computeroutput"><span class="identifier">BOOST_HAS_TRIVIAL_ASSIGN</span></code>
  53         is defined.
  54       </p>
  55 <p>
  56         <span class="bold"><strong>C++ Standard Reference:</strong></span> 12.8p11.
  57       </p>
  58 <p>
  59         <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
  60         <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">has_trivial_assign</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  61         or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</span></code>
  62       </p>
  63 <p>
  64         <span class="bold"><strong>Examples:</strong></span>
  65       </p>
  66 <div class="blockquote"><blockquote class="blockquote"><p>
  67           <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span></code>
  68           inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
  69         </p></blockquote></div>
  70 <div class="blockquote"><blockquote class="blockquote"><p>
  71           <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">*&gt;::</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>.
  72         </p></blockquote></div>
  73 <div class="blockquote"><blockquote class="blockquote"><p>
  74           <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special">&lt;</span><span class="keyword">int</span> <span class="special">(*)(</span><span class="keyword">long</span><span class="special">)&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
  75           that evaluates to <span class="emphasis"><em>true</em></span>.
  76         </p></blockquote></div>
  77 <div class="blockquote"><blockquote class="blockquote"><p>
  78           <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
  79           that evaluates to <span class="emphasis"><em>false</em></span>.
  80         </p></blockquote></div>
  81 <div class="blockquote"><blockquote class="blockquote"><p>
  82           <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value_type</span></code> is the type <code class="computeroutput"><span class="keyword">bool</span></code>.
  83         </p></blockquote></div>
  84 </div>
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  87 <td align="right"><div class="copyright-footer">Copyright &#169; 2000, 2011 Adobe Systems Inc, David Abrahams,
  88       Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant,
  89       Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten
  90       Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven
  91       Watanabe<p>
  92         Distributed under the Boost Software License, Version 1.0. (See accompanying
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