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

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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_typetraits.reference.has_trivial_copy"></a><a class="link" href="has_trivial_copy.html" title="has_trivial_copy">has_trivial_copy</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_copy</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
  32 <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>
  33 <span class="keyword">struct</span> <span class="identifier">has_trivial_copy_constructor</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>
  34 </pre>
  35 <p>
  36         <span class="bold"><strong>Inherits:</strong></span> If T is a (possibly cv-qualified)
  37         type with a trivial copy-constructor then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
  38         otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
  39       </p>
  40 <p>
  41         These two traits are synonyms for each other.
  42       </p>
  43 <p>
  44         If a type has a trivial copy-constructor then the constructor has the same
  45         effect as copying the bits of one object to the other: calls to the constructor
  46         can be safely replaced with a call to <code class="computeroutput"><span class="identifier">memcpy</span></code>.
  47       </p>
  48 <p>
  49         <span class="bold"><strong>Compiler Compatibility:</strong></span> Without some (as
  50         yet unspecified) help from the compiler, has_trivial_copy will never report
  51         that a user-defined class or struct has a trivial constructor; this is always
  52         safe, if possibly sub-optimal. In addition, in order to correctly handle
  53         deleted or private copy-constructors then C++11's <code class="computeroutput"><span class="identifier">dectype</span></code>
  54         is required. Currently (May 2015) compilers more recent than Visual C++ 8,
  55         GCC-4.3, Greenhills 6.0, Intel-11.0, and Codegear have the necessary compiler
  56         <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a> to ensure that
  57         this trait "just works". You may also test to see if the necessary
  58         <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a> are available
  59         by checking to see if the macro <code class="computeroutput"><span class="identifier">BOOST_HAS_TRIVIAL_COPY</span></code>
  60         is defined.
  61       </p>
  62 <p>
  63         <span class="bold"><strong>C++ Standard Reference:</strong></span> 12.8p6.
  64       </p>
  65 <p>
  66         <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
  67         <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_copy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  68         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>
  69       </p>
  70 <p>
  71         <span class="bold"><strong>Examples:</strong></span>
  72       </p>
  73 <div class="blockquote"><blockquote class="blockquote"><p>
  74           <code class="computeroutput"><span class="identifier">has_trivial_copy</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span></code>
  75           inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
  76         </p></blockquote></div>
  77 <div class="blockquote"><blockquote class="blockquote"><p>
  78           <code class="computeroutput"><span class="identifier">has_trivial_copy</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>.
  79         </p></blockquote></div>
  80 <div class="blockquote"><blockquote class="blockquote"><p>
  81           <code class="computeroutput"><span class="identifier">has_trivial_copy</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
  82           that evaluates to <span class="emphasis"><em>true</em></span>.
  83         </p></blockquote></div>
  84 <div class="blockquote"><blockquote class="blockquote"><p>
  85           <code class="computeroutput"><span class="identifier">has_trivial_copy</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
  86           that evaluates to <span class="emphasis"><em>false</em></span>.
  87         </p></blockquote></div>
  88 <div class="blockquote"><blockquote class="blockquote"><p>
  89           <code class="computeroutput"><span class="identifier">has_trivial_copy</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>.
  90         </p></blockquote></div>
  91 </div>
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  95       Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant,
  96       Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten
  97       Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven
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