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

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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_typetraits.reference.is_stateless"></a><a class="link" href="is_stateless.html" title="is_stateless">is_stateless</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">is_stateless</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 stateless type then
  34         inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
  35         otherwise from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
  36       </p>
  37 <p>
  38         Type T must be a complete type.
  39       </p>
  40 <p>
  41         A stateless type is a type that has no storage and whose constructors and
  42         destructors are trivial. That means that <code class="computeroutput"><span class="identifier">is_stateless</span></code>
  43         only inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>
  44         if the following expression is <code class="computeroutput"><span class="keyword">true</span></code>:
  45       </p>
  46 <pre class="programlisting"><span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">has_trivial_constructor</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value</span>
  47 <span class="special">&amp;&amp;</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><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</span>
  48 <span class="special">&amp;&amp;</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">has_trivial_destructor</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value</span>
  49 <span class="special">&amp;&amp;</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_class</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value</span>
  50 <span class="special">&amp;&amp;</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_empty</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value</span>
  51 </pre>
  52 <p>
  53         <span class="bold"><strong>C++ Standard Reference:</strong></span> 3.9p10.
  54       </p>
  55 <p>
  56         <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
  57         <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">is_stateless</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  58         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>
  59       </p>
  60 <p>
  61         <span class="bold"><strong>Compiler Compatibility:</strong></span> Without some (as
  62         yet unspecified) help from the compiler, is_stateless will never report that
  63         a class or struct is stateless; this is always safe, if possibly sub-optimal.
  64         Currently (June 2015) compilers more recent than Visual C++ 8, Clang, GCC-4.3,
  65         Greenhills 6.0, Intel-11.0, and Codegear have the necessary compiler <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a> to ensure that this
  66         trait "just works".
  67       </p>
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