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

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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_typetraits.reference.is_constructible"></a><a class="link" href="is_constructible.html" title="is_constructible">is_constructible</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">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span>
  30 <span class="keyword">struct</span> <span class="identifier">is_constructible</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 <code class="computeroutput"><span class="identifier">T</span></code>
  34         can be constructed from <code class="computeroutput"><span class="identifier">Args</span></code>,
  35         then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
  36         otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
  37         Type <code class="computeroutput"><span class="identifier">T</span></code> must be a complete
  38         type.
  39       </p>
  40 <p>
  41         Formally the trait answers the question, is the expression:
  42       </p>
  43 <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">t</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">declval</span><span class="special">&lt;</span><span class="identifier">Args</span><span class="special">&gt;()...);</span>
  44 </pre>
  45 <p>
  46         valid?
  47       </p>
  48 <p>
  49         There are a number of important special cases for this trait:
  50       </p>
  51 <pre class="programlisting"><span class="identifier">is_constructible</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value</span>
  52 </pre>
  53 <p>
  54         Indicates whether <code class="computeroutput"><span class="identifier">T</span></code> is default
  55         constructible, while:
  56       </p>
  57 <pre class="programlisting"><span class="identifier">is_constructible</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;&gt;::</span><span class="identifier">value</span>
  58 </pre>
  59 <p>
  60         Indicates whether <code class="computeroutput"><span class="identifier">T</span></code> is copy-constructible,
  61         and:
  62       </p>
  63 <pre class="programlisting"><span class="identifier">is_constructible</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value</span>
  64 </pre>
  65 <p>
  66         Indicates whether <code class="computeroutput"><span class="identifier">T</span></code> is move-constructible.
  67       </p>
  68 <p>
  69         <span class="bold"><strong>Compiler Compatibility:</strong></span> This trait requires
  70         the C++11 features <code class="computeroutput"><span class="keyword">decltype</span></code>
  71         variadic templates and SFINAE-expression support for full support. While
  72         there is some fallback code for cases where this is not the case, the trait
  73         should really be considered broken in that case.
  74       </p>
  75 <p>
  76         <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
  77         <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_copy_constructible</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  78         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>
  79       </p>
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  84       Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant,
  85       Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten
  86       Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven
  87       Watanabe<p>
  88         Distributed under the Boost Software License, Version 1.0. (See accompanying
  89         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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