ceph/src/boost/libs/mpl/doc/refmanual/apply-wrap.html

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   7 <title>The MPL Reference Manual: apply_wrap</title>
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  12 <td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./metafunctions.html" class="navigation-link">Metafunctions</a> / <a href="./invocation.html" class="navigation-link">Invocation</a> / <a href="./apply-wrap.html" class="navigation-link">apply_wrap</a></td>
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  14 <div class="section" id="apply-wrap">
  15 <h1><a class="toc-backref" href="./invocation.html#id1526">apply_wrap</a></h1>
  16 <div class="section" id="id894">
  17 <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
  18 <pre class="literal-block">
  19 template&lt;
  20       typename F
  21     &gt;
  22 struct apply_wrap0
  23 {
  24     typedef <em>unspecified</em> type;
  25 };
  26
  27 template&lt;
  28       typename F, typename A1
  29     &gt;
  30 struct apply_wrap1
  31 {
  32     typedef <em>unspecified</em> type;
  33 };
  34
  35 <em>...</em>
  36
  37 template&lt;
  38       typename F, typename A1,<em>...</em> typename An
  39     &gt;
  40 struct <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>
  41 {
  42     typedef <em>unspecified</em> type;
  43 };
  44 </pre>
  45 </div>
  46 <div class="section" id="id895">
  47 <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
  48 <p>Invokes a <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a> <tt class="literal"><span class="pre">F</span></tt> with arguments <tt class="literal"><span class="pre">A1</span></tt>,... <tt class="literal"><span class="pre">An</span></tt>.</p>
  49 <p>In essence, <tt class="literal"><span class="pre"><a href="./apply-wrap.html" class="identifier">apply_wrap</a></span></tt> forms are nothing more than syntactic wrappers around
  50 <tt class="literal"><span class="pre">F::<a href="./apply.html" class="identifier">apply</a>&lt;A1,...</span> <span class="pre">An&gt;::type</span></tt> / <tt class="literal"><span class="pre">F::<a href="./apply.html" class="identifier">apply</a>::type</span></tt> expressions (hence the name).
  51 They provide a more concise notation and higher portability than their
  52 underlaying constructs at the cost of an extra template instantiation.</p>
  53 </div>
  54 <div class="section" id="id896">
  55 <h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
  56 <pre class="literal-block">
  57 #include &lt;<a href="../../../../boost/mpl/apply_wrap.hpp" class="header">boost/mpl/apply_wrap.hpp</a>&gt;
  58 </pre>
  59 </div>
  60 <div class="section" id="id897">
  61 <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
  62 <table border="1" class="docutils table">
  63 <colgroup>
  64 <col width="15%" />
  65 <col width="36%" />
  66 <col width="48%" />
  67 </colgroup>
  68 <thead valign="bottom">
  69 <tr><th class="head">Parameter</th>
  70 <th class="head">Requirement</th>
  71 <th class="head">Description</th>
  72 </tr>
  73 </thead>
  74 <tbody valign="top">
  75 <tr><td><tt class="literal"><span class="pre">F</span></tt></td>
  76 <td><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a></td>
  77 <td>A metafunction class to invoke.</td>
  78 </tr>
  79 <tr><td><tt class="literal"><span class="pre">A1</span></tt>,... <tt class="literal"><span class="pre">An</span></tt></td>
  80 <td>Any type</td>
  81 <td>Invocation arguments.</td>
  82 </tr>
  83 </tbody>
  84 </table>
  85 </div>
  86 <div class="section" id="id898">
  87 <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
  88 <p>For any <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a> <tt class="literal"><span class="pre">f</span></tt> and arbitrary types <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>:</p>
  89 <pre class="literal-block">
  90 typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>&lt;f,a1,<em>...</em>an&gt;::type t;
  91 </pre>
  92 <table class="docutils field-list" frame="void" rules="none">
  93 <col class="field-name" />
  94 <col class="field-body" />
  95 <tbody valign="top">
  96 <tr class="field"><th class="field-name">Return type:</th><td class="field-body">Any type.</td>
  97 </tr>
  98 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body">If <tt class="literal"><span class="pre">n</span> <span class="pre">&gt;</span> <span class="pre">0</span></tt>, equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre">f::<a href="./apply.html" class="identifier">apply</a>&lt;a1,...</span> <span class="pre">an&gt;::type</span> <span class="pre">t;</span></tt>,
  99 otherwise equivalent to either <tt class="literal"><span class="pre">typedef</span> <span class="pre">f::<a href="./apply.html" class="identifier">apply</a>::type</span> <span class="pre">t;</span></tt> or
 100 <tt class="literal"><span class="pre">typedef</span> <span class="pre">f::<a href="./apply.html" class="identifier">apply</a>&lt;&gt;::type</span> <span class="pre">t;</span></tt> depending on whether <tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a></span></tt> is
 101 a class or a class template.</td>
 102 </tr>
 103 </tbody>
 104 </table>
 105 </div>
 106 <div class="section" id="id899">
 107 <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
 108 <pre class="literal-block">
 109 struct f0
 110 {
 111     template&lt; typename T = int &gt; struct <a href="./apply.html" class="identifier">apply</a>
 112     {
 113         typedef char type;
 114     };
 115 };
 116
 117 struct g0
 118 {
 119     struct <a href="./apply.html" class="identifier">apply</a> { typedef char type; };
 120 };
 121
 122 struct f2
 123 {
 124     template&lt; typename T1, typename T2 &gt; struct <a href="./apply.html" class="identifier">apply</a>
 125     {
 126         typedef T2 type;
 127     };
 128 };
 129
 130
 131 typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">0</span></tt>&lt; f0 &gt;::type r1;
 132 typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">0</span></tt>&lt; g0 &gt;::type r2;
 133 typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">2</span></tt>&lt; f2,int,char &gt;::type r3;
 134
 135 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r1,char&gt; ));
 136 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r2,char&gt; ));
 137 <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same&lt;r3,char&gt; ));
 138 </pre>
 139 </div>
 140 <div class="section" id="id900">
 141 <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
 142 <p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./invocation.html">invocation</a>, <a class="reference internal" href="./apply.html">apply</a>, <a class="reference internal" href="./lambda.html">lambda</a>, <a class="reference internal" href="./quote.html">quote</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./protect.html">protect</a></p>
 143 <!-- Metafunctions/Invocation//unpack_args |30 -->
 144 </div>
 145 </div>
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 149 <td><div class="copyright-footer"><div class="copyright">Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams</div>
 150 Distributed under the Boost Software License, Version 1.0. (See accompanying
 151 file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body>
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