ceph/src/boost/libs/mpl/doc/refmanual/metafunction.html

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   7 <title>The MPL Reference Manual: Metafunction</title>
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  11 <table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Prev</a>&nbsp;<a href="./metafunction-class.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group">Back&nbsp;<a href="./metafunction-class.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Up</a>&nbsp;<a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
  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="./metafunctions-concepts.html" class="navigation-link">Concepts</a> / <a href="./metafunction.html" class="navigation-link">Metafunction</a></td>
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  14 <div class="section" id="metafunction">
  15 <h1><a class="toc-backref" href="./metafunctions-concepts.html#id1512">Metafunction</a></h1>
  16 <div class="section" id="id822">
  17 <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
  18 <p id="nullary-metafunction">A <em>metafunction</em> is a class or a class template that represents a
  19 function invocable at compile-time. An non-nullary metafunction is
  20 invoked by instantiating the class template with particular
  21 template parameters (metafunction arguments); the result of the
  22 metafunction application is accessible through the instantiation's
  23 nested <tt class="literal"><span class="pre">type</span></tt> typedef. All metafunction's arguments must be types
  24 (i.e. only <em>type template parameters</em> are allowed). A metafunction
  25 can have a variable number of parameters. A <em>nullary metafunction</em> is
  26 represented as a (template) class with a nested <tt class="literal"><span class="pre">type</span></tt> typename
  27 member.</p>
  28 </div>
  29 <div class="section" id="id823">
  30 <h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3>
  31 <p>In the following table and subsequent specifications, <tt class="literal"><span class="pre">f</span></tt> is a <a class="reference internal" href="./metafunction.html">Metafunction</a>.</p>
  32 <table border="1" class="docutils table">
  33 <colgroup>
  34 <col width="38%" />
  35 <col width="28%" />
  36 <col width="33%" />
  37 </colgroup>
  38 <thead valign="bottom">
  39 <tr><th class="head">Expression</th>
  40 <th class="head">Type</th>
  41 <th class="head">Complexity</th>
  42 </tr>
  43 </thead>
  44 <tbody valign="top">
  45 <tr><td><tt class="literal"><span class="pre">f::type</span></tt></td>
  46 <td>Any type</td>
  47 <td>Unspecified.</td>
  48 </tr>
  49 <tr><td><tt class="literal"><span class="pre">f&lt;&gt;::type</span></tt></td>
  50 <td>Any type</td>
  51 <td>Unspecified.</td>
  52 </tr>
  53 <tr><td><tt class="literal"><span class="pre">f&lt;a1,..,an&gt;::type</span></tt></td>
  54 <td>Any type</td>
  55 <td>Unspecified.</td>
  56 </tr>
  57 </tbody>
  58 </table>
  59 </div>
  60 <div class="section" id="id824">
  61 <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
  62 <pre class="literal-block">
  63 typedef f::type x;
  64 </pre>
  65 <table class="docutils field-list" frame="void" rules="none">
  66 <col class="field-name" />
  67 <col class="field-body" />
  68 <tbody valign="top">
  69 <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is a nullary <a class="reference internal" href="./metafunction.html">Metafunction</a>; <tt class="literal"><span class="pre">f::type</span></tt> is a <em>type-name</em>.</td>
  70 </tr>
  71 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction invocation.</td>
  72 </tr>
  73 </tbody>
  74 </table>
  75 <!-- ................................................................................... -->
  76 <pre class="literal-block">
  77 typedef f&lt;&gt;::type x;
  78 </pre>
  79 <table class="docutils field-list" frame="void" rules="none">
  80 <col class="field-name" />
  81 <col class="field-body" />
  82 <tbody valign="top">
  83 <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is a nullary <a class="reference internal" href="./metafunction.html">Metafunction</a>; <tt class="literal"><span class="pre">f&lt;&gt;::type</span></tt> is a <em>type-name</em>.</td>
  84 </tr>
  85 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction invocation.</td>
  86 </tr>
  87 </tbody>
  88 </table>
  89 <!-- ................................................................................... -->
  90 <pre class="literal-block">
  91 typedef f&lt;a1,<em>...</em> a<em>n</em>&gt;::type x;
  92 </pre>
  93 <table class="docutils field-list" frame="void" rules="none">
  94 <col class="field-name" />
  95 <col class="field-body" />
  96 <tbody valign="top">
  97 <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">f</span></tt> is an <em>n</em>-ary <a class="reference internal" href="./metafunction.html">Metafunction</a>; <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt> are types;
  98 <tt class="literal"><span class="pre">f&lt;a1,...an&gt;::type</span></tt> is a <em>type-name</em>.</td>
  99 </tr>
 100 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is the result of the metafunction invocation
 101 with the actual arguments <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>.</td>
 102 </tr>
 103 </tbody>
 104 </table>
 105 </div>
 106 <div class="section" id="id825">
 107 <h3><a class="subsection-title" href="#models" name="models">Models</a></h3>
 108 <ul class="simple">
 109 <li><a class="reference internal" href="./identity.html">identity</a></li>
 110 <li><a class="reference internal" href="./plus.html">plus</a></li>
 111 <li><a class="reference internal" href="./begin.html">begin</a></li>
 112 <li><a class="reference internal" href="./insert.html">insert</a></li>
 113 <li><a class="reference internal" href="./fold.html">fold</a></li>
 114 </ul>
 115 </div>
 116 <div class="section" id="id826">
 117 <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
 118 <p><a class="reference internal" href="./metafunctions.html">Metafunctions</a>, <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>, <a class="reference internal" href="./lambda-expression.html">Lambda Expression</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="./bind.html">bind</a></p>
 119 <!-- Metafunctions/Concepts//Metafunction Class |20 -->
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 126 Distributed under the Boost Software License, Version 1.0. (See accompanying
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