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7<title>The MPL Reference Manual: Metafunction Class</title>
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11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./metafunction.html" class="navigation-link">Prev</a>&nbsp;<a href="./lambda-expression.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./metafunction.html" class="navigation-link">Back</a>&nbsp;<a href="./lambda-expression.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-class.html" class="navigation-link">Metafunction Class</a></td>
13</tr></table><div class="header-separator"></div>
14<div class="section" id="metafunction-class">
15<h1><a class="toc-backref" href="./metafunctions-concepts.html#id439" name="metafunction-class">Metafunction Class</a></h1>
16<div class="section" id="summary">
17<h3><a class="subsection-title" href="#summary" name="summary">Summary</a></h3>
18<p>A <em>metafunction class</em> is a certain form of metafunction representation
19that enables higher-order metaprogramming. More precisely, it's a class
20with a publicly-accessible nested <a class="reference" href="./metafunction.html">Metafunction</a> called <tt class="literal"><span class="pre"><a href="./apply.html" class="identifier">apply</a></span></tt>.
21Correspondingly, a metafunction class invocation is defined as invocation
22of its nested <tt class="literal"><span class="pre"><a href="./apply.html" class="identifier">apply</a></span></tt> metafunction.</p>
23</div>
24<div class="section" id="metafunctions-metafunction-expression-requirements">
25<h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3>
26<p>In the following table and subsequent specifications, <tt class="literal"><span class="pre">f</span></tt> is a <a class="reference" href="./metafunction-class.html">Metafunction Class</a>.</p>
27<table border="1" class="table">
28<colgroup>
29<col width="36%" />
30<col width="32%" />
31<col width="32%" />
32</colgroup>
33<thead valign="bottom">
34<tr><th>Expression</th>
35<th>Type</th>
36<th>Complexity</th>
37</tr>
38</thead>
39<tbody valign="top">
40<tr><td><tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a>::type</span></tt></td>
41<td>Any type</td>
42<td>Unspecified.</td>
43</tr>
44<tr><td><tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a>&lt;&gt;::type</span></tt></td>
45<td>Any type</td>
46<td>Unspecified.</td>
47</tr>
48<tr><td><tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a>&lt;a1,...an&gt;::type</span></tt></td>
49<td>Any type</td>
50<td>Unspecified.</td>
51</tr>
52</tbody>
53</table>
54</div>
55<div class="section" id="metafunctions-metafunction-expression-semantics">
56<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
57<pre class="literal-block">
58typedef f::<a href="./apply.html" class="identifier">apply</a>::type x;
59</pre>
60<table class="field-list" frame="void" rules="none">
61<col class="field-name" />
62<col class="field-body" />
63<tbody valign="top">
64<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" href="./metafunction-class.html">Metafunction Class</a>; <tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a>::type</span></tt> is a <em>type-name</em>.</td>
65</tr>
66<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 class invocation.</td>
67</tr>
68</tbody>
69</table>
70<!-- ................................................................................... -->
71<pre class="literal-block">
72typedef f::<a href="./apply.html" class="identifier">apply</a>&lt;&gt;::type x;
73</pre>
74<table class="field-list" frame="void" rules="none">
75<col class="field-name" />
76<col class="field-body" />
77<tbody valign="top">
78<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" href="./metafunction-class.html">Metafunction Class</a>; <tt class="literal"><span class="pre">f::<a href="./apply.html" class="identifier">apply</a>&lt;&gt;::type</span></tt> is a <em>type-name</em>.</td>
79</tr>
80<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 class invocation.</td>
81</tr>
82</tbody>
83</table>
84<!-- ................................................................................... -->
85<pre class="literal-block">
86typedef f::<a href="./apply.html" class="identifier">apply</a>&lt;a1,<em>...</em>a<em>n</em>&gt;::type x;
87</pre>
88<table class="field-list" frame="void" rules="none">
89<col class="field-name" />
90<col class="field-body" />
91<tbody valign="top">
92<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 metafunction class; <tt class="literal"><span class="pre"><a href="./apply.html" class="identifier">apply</a></span></tt> is a <a class="reference" href="./metafunction.html">Metafunction</a>.</td>
93</tr>
94<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 class
95invocation with the actual arguments <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>.</td>
96</tr>
97</tbody>
98</table>
99</div>
100<div class="section" id="metafunctions-metafunction-models">
101<h3><a class="subsection-title" href="#models" name="models">Models</a></h3>
102<ul class="simple">
103<li><a class="refentry reference" href="./always.html"><tt class="refentry literal"><span class="pre">always</span></tt></a></li>
104<li><a class="refentry reference" href="./arg.html"><tt class="refentry literal"><span class="pre">arg</span></tt></a></li>
105<li><a class="refentry reference" href="./quote.html"><tt class="refentry literal"><span class="pre">quote</span></tt></a></li>
106<li><a class="refentry reference" href="./numeric-cast.html"><tt class="refentry literal"><span class="pre">numeric_cast</span></tt></a></li>
107<li><a class="refentry reference" href="./unpack-args.html"><tt class="refentry literal"><span class="pre">unpack_args</span></tt></a></li>
108</ul>
109</div>
110<div class="section" id="metafunctions-metafunction-see-also">
111<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
112<p><a class="reference" href="./metafunctions.html">Metafunctions</a>, <a class="reference" href="./metafunction.html">Metafunction</a>, <a class="reference" href="./lambda-expression.html">Lambda Expression</a>, <a class="reference" href="./invocation.html">invocation</a>, <a class="refentry reference" href="./apply-wrap.html"><tt class="refentry literal"><span class="pre">apply_wrap</span></tt></a>, <a class="refentry reference" href="./bind.html"><tt class="refentry literal"><span class="pre">bind</span></tt></a>, <a class="refentry reference" href="./quote.html"><tt class="refentry literal"><span class="pre">quote</span></tt></a></p>
113<!-- modtime: November 10, 2004 04:37:44 +0000 -->
114<!-- Metafunctions/Concepts//Lambda Expression |30 -->
115</div>
116</div>
117
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