[ceph.git] / ceph / src / boost / libs / mpl / doc / refmanual / metafunction.html

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<div class="section" id="metafunction">
<h1><a class="toc-backref" href="./metafunctions-concepts.html#id1512">Metafunction</a></h1>
<div class="section" id="id822">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p id="nullary-metafunction">A <em>metafunction</em> is a class or a class template that represents a
function invocable at compile-time. An non-nullary metafunction is
invoked by instantiating the class template with particular
template parameters (metafunction arguments); the result of the
metafunction application is accessible through the instantiation's
nested <tt class="literal"><span class="pre">type</span></tt> typedef. All metafunction's arguments must be types
(i.e. only <em>type template parameters</em> are allowed). A metafunction
can have a variable number of parameters. A <em>nullary metafunction</em> is
represented as a (template) class with a nested <tt class="literal"><span class="pre">type</span></tt> typename
member.</p>
</div>
<div class="section" id="id823">
<h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3>
<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>
<table border="1" class="docutils table">
<colgroup>
<col width="38%" />
<col width="28%" />
<col width="33%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Expression</th>
<th class="head">Type</th>
<th class="head">Complexity</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">f::type</span></tt></td>
<td>Any type</td>
<td>Unspecified.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">f&lt;&gt;::type</span></tt></td>
<td>Any type</td>
<td>Unspecified.</td>
</tr>
<tr><td><tt class="literal"><span class="pre">f&lt;a1,..,an&gt;::type</span></tt></td>
<td>Any type</td>
<td>Unspecified.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id824">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<pre class="literal-block">
typedef f::type x;
</pre>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<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>
</tr>
<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>
</tr>
</tbody>
</table>
<!-- ................................................................................... -->
<pre class="literal-block">
typedef f&lt;&gt;::type x;
</pre>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<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>
</tr>
<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>
</tr>
</tbody>
</table>
<!-- ................................................................................... -->
<pre class="literal-block">
typedef f&lt;a1,<em>...</em> a<em>n</em>&gt;::type x;
</pre>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<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;
<tt class="literal"><span class="pre">f&lt;a1,...an&gt;::type</span></tt> is a <em>type-name</em>.</td>
</tr>
<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
with the actual arguments <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="id825">
<h3><a class="subsection-title" href="#models" name="models">Models</a></h3>
<ul class="simple">
<li><a class="reference internal" href="./identity.html">identity</a></li>
<li><a class="reference internal" href="./plus.html">plus</a></li>
<li><a class="reference internal" href="./begin.html">begin</a></li>
<li><a class="reference internal" href="./insert.html">insert</a></li>
<li><a class="reference internal" href="./fold.html">fold</a></li>
</ul>
</div>
<div class="section" id="id826">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<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>
<!-- Metafunctions/Concepts//Metafunction Class |20 -->
</div>
</div>

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<td><div class="copyright-footer"><div class="copyright">Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams</div>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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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Commit	Line	Data
7c673cae FG	1	<?xml version="1.0" encoding="utf-8" ?>
	2	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	3	<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
	4	<head>
	5	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
	6	<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" />
	7	<title>The MPL Reference Manual: Metafunction</title>
	8	<link rel="stylesheet" href="../style.css" type="text/css" />
	9	</head>
	10	<body class="docframe refmanual">
	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> <a href="./metafunction-class.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> \| </span><span class="navigation-group">Back <a href="./metafunction-class.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> \| </span><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> \| </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>
	13	</tr></table><div class="header-separator"></div>
	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<>::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<a1,..,an>::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<>::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<>::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<a1,<em>...</em> a<em>n</em>>::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<a1,...an>::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 -->
120	</div>
121	</div>
122
123	<div class="footer-separator"></div>
124	<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Prev</a> <a href="./metafunction-class.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> \| </span><span class="navigation-group">Back <a href="./metafunction-class.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> \| </span><span class="navigation-group"><a href="./metafunctions-concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> \| </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
125	<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div>
126	Distributed under the Boost Software License, Version 1.0. (See accompanying
127	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>
128	</html>