boost_mpl/doc/refmanual/always.html

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<!-- Copyright Aleksey Gurtovoy 2006. Distributed under the Boost -->
<!-- Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="generator" content="Docutils 0.3.6: http://docutils.sourceforge.net/" />
<title>The MPL Reference Manual: always</title>
<link rel="stylesheet" href="../style.css" type="text/css" />
</head>
<body class="docframe refmanual">
<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./identity.html" class="navigation-link">Prev</a>&nbsp;<a href="./inherit.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./identity.html" class="navigation-link">Back</a>&nbsp;<a href="./inherit.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./miscellaneous.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>
<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="./miscellaneous.html" class="navigation-link">Miscellaneous</a> / <a href="./always.html" class="navigation-link">always</a></td>
</tr></table><div class="header-separator"></div>
<div class="section" id="always">
<h1><a class="toc-backref" href="./miscellaneous.html#id489" name="always">always</a></h1>
<div class="section" id="always-synopsis">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
template&lt; 
      typename X
    &gt;
struct <a href="./always.html" class="identifier">always</a>
{
    // <em>unspecified</em>
    // <em>...</em>
};
</pre>
</div>
<div class="section" id="always-description">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p><tt class="literal"><span class="pre"><a href="./always.html" class="identifier">always</a>&lt;X&gt;</span></tt> specialization is a variadic <a class="reference" href="./metafunction-class.html">Metafunction Class</a> always returning the 
same type, <tt class="literal"><span class="pre">X</span></tt>, regardless of the number and types of passed arguments.</p>
</div>
<div class="section" id="always-header">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/always.hpp" class="header">boost/mpl/always.hpp</a>&gt;
</pre>
</div>
<div class="section" id="always-model-of">
<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3>
<p><a class="reference" href="./metafunction-class.html">Metafunction Class</a></p>
</div>
<div class="section" id="always-parameters">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
<table border="1" class="table">
<colgroup>
<col width="22%" />
<col width="28%" />
<col width="51%" />
</colgroup>
<thead valign="bottom">
<tr><th>Parameter</th>
<th>Requirement</th>
<th>Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="literal"><span class="pre">X</span></tt></td>
<td>Any type</td>
<td>A type to be returned.</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="always-expression-semantics">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For an arbitrary type <tt class="literal"><span class="pre">x</span></tt>:</p>
<pre class="literal-block">
typedef <a href="./always.html" class="identifier">always</a>&lt;x&gt; f;
</pre>
<table class="field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference" href="./metafunction-class.html">Metafunction Class</a>.</td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p>
<pre class="last literal-block">
struct f : <a href="./bind.html" class="identifier">bind</a>&lt; <a href="./identity.html" class="identifier">identity</a>&lt;_1&gt;, x > {};
</pre>
</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="always-example">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
typedef <a href="./always.html" class="identifier">always</a>&lt;true_&gt; always_true;

<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./apply.html" class="identifier">apply</a>&lt; always_true,false_&gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./apply.html" class="identifier">apply</a>&lt; always_true,false_,false_ &gt; ));
<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./apply.html" class="identifier">apply</a>&lt; always_true,false_,false_,false_ > ));
</pre>
</div>
<div class="section" id="always-see-also">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference" href="./metafunctions.html">Metafunctions</a>, <a class="reference" href="./metafunction-class.html">Metafunction Class</a>, <a class="refentry reference" href="./identity.html"><tt class="refentry literal"><span class="pre">identity</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="./apply.html"><tt class="refentry literal"><span class="pre">apply</span></tt></a></p>
<!-- modtime: November 13, 2004 02:52:37 +0000 -->
<!-- Metafunctions/Miscellaneous//inherit |30 -->
</div>
</div>

<div class="footer-separator"></div>
<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./identity.html" class="navigation-link">Prev</a>&nbsp;<a href="./inherit.html" class="navigation-link">Next</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./identity.html" class="navigation-link">Back</a>&nbsp;<a href="./inherit.html" class="navigation-link">Along</a></span><span class="navigation-group-separator">&nbsp;|&nbsp;</span><span class="navigation-group"><a href="./miscellaneous.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>
</tr></table></body>
</html>