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: always</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="./identity.html" class="navigation-link">Prev</a> <a href="./inherit.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./identity.html" class="navigation-link">Back</a> <a href="./inherit.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./miscellaneous.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="./miscellaneous.html" class="navigation-link">Miscellaneous</a> / <a href="./always.html" class="navigation-link">always</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="always"> 15<h1><a class="toc-backref" href="./miscellaneous.html#id1565">always</a></h1> 16<div class="section" id="id1155"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19template< 20 typename X 21 > 22struct <a href="./always.html" class="identifier">always</a> 23{ 24 // <em>unspecified</em> 25 // <em>...</em> 26}; 27</pre> 28</div> 29<div class="section" id="id1156"> 30<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 31<p><tt class="literal"><span class="pre"><a href="./always.html" class="identifier">always</a><X></span></tt> specialization is a variadic <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a> always returning the 32same type, <tt class="literal"><span class="pre">X</span></tt>, regardless of the number and types of passed arguments.</p> 33</div> 34<div class="section" id="id1157"> 35<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 36<pre class="literal-block"> 37#include <<a href="../../../../boost/mpl/always.hpp" class="header">boost/mpl/always.hpp</a>> 38</pre> 39</div> 40<div class="section" id="id1158"> 41<h3><a class="subsection-title" href="#model-of" name="model-of">Model of</a></h3> 42<p><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a></p> 43</div> 44<div class="section" id="id1159"> 45<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> 46<table border="1" class="docutils table"> 47<colgroup> 48<col width="22%" /> 49<col width="28%" /> 50<col width="51%" /> 51</colgroup> 52<thead valign="bottom"> 53<tr><th class="head">Parameter</th> 54<th class="head">Requirement</th> 55<th class="head">Description</th> 56</tr> 57</thead> 58<tbody valign="top"> 59<tr><td><tt class="literal"><span class="pre">X</span></tt></td> 60<td>Any type</td> 61<td>A type to be returned.</td> 62</tr> 63</tbody> 64</table> 65</div> 66<div class="section" id="id1160"> 67<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 68<p>For an arbitrary type <tt class="literal"><span class="pre">x</span></tt>:</p> 69<pre class="literal-block"> 70typedef <a href="./always.html" class="identifier">always</a><x> f; 71</pre> 72<table class="docutils field-list" frame="void" rules="none"> 73<col class="field-name" /> 74<col class="field-body" /> 75<tbody valign="top"> 76<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>.</p> 77</td> 78</tr> 79<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Equivalent to</p> 80<pre class="last literal-block"> 81struct f : <a href="./bind.html" class="identifier">bind</a>< <a href="./identity.html" class="identifier">identity</a><<a href="./placeholders.html" class="identifier">_1</a>>, x > {}; 82</pre> 83</td> 84</tr> 85</tbody> 86</table> 87</div> 88<div class="section" id="id1161"> 89<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 90<pre class="literal-block"> 91typedef <a href="./always.html" class="identifier">always</a><<a href="./bool.html" class="identifier">true_</a>> always_true; 92 93<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./apply.html" class="identifier">apply</a>< always_true,<a href="./bool.html" class="identifier">false_</a>> )); 94<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./apply.html" class="identifier">apply</a>< always_true,<a href="./bool.html" class="identifier">false_</a>,<a href="./bool.html" class="identifier">false_</a> > )); 95<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( <a href="./apply.html" class="identifier">apply</a>< always_true,<a href="./bool.html" class="identifier">false_</a>,<a href="./bool.html" class="identifier">false_</a>,<a href="./bool.html" class="identifier">false_</a> > )); 96</pre> 97</div> 98<div class="section" id="id1162"> 99<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 100<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="./identity.html">identity</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./apply.html">apply</a></p> 101<!-- Metafunctions/Miscellaneous//inherit |30 --> 102</div> 103</div> 104 105<div class="footer-separator"></div> 106<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> <a href="./inherit.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./identity.html" class="navigation-link">Back</a> <a href="./inherit.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./miscellaneous.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> 107<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 108Distributed under the Boost Software License, Version 1.0. (See accompanying 109file 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> 110</html> 111