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: arg</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="./quote.html" class="navigation-link">Prev</a> <a href="./protect.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./quote.html" class="navigation-link">Back</a> <a href="./protect.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./composition-and-argument-binding.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="./composition-and-argument-binding.html" class="navigation-link">Composition and Argument Binding</a> / <a href="./arg.html" class="navigation-link">arg</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="arg"> 15<h1><a class="toc-backref" href="./composition-and-argument-binding.html#id1533">arg</a></h1> 16<div class="section" id="id946"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19template< int n > struct <a href="./arg.html" class="identifier">arg</a>; 20 21template<> struct <a href="./arg.html" class="identifier">arg</a><1> 22{ 23 template< typename A1,<em>...</em> typename A<em>n</em> = <em>unspecified</em> > 24 struct <a href="./apply.html" class="identifier">apply</a> 25 { 26 typedef A1 type; 27 }; 28}; 29 30<em>...</em> 31 32template<> struct <a href="./arg.html" class="identifier">arg</a><<em>n</em>> 33{ 34 template< typename A1,<em>...</em> typename A<em>n</em> > 35 struct <a href="./apply.html" class="identifier">apply</a> 36 { 37 typedef A<em>n</em> type; 38 }; 39}; 40</pre> 41</div> 42<div class="section" id="id947"> 43<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 44<p><tt class="literal"><span class="pre"><a href="./arg.html" class="identifier">arg</a><n></span></tt> specialization is a <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a> that return the <tt class="literal"><span class="pre">n</span></tt>th of its arguments.</p> 45</div> 46<div class="section" id="id948"> 47<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 48<pre class="literal-block"> 49#include <<a href="../../../../boost/mpl/arg.hpp" class="header">boost/mpl/arg.hpp</a>> 50</pre> 51</div> 52<div class="section" id="id949"> 53<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> 54<table border="1" class="docutils table"> 55<colgroup> 56<col width="15%" /> 57<col width="36%" /> 58<col width="48%" /> 59</colgroup> 60<thead valign="bottom"> 61<tr><th class="head">Parameter</th> 62<th class="head">Requirement</th> 63<th class="head">Description</th> 64</tr> 65</thead> 66<tbody valign="top"> 67<tr><td><tt class="literal"><span class="pre">n</span></tt></td> 68<td>An integral constant</td> 69<td>A number of argument to return.</td> 70</tr> 71</tbody> 72</table> 73</div> 74<div class="section" id="id950"> 75<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 76<p>For any integral constant <tt class="literal"><span class="pre">n</span></tt> in the range [1, <a class="reference internal" href="./limit-metafunction-arity.html">BOOST_MPL_LIMIT_METAFUNCTION_ARITY</a>] and 77arbitrary types <tt class="literal"><span class="pre">a1</span></tt>,... <tt class="literal"><span class="pre">an</span></tt>:</p> 78<pre class="literal-block"> 79typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em>< <a href="./arg.html" class="identifier">arg</a><<em>n</em>>,a1,<em>...</em>a<em>n</em> >::type x; 80</pre> 81<table class="docutils field-list" frame="void" rules="none"> 82<col class="field-name" /> 83<col class="field-body" /> 84<tbody valign="top"> 85<tr class="field"><th class="field-name">Return type:</th><td class="field-body">A type.</td> 86</tr> 87<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">x</span></tt> is identical to <tt class="literal"><span class="pre">an</span></tt>.</td> 88</tr> 89</tbody> 90</table> 91</div> 92<div class="section" id="id951"> 93<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 94<pre class="literal-block"> 95typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">5</span></tt>< <a href="./arg.html" class="identifier">arg</a><1>,bool,char,short,int,long >::type t1; 96typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">5</span></tt>< <a href="./arg.html" class="identifier">arg</a><3>,bool,char,short,int,long >::type t3; 97 98<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< t1, bool > )); 99<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same< t3, short > )); 100</pre> 101</div> 102<div class="section" id="id952"> 103<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 104<p><a class="reference internal" href="./composition-and-argument-binding.html">Composition and Argument Binding</a>, <a class="reference internal" href="./placeholders.html">Placeholders</a>, <a class="reference internal" href="./lambda.html">lambda</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./apply.html">apply</a>, <a class="reference internal" href="./apply-wrap.html">apply_wrap</a></p> 105<!-- Metafunctions/Composition and Argument Binding//protect |60 --> 106</div> 107</div> 108 109<div class="footer-separator"></div> 110<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./quote.html" class="navigation-link">Prev</a> <a href="./protect.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./quote.html" class="navigation-link">Back</a> <a href="./protect.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./composition-and-argument-binding.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> 111<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 112Distributed under the Boost Software License, Version 1.0. (See accompanying 113file 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> 114</html> 115