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: protect</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="./arg.html" class="navigation-link">Prev</a> <a href="./arithmetic-operations.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./arg.html" class="navigation-link">Back</a> Along</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="./protect.html" class="navigation-link">protect</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="protect"> 15<h1><a class="toc-backref" href="./composition-and-argument-binding.html#id1534">protect</a></h1> 16<div class="section" id="id953"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19template< 20 typename F 21 > 22struct <a href="./protect.html" class="identifier">protect</a> 23{ 24 // <em>unspecified</em> 25 // <em>...</em> 26}; 27</pre> 28</div> 29<div class="section" id="id954"> 30<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 31<p><tt class="literal"><span class="pre"><a href="./protect.html" class="identifier">protect</a></span></tt> is an identity wrapper for a <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a> that prevents 32its argument from being recognized as a <a class="reference internal" href="./terminology.html#bind-expression">bind expression</a>.</p> 33</div> 34<div class="section" id="id955"> 35<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 36<pre class="literal-block"> 37#include <<a href="../../../../boost/mpl/protect.hpp" class="header">boost/mpl/protect.hpp</a>> 38</pre> 39</div> 40<div class="section" id="id956"> 41<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> 42<table border="1" class="docutils table"> 43<colgroup> 44<col width="19%" /> 45<col width="33%" /> 46<col width="48%" /> 47</colgroup> 48<thead valign="bottom"> 49<tr><th class="head">Parameter</th> 50<th class="head">Requirement</th> 51<th class="head">Description</th> 52</tr> 53</thead> 54<tbody valign="top"> 55<tr><td><tt class="literal"><span class="pre">F</span></tt></td> 56<td><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a></td> 57<td>A metafunction class to wrap.</td> 58</tr> 59</tbody> 60</table> 61</div> 62<div class="section" id="id957"> 63<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 64<p>For any <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a> <tt class="literal"><span class="pre">f</span></tt>:</p> 65<pre class="literal-block"> 66typedef <a href="./protect.html" class="identifier">protect</a><f> g; 67</pre> 68<table class="docutils field-list" frame="void" rules="none"> 69<col class="field-name" /> 70<col class="field-body" /> 71<tbody valign="top"> 72<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> 73</td> 74</tr> 75<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">If <tt class="literal"><span class="pre">f</span></tt> is a <a class="reference internal" href="./terminology.html#bind-expression">bind expression</a>, equivalent to</p> 76<pre class="literal-block"> 77struct g 78{ 79 template< 80 typename U1 = <em>unspecified</em>,<em>...</em> typename U<em>n</em> = <em>unspecified</em> 81 > 82 struct <a href="./apply.html" class="identifier">apply</a> 83 : <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em><f,U1,<em>...</em>U<em>n</em>> 84 { 85 }; 86}; 87</pre> 88<p class="last">otherwise equivalent to <tt class="literal"><span class="pre">typedef</span> <span class="pre">f</span> <span class="pre">g;</span></tt>.</p> 89</td> 90</tr> 91</tbody> 92</table> 93</div> 94<div class="section" id="id958"> 95<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 96<pre class="literal-block"> 97struct f 98{ 99 template< typename T1, typename T2 > struct <a href="./apply.html" class="identifier">apply</a> 100 { 101 typedef T2 type; 102 }; 103}; 104 105typedef <a href="./bind.html" class="identifier">bind</a>< <a href="./quote.html" class="identifier">quote</a><tt class="literal"><span class="pre">3</span></tt><<a href="./if.html" class="identifier">if_</a>>,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>,<a href="./bind.html" class="identifier">bind</a><f,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>> > b1; 106typedef <a href="./bind.html" class="identifier">bind</a>< <a href="./quote.html" class="identifier">quote</a><tt class="literal"><span class="pre">3</span></tt><<a href="./if.html" class="identifier">if_</a>>,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>,<a href="./protect.html" class="identifier">protect</a>< <a href="./bind.html" class="identifier">bind</a><f,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>> > > b2; 107 108typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">2</span></tt>< b1,<a href="./bool.html" class="identifier">false_</a>,char >::type r1; 109typedef <a href="./apply-wrap.html" class="identifier">apply_wrap</a><tt class="literal"><span class="pre">2</span></tt>< b2,<a href="./bool.html" class="identifier">false_</a>,char >::type r2; 110 111<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same<r1,char> )); 112<a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same<r2,<a href="./protect.html" class="identifier">protect</a>< <a href="./bind.html" class="identifier">bind</a><f,<a href="./placeholders.html" class="identifier">_1</a>,<a href="./placeholders.html" class="identifier">_2</a>> > > )); 113</pre> 114</div> 115<div class="section" id="id959"> 116<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 117<p><a class="reference internal" href="./composition-and-argument-binding.html">Composition and Argument Binding</a>, <a class="reference internal" href="./invocation.html">invocation</a>, <a class="reference internal" href="./bind.html">bind</a>, <a class="reference internal" href="./quote.html">quote</a>, <a class="reference internal" href="./apply-wrap.html">apply_wrap</a></p> 118</div> 119</div> 120 121<div class="footer-separator"></div> 122<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./arg.html" class="navigation-link">Prev</a> <a href="./arithmetic-operations.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./arg.html" class="navigation-link">Back</a> Along</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> 123<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 124Distributed under the Boost Software License, Version 1.0. (See accompanying 125file 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> 126</html> 127