<?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"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> <title>The MPL Reference Manual: protect</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="./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> <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> </tr></table><div class="header-separator"></div> <div class="section" id="protect"> <h1><a class="toc-backref" href="./composition-and-argument-binding.html#id1534">protect</a></h1> <div class="section" id="id953"> <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> <pre class="literal-block"> template< typename F > struct <a href="./protect.html" class="identifier">protect</a> { // <em>unspecified</em> // <em>...</em> }; </pre> </div> <div class="section" id="id954"> <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> <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 its argument from being recognized as a <a class="reference internal" href="./terminology.html#bind-expression">bind expression</a>.</p> </div> <div class="section" id="id955"> <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> <pre class="literal-block"> #include <<a href="../../../../boost/mpl/protect.hpp" class="header">boost/mpl/protect.hpp</a>> </pre> </div> <div class="section" id="id956"> <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> <table border="1" class="docutils table"> <colgroup> <col width="19%" /> <col width="33%" /> <col width="48%" /> </colgroup> <thead valign="bottom"> <tr><th class="head">Parameter</th> <th class="head">Requirement</th> <th class="head">Description</th> </tr> </thead> <tbody valign="top"> <tr><td><tt class="literal"><span class="pre">F</span></tt></td> <td><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a></td> <td>A metafunction class to wrap.</td> </tr> </tbody> </table> </div> <div class="section" id="id957"> <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> <p>For any <a class="reference internal" href="./metafunction-class.html">Metafunction Class</a> <tt class="literal"><span class="pre">f</span></tt>:</p> <pre class="literal-block"> typedef <a href="./protect.html" class="identifier">protect</a><f> g; </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">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./metafunction-class.html">Metafunction Class</a>.</p> </td> </tr> <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> <pre class="literal-block"> struct g { template< typename U1 = <em>unspecified</em>,<em>...</em> typename U<em>n</em> = <em>unspecified</em> > struct <a href="./apply.html" class="identifier">apply</a> : <a href="./apply-wrap.html" class="identifier">apply_wrap</a><em>n</em><f,U1,<em>...</em>U<em>n</em>> { }; }; </pre> <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> </td> </tr> </tbody> </table> </div> <div class="section" id="id958"> <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> <pre class="literal-block"> struct f { template< typename T1, typename T2 > struct <a href="./apply.html" class="identifier">apply</a> { typedef T2 type; }; }; typedef <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; typedef <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; typedef <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; typedef <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; <a href="./assert.html" class="identifier">BOOST_MPL_ASSERT</a>(( is_same<r1,char> )); <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>> > > )); </pre> </div> <div class="section" id="id959"> <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> <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> </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="./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> <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. 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