<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Chapter 17. Boost.Ref</title> <link rel="stylesheet" href="../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> <link rel="up" href="libraries.html" title="Part I. The Boost C++ Libraries (BoostBook Subset)"> <link rel="prev" href="boost_random/history_and_acknowledgements.html" title="History and Acknowledgements"> <link rel="next" href="ref/reference.html" title="Reference"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../boost.png"></td> <td align="center"><a href="../../index.html">Home</a></td> <td align="center"><a href="../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="boost_random/history_and_acknowledgements.html"><img src="../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="libraries.html"><img src="../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="ref/reference.html"><img src="../../doc/src/images/next.png" alt="Next"></a> </div> <div class="chapter"> <div class="titlepage"><div> <div><h2 class="title"> <a name="ref"></a>Chapter 17. Boost.Ref</h2></div> <div><div class="author"><h3 class="author"> <span class="firstname">Jaakko</span> <span class="surname">Järvi</span> </h3></div></div> <div><div class="author"><h3 class="author"> <span class="firstname">Peter</span> <span class="surname">Dimov</span> </h3></div></div> <div><div class="author"><h3 class="author"> <span class="firstname">Douglas</span> <span class="surname">Gregor</span> </h3></div></div> <div><div class="author"><h3 class="author"> <span class="firstname">Dave</span> <span class="surname">Abrahams</span> </h3></div></div> <div><p class="copyright">Copyright © 1999, 2000 Jaakko Järvi</p></div> <div><p class="copyright">Copyright © 2001, 2002 Peter Dimov</p></div> <div><p class="copyright">Copyright © 2002 David Abrahams</p></div> <div><div class="legalnotice"> <a name="id2532635"></a><p>Subject to the Boost Software License, Version 1.0. See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>. </p> </div></div> </div></div> <div class="toc"> <p><b>Table of Contents</b></p> <dl> <dt><span class="section"><a href="ref.html#ref.intro">Introduction</a></span></dt> <dt><span class="section"><a href="ref/reference.html">Reference</a></span></dt> <dd><dl><dt><span class="section"><a href="ref/reference.html#header.boost.ref_hpp">Header <boost/ref.hpp></a></span></dt></dl></dd> <dt><span class="section"><a href="ref/ack.html">Acknowledgements</a></span></dt> </dl> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="ref.intro"></a>Introduction</h2></div></div></div> <p>The Ref library is a small library that is useful for passing references to function templates (algorithms) that would usually take copies of their arguments. It defines the class template <code class="computeroutput"><a class="link" href="boost/reference_wrapper.html" title="Class template reference_wrapper">boost::reference_wrapper<T></a></code>, two functions <code class="computeroutput">boost::ref</code> and <code class="computeroutput">boost::cref</code> that return instances of <code class="computeroutput">boost::reference_wrapper<T></code>, a function <code class="computeroutput">boost::unwrap_ref</code> that unwraps a <code class="computeroutput">boost::reference_wrapper<T></code> or returns a reference to any other type of object, and the two traits classes <code class="computeroutput"><a class="link" href="boost/is_reference_wrapper.html" title="Class template is_reference_wrapper">boost::is_reference_wrapper<T></a></code> and <code class="computeroutput"><a class="link" href="boost/unwrap_reference.html" title="Class template unwrap_reference">boost::unwrap_reference<T></a></code>.</p> <p>The purpose of <code class="computeroutput">boost::reference_wrapper<T></code> is to contain a reference to an object of type T. It is primarily used to "feed" references to function templates (algorithms) that take their parameter by value.</p> <p>To support this usage, <code class="computeroutput">boost::reference_wrapper<T></code> provides an implicit conversion to <code class="computeroutput">T&</code>. This usually allows the function templates to work on references unmodified.</p> <p><code class="computeroutput">boost::reference_wrapper<T></code> is both CopyConstructible and Assignable (ordinary references are not Assignable).</p> <p>The expression <code class="computeroutput">boost::ref(x)</code> returns a <code class="computeroutput">boost::reference_wrapper<X>(x)</code> where X is the type of x. Similarly, <code class="computeroutput">boost::cref(x)</code> returns a <code class="computeroutput">boost::reference_wrapper<X const>(x)</code>.</p> <p>The expression <code class="computeroutput">boost::unwrap_ref(x)</code> returns a <code class="computeroutput">boost::unwrap_reference<X>::type&</code> where X is the type of x.</p> <p>The expression <code class="computeroutput">boost::is_reference_wrapper<T>::value</code> is true if T is a <code class="computeroutput">reference_wrapper</code>, and false otherwise.</p> <p>The type-expression <code class="computeroutput">boost::unwrap_reference<T>::type</code> is T::type if T is a <code class="computeroutput">reference_wrapper</code>, T otherwise.</p> </div> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"><p><small>Last revised: June 03, 2009 at 15:36:08 +0100</small></p></td> <td align="right"><div class="copyright-footer"></div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="boost_random/history_and_acknowledgements.html"><img src="../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="libraries.html"><img src="../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="ref/reference.html"><img src="../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>