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<title>Chapter 23. Boost.Ref</title>
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<div><h2 class="title">
<a name="ref"></a>Chapter 23. 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="id3190801"></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>.
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<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>
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<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>
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<td align="left"><p><small>Last revised: June 03, 2009 at 15:36:08 +0100</small></p></td>
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