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<div><h2 class="title">
<a name="ref"></a>Chapter&#160;17.&#160;Boost.Ref</h2></div>
<div><div class="author"><h3 class="author">
<span class="firstname">Jaakko</span> <span class="surname">J&#228;rvi</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 &#169; 1999, 2000 Jaakko J&#228;rvi</p></div>
<div><p class="copyright">Copyright &#169; 2001, 2002 Peter Dimov</p></div>
<div><p class="copyright">Copyright &#169; 2002 David Abrahams</p></div>
<div><div class="legalnotice">
<a name="id2522575"></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 &lt;boost/ref.hpp&gt;</a></span></dt></dl></dd>
<dt><span class="section"><a href="ref/ack.html">Acknowledgements</a></span></dt>
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<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&lt;T&gt;</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&lt;T&gt;</code>, 
  a function <code class="computeroutput">boost::unwrap_ref</code>
  that unwraps a <code class="computeroutput">boost::reference_wrapper&lt;T&gt;</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&lt;T&gt;</a></code>
  and
  <code class="computeroutput"><a class="link" href="boost/unwrap_reference.html" title="Class template unwrap_reference">boost::unwrap_reference&lt;T&gt;</a></code>.</p>
<p>The purpose of
  <code class="computeroutput">boost::reference_wrapper&lt;T&gt;</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&lt;T&gt;</code> provides an implicit
  conversion to <code class="computeroutput">T&amp;</code>. This usually allows the function
  templates to work on references unmodified.</p>
<p><code class="computeroutput">boost::reference_wrapper&lt;T&gt;</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&lt;X&gt;(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&lt;X const&gt;(x)</code>.</p>
<p>The expression <code class="computeroutput">boost::unwrap_ref(x)</code>
  returns a
  <code class="computeroutput">boost::unwrap_reference&lt;X&gt;::type&amp;</code> where X
  is the type of x.</p>
<p>The expression
  <code class="computeroutput">boost::is_reference_wrapper&lt;T&gt;::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&lt;T&gt;::type</code> is T::type if T
  is a <code class="computeroutput">reference_wrapper</code>, T otherwise.</p>
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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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