1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>ref</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Chapter 1. Boost.Core"> 8<link rel="up" href="../index.html" title="Chapter 1. Boost.Core"> 9<link rel="prev" href="quick_exit.html" title="quick_exit"> 10<link rel="next" href="../boost/is_reference_wrapper.html" title="Struct template is_reference_wrapper"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="quick_exit.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="../boost/is_reference_wrapper.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="core.ref"></a><a class="link" href="ref.html" title="ref">ref</a> 28</h2></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="ref.html#core.ref.introduction">Introduction</a></span></dt> 31<dt><span class="section"><a href="ref.html#core.reference">Reference</a></span></dt> 32<dt><span class="section"><a href="ref.html#core.ref.acknowledgments">Acknowledgments</a></span></dt> 33</dl></div> 34<div class="simplesect"> 35<div class="titlepage"><div><div><h3 class="title"> 36<a name="idm45312826658832"></a>Authors</h3></div></div></div> 37<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 38<li class="listitem"> 39 Jaakko Järvi 40 </li> 41<li class="listitem"> 42 Peter Dimov 43 </li> 44<li class="listitem"> 45 Douglas Gregor 46 </li> 47<li class="listitem"> 48 Dave Abrahams 49 </li> 50<li class="listitem"> 51 Frank Mori Hess 52 </li> 53<li class="listitem"> 54 Ronald Garcia 55 </li> 56</ul></div> 57</div> 58<div class="section"> 59<div class="titlepage"><div><div><h3 class="title"> 60<a name="core.ref.introduction"></a><a class="link" href="ref.html#core.ref.introduction" title="Introduction">Introduction</a> 61</h3></div></div></div> 62<p> 63 The Ref library is a small library that is useful for passing references 64 to function templates (algorithms) that would usually take copies of their 65 arguments. It defines the class template <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>, 66 two functions <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">ref</span></code> and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cref</span></code> 67 that return instances of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>, 68 a function <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unwrap_ref</span></code> that unwraps a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or 69 returns a reference to any other type of object, and the two traits classes 70 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> and 71 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unwrap_reference</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>. 72 </p> 73<p> 74 The purpose of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is 75 to contain a reference to an object of type <code class="computeroutput"><span class="identifier">T</span></code>. 76 It is primarily used to "feed" references to function templates 77 (algorithms) that take their parameter by value. 78 </p> 79<p> 80 To support this usage, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> 81 provides an implicit conversion to <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>. This usually allows the function templates 82 to work on references unmodified. 83 </p> 84<p> 85 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is 86 both CopyConstructible and Assignable (ordinary references are not Assignable). 87 </p> 88<p> 89 The <code class="computeroutput"><span class="identifier">expression</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> returns 90 a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">X</span><span class="special">>(</span><span class="identifier">x</span><span class="special">)</span></code> where 91 <code class="computeroutput"><span class="identifier">X</span></code> is the type of <code class="computeroutput"><span class="identifier">x</span></code>. Similarly, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">cref</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> 92 returns a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">X</span> <span class="keyword">const</span><span class="special">>(</span><span class="identifier">x</span><span class="special">)</span></code>. 93 </p> 94<p> 95 The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unwrap_ref</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> returns 96 a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unwrap_reference</span><span class="special"><</span><span class="identifier">X</span><span class="special">>::</span><span class="identifier">type</span><span class="special">&</span></code> 97 where <code class="computeroutput"><span class="identifier">X</span></code> is the type of <code class="computeroutput"><span class="identifier">x</span></code>. 98 </p> 99<p> 100 The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> is <code class="computeroutput"><span class="keyword">true</span></code> 101 if <code class="computeroutput"><span class="identifier">T</span></code> is a <code class="computeroutput"><span class="identifier">reference_wrapper</span></code>, 102 and <code class="computeroutput"><span class="keyword">false</span></code> otherwise. 103 </p> 104<p> 105 The type-expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unwrap_reference</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span></code> is <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">type</span></code> 106 if <code class="computeroutput"><span class="identifier">T</span></code> is a <code class="computeroutput"><span class="identifier">reference_wrapper</span></code>, 107 <code class="computeroutput"><span class="identifier">T</span></code> otherwise. 108 </p> 109</div> 110<div class="section"> 111<div class="titlepage"><div><div><h3 class="title"> 112<a name="core.reference"></a>Reference</h3></div></div></div> 113<div class="section"> 114<div class="titlepage"><div><div><h4 class="title"> 115<a name="header.boost.core.ref_hpp"></a>Header <<a href="../../../../../boost/core/ref.hpp" target="_top">boost/core/ref.hpp</a>></h4></div></div></div> 116<pre class="synopsis"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 117 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="keyword">struct</span> <a class="link" href="../boost/is_reference_wrapper.html" title="Struct template is_reference_wrapper">is_reference_wrapper</a><span class="special">;</span> 118 119 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="keyword">class</span> <a class="link" href="../boost/reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special">;</span> 120 121 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="keyword">struct</span> <a class="link" href="../boost/unwrap_reference.html" title="Struct template unwrap_reference">unwrap_reference</a><span class="special">;</span> 122 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <a class="link" href="../boost/reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special"><</span> <span class="identifier">T</span> <span class="special">></span> <span class="keyword">const</span> <a class="link" href="../boost/ref_idm45442566532320.html" title="Function template ref"><span class="identifier">ref</span></a><span class="special">(</span><span class="identifier">T</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 123 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <a class="link" href="../boost/reference_wrapper.html" title="Class template reference_wrapper">reference_wrapper</a><span class="special"><</span> <span class="identifier">T</span> <span class="keyword">const</span> <span class="special">></span> <span class="keyword">const</span> <a class="link" href="../boost/cref_idm45442566527344.html" title="Function template cref"><span class="identifier">cref</span></a><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 124 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="keyword">void</span> <a class="link" href="../boost/ref_idm45442555713568.html" title="Function template ref"><span class="identifier">ref</span></a><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&&</span><span class="special">)</span><span class="special">;</span> 125 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="keyword">void</span> <a class="link" href="../boost/cref_idm45442555710800.html" title="Function template cref"><span class="identifier">cref</span></a><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&&</span><span class="special">)</span><span class="special">;</span> 126 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <a class="link" href="../boost/unwrap_reference.html" title="Struct template unwrap_reference">unwrap_reference</a><span class="special"><</span> <span class="identifier">T</span> <span class="special">></span><span class="special">::</span><span class="identifier">type</span> <span class="special">&</span> <a class="link" href="../boost/unwrap_ref.html" title="Function template unwrap_ref"><span class="identifier">unwrap_ref</span></a><span class="special">(</span><span class="identifier">T</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 127<span class="special">}</span></pre> 128</div> 129</div> 130<div class="section"> 131<div class="titlepage"><div><div><h3 class="title"> 132<a name="core.ref.acknowledgments"></a><a class="link" href="ref.html#core.ref.acknowledgments" title="Acknowledgments">Acknowledgments</a> 133</h3></div></div></div> 134<p> 135 <code class="computeroutput"><span class="identifier">ref</span></code> and <code class="computeroutput"><span class="identifier">cref</span></code> 136 were originally part of the Tuple library by Jaakko Järvi. They were 137 "promoted to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span></code> 138 status" by Peter Dimov because they are generally useful. Douglas Gregor 139 and Dave Abrahams contributed <code class="computeroutput"><span class="identifier">is_reference_wrapper</span></code> 140 and <code class="computeroutput"><span class="identifier">unwrap_reference</span></code>. Frank 141 Mori Hess and Ronald Garcia contributed <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">unwrap_ref</span></code>. 142 </p> 143</div> 144</div> 145<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 146<td align="left"></td> 147<td align="right"><div class="copyright-footer">Copyright © 2014 Peter Dimov<br>Copyright © 2014 Glen Fernandes<br>Copyright © 2014 Andrey Semashev<p> 148 Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost 149 Software License, Version 1.0</a>. 150 </p> 151</div></td> 152</tr></table> 153<hr> 154<div class="spirit-nav"> 155<a accesskey="p" href="quick_exit.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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="../boost/is_reference_wrapper.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 156</div> 157</body> 158</html> 159
