1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>How the library works</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../move.html" title="Chapter 25. Boost.Move"> 10<link rel="prev" href="emulation_limitations.html" title="Emulation limitations"> 11<link rel="next" href="thanks_to.html" title="Thanks and credits"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="emulation_limitations.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../move.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="thanks_to.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="move.how_the_library_works"></a><a class="link" href="how_the_library_works.html" title="How the library works">How the library works</a> 29</h2></div></div></div> 30<p> 31 <span class="bold"><strong>Boost.Move</strong></span> is based on macros that are expanded 32 to true rvalue references in C++0x compilers and emulated rvalue reference 33 classes and conversion operators in C++03 compilers. 34 </p> 35<p> 36 In C++03 compilers <span class="bold"><strong>Boost.Move</strong></span> defines a class 37 named <code class="computeroutput"><span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span></code>: 38 </p> 39<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 40<span class="keyword">class</span> <span class="identifier">rv</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">T</span> 41<span class="special">{</span> 42 <span class="identifier">rv</span><span class="special">();</span> 43 <span class="special">~</span><span class="identifier">rv</span><span class="special">();</span> 44 <span class="identifier">rv</span><span class="special">(</span><span class="identifier">rv</span> <span class="keyword">const</span><span class="special">&);</span> 45 <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">rv</span> <span class="keyword">const</span><span class="special">&);</span> 46<span class="special">};</span> 47</pre> 48<p> 49 which is convertible to the movable base class (usual C++ derived to base conversion). 50 When users mark their classes as <code class="computeroutput"><a class="link" href="../BOOST_MOVABL_1_3_26_20_7_3.html" title="Macro BOOST_MOVABLE_BUT_NOT_COPYABLE">BOOST_MOVABLE_BUT_NOT_COPYABLE</a></code> 51 or <code class="computeroutput"><a class="link" href="../BOOST_COPYABLE_AND_MOVABLE.html" title="Macro BOOST_COPYABLE_AND_MOVABLE">BOOST_COPYABLE_AND_MOVABLE</a></code>, 52 these macros define conversion operators to references to <code class="computeroutput"><span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span></code>: 53 </p> 54<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)\</span> 55 <span class="keyword">public</span><span class="special">:\</span> 56 <span class="keyword">operator</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">TYPE</span><span class="special">>&()</span> <span class="special">\</span> 57 <span class="special">{</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">static_cast</span><span class="special"><</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">TYPE</span><span class="special">>*</span> <span class="special">>(</span><span class="keyword">this</span><span class="special">);</span> <span class="special">}\</span> 58 <span class="keyword">operator</span> <span class="keyword">const</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">TYPE</span><span class="special">>&()</span> <span class="keyword">const</span> <span class="special">\</span> 59 <span class="special">{</span> <span class="keyword">return</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">const</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">TYPE</span><span class="special">>*</span> <span class="special">>(</span><span class="keyword">this</span><span class="special">);</span> <span class="special">}\</span> 60 <span class="keyword">private</span><span class="special">:\</span> 61 <span class="comment">//More stuff...</span> 62</pre> 63<p> 64 <code class="computeroutput"><a class="link" href="../BOOST_MOVABL_1_3_26_20_7_3.html" title="Macro BOOST_MOVABLE_BUT_NOT_COPYABLE">BOOST_MOVABLE_BUT_NOT_COPYABLE</a></code> 65 also declares a private copy constructor and assignment. <code class="computeroutput"><a class="link" href="../BOOST_COPYABLE_AND_MOVABLE.html" title="Macro BOOST_COPYABLE_AND_MOVABLE">BOOST_COPYABLE_AND_MOVABLE</a></code> 66 defines a non-const copy constructor <code class="computeroutput"><span class="identifier">TYPE</span> 67 <span class="special">&</span><span class="keyword">operator</span><span class="special">=(</span><span class="identifier">TYPE</span><span class="special">&)</span></code> 68 that forwards to a const version: 69 </p> 70<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)\</span> 71 <span class="keyword">public</span><span class="special">:\</span> 72 <span class="identifier">TYPE</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">TYPE</span> <span class="special">&</span><span class="identifier">t</span><span class="special">)\</span> 73 <span class="special">{</span> <span class="keyword">this</span><span class="special">-></span><span class="keyword">operator</span><span class="special">=(</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">const</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">TYPE</span><span class="special">></span> <span class="special">&>(</span><span class="keyword">const_cast</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">TYPE</span> <span class="special">&>(</span><span class="identifier">t</span><span class="special">)));</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;}\</span> 74 <span class="comment">//More stuff...</span> 75</pre> 76<p> 77 In C++0x compilers <code class="computeroutput"><span class="identifier">BOOST_COPYABLE_AND_MOVABLE</span></code> 78 expands to nothing and <code class="computeroutput"><span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span></code> 79 declares copy constructor and assigment operator private. 80 </p> 81<p> 82 When users define the <code class="computeroutput"><a class="link" href="../BOOST_RV_REF.html" title="Macro BOOST_RV_REF">BOOST_RV_REF</a></code> 83 overload of a copy constructor/assignment, in C++0x compilers it is expanded 84 to a rvalue reference (<code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span></code>) 85 overload and in C++03 compilers it is expanded to a <code class="computeroutput"><span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> 86 <span class="special">&</span></code> overload: 87 </p> 88<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span> <span class="identifier">TYPE</span> <span class="special">>&</span> <span class="special">\</span> 89</pre> 90<p> 91 When users define the <code class="computeroutput"><a class="link" href="../BOOST_COPY_ASSIGN_REF.html" title="Macro BOOST_COPY_ASSIGN_REF">BOOST_COPY_ASSIGN_REF</a></code> 92 overload, it is expanded to a usual copy assignment (<code class="computeroutput"><span class="keyword">const</span> 93 <span class="identifier">T</span> <span class="special">&</span></code>) 94 overload in C++0x compilers and to a <code class="computeroutput"><span class="keyword">const</span> 95 <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span> <span class="special">&</span></code> 96 overload in C++03 compilers: 97 </p> 98<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_COPY_ASSIGN_REF</span><span class="special">(</span><span class="identifier">TYPE</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span> <span class="identifier">TYPE</span> <span class="special">>&</span> 99</pre> 100<p> 101 As seen, in <span class="bold"><strong>Boost.Move</strong></span> generates efficient 102 and clean code for C++0x move semantics, without modifying any resolution overload. 103 For C++03 compilers when overload resolution is performed these are the bindings: 104 </p> 105<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 106<li class="listitem"> 107 a) non-const rvalues (e.g.: temporaries), bind to <code class="computeroutput"><span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span> <span class="identifier">TYPE</span> <span class="special">>&</span></code> 108 </li> 109<li class="listitem"> 110 b) const rvalue and lvalues, bind to <code class="computeroutput"><span class="keyword">const</span> 111 <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span> <span class="identifier">TYPE</span> <span class="special">>&</span></code> 112 </li> 113<li class="listitem"> 114 c) non-const lvalues (e.g. non-const references) bind to <code class="computeroutput"><span class="identifier">TYPE</span><span class="special">&</span></code> 115 </li> 116</ul></div> 117<p> 118 The library does not define the equivalent of <code class="computeroutput"><a class="link" href="../BOOST_COPY_ASSIGN_REF.html" title="Macro BOOST_COPY_ASSIGN_REF">BOOST_COPY_ASSIGN_REF</a></code> 119 for copy construction (say, <code class="computeroutput"><span class="identifier">BOOST_COPY_CTOR_REF</span></code>) 120 because nearly all modern compilers implement RVO and this is much more efficient 121 than any move emulation. <code class="computeroutput"><a class="link" href="../boost/move_1_3_26_20_12_1_1.html" title="Function template move">move</a></code> 122 just casts <code class="computeroutput"><span class="identifier">TYPE</span> <span class="special">&</span></code> 123 into <code class="computeroutput"><span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">TYPE</span><span class="special">></span> <span class="special">&</span></code>. 124 </p> 125<p> 126 Here's an example that demostrates how different rlvalue objects bind to <code class="computeroutput"><span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span></code> references in the presence of three overloads 127 and the conversion operators in C++03 compilers: 128 </p> 129<p> 130</p> 131<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">move</span><span class="special">/</span><span class="identifier">core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 132<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 133 134<span class="keyword">class</span> <span class="identifier">sink_tester</span> 135<span class="special">{</span> 136 <span class="keyword">public</span><span class="special">:</span> <span class="comment">//conversions provided by BOOST_COPYABLE_AND_MOVABLE</span> 137 <span class="keyword">operator</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">sink_tester</span><span class="special">>&()</span> 138 <span class="special">{</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">static_cast</span><span class="special"><</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">sink_tester</span><span class="special">>*</span> <span class="special">>(</span><span class="keyword">this</span><span class="special">);</span> <span class="special">}</span> 139 <span class="keyword">operator</span> <span class="keyword">const</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">sink_tester</span><span class="special">>&()</span> <span class="keyword">const</span> 140 <span class="special">{</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">const</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">sink_tester</span><span class="special">>*</span> <span class="special">>(</span><span class="keyword">this</span><span class="special">);</span> <span class="special">}</span> 141<span class="special">};</span> 142 143<span class="comment">//Functions returning different r/lvalue types</span> 144 <span class="identifier">sink_tester</span> <span class="identifier">rvalue</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">sink_tester</span><span class="special">();</span> <span class="special">}</span> 145<span class="keyword">const</span> <span class="identifier">sink_tester</span> <span class="identifier">const_rvalue</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">sink_tester</span><span class="special">();</span> <span class="special">}</span> 146 <span class="identifier">sink_tester</span> <span class="special">&</span> <span class="identifier">lvalue</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">static</span> <span class="identifier">sink_tester</span> <span class="identifier">lv</span><span class="special">;</span> <span class="keyword">return</span> <span class="identifier">lv</span><span class="special">;</span> <span class="special">}</span> 147<span class="keyword">const</span> <span class="identifier">sink_tester</span> <span class="special">&</span> <span class="identifier">const_lvalue</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">sink_tester</span> <span class="identifier">clv</span> <span class="special">=</span> <span class="identifier">sink_tester</span><span class="special">();</span> <span class="keyword">return</span> <span class="identifier">clv</span><span class="special">;</span> <span class="special">}</span> 148 149<span class="comment">//BOOST_RV_REF overload</span> 150<span class="keyword">void</span> <span class="identifier">sink</span><span class="special">(::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">sink_tester</span><span class="special">></span> <span class="special">&)</span> <span class="special">{</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"non-const rvalue catched"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="special">}</span> 151<span class="comment">//BOOST_COPY_ASSIGN_REF overload</span> 152<span class="keyword">void</span> <span class="identifier">sink</span><span class="special">(</span><span class="keyword">const</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">rv</span><span class="special"><</span><span class="identifier">sink_tester</span><span class="special">></span> <span class="special">&){</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"const (r-l)value catched"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="special">}</span> 153<span class="comment">//Overload provided by BOOST_COPYABLE_AND_MOVABLE</span> 154<span class="keyword">void</span> <span class="identifier">sink</span><span class="special">(</span><span class="identifier">sink_tester</span> <span class="special">&)</span> <span class="special">{</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"non-const lvalue catched"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="special">}</span> 155 156<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 157<span class="special">{</span> 158 <span class="identifier">sink</span><span class="special">(</span><span class="identifier">const_rvalue</span><span class="special">());</span> <span class="comment">//"const (r-l)value catched"</span> 159 <span class="identifier">sink</span><span class="special">(</span><span class="identifier">const_lvalue</span><span class="special">());</span> <span class="comment">//"const (r-l)value catched"</span> 160 <span class="identifier">sink</span><span class="special">(</span><span class="identifier">lvalue</span><span class="special">());</span> <span class="comment">//"non-const lvalue catched"</span> 161 <span class="identifier">sink</span><span class="special">(</span><span class="identifier">rvalue</span><span class="special">());</span> <span class="comment">//"non-const rvalue catched"</span> 162 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 163<span class="special">}</span> 164</pre> 165<p> 166 </p> 167</div> 168<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 169<td align="left"></td> 170<td align="right"><div class="copyright-footer">Copyright © 2008-2014 Ion Gaztanaga<p> 171 Distributed under the Boost Software License, Version 1.0. (See accompanying 172 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 173 </p> 174</div></td> 175</tr></table> 176<hr> 177<div class="spirit-nav"> 178<a accesskey="p" href="emulation_limitations.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../move.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="thanks_to.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 179</div> 180</body> 181</html> 182
