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diff --git a/doc/html/move/composition_inheritance.html b/doc/html/move/composition_inheritance.html new file mode 100755 index 0000000000..0018d39fbc --- /dev/null +++ b/doc/html/move/composition_inheritance.html @@ -0,0 +1,154 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>Composition or inheritance</title> +<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.76.1"> +<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> +<link rel="up" href="../move.html" title="Chapter 16. Boost.Move"> +<link rel="prev" href="implementing_movable_classes.html" title="Implementing copyable and movable classes"> +<link rel="next" href="movable_only_classes.html" title="Movable but Non-Copyable Types"> +</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="implementing_movable_classes.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="movable_only_classes.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +<div class="section"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="move.composition_inheritance"></a><a class="link" href="composition_inheritance.html" title="Composition or inheritance">Composition or inheritance</a> +</h2></div></div></div> +<p> + For classes made up of other classes (via either composition or inheritance), + the move constructor and move assignment can be easily coded using the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span></code> + function: + </p> +<p> +</p> +<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">Base</span> +<span class="special">{</span> + <span class="identifier">BOOST_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">Base</span><span class="special">)</span> + + <span class="keyword">public</span><span class="special">:</span> + <span class="identifier">Base</span><span class="special">(){}</span> + + <span class="identifier">Base</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Base</span> <span class="special">&</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{/**/}</span> <span class="comment">// Copy ctor</span> + + <span class="identifier">Base</span><span class="special">(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">Base</span><span class="special">)</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{/**/}</span> <span class="comment">// Move ctor</span> + + <span class="identifier">Base</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">Base</span><span class="special">)</span> <span class="identifier">x</span><span class="special">)</span> + <span class="special">{/**/</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;}</span> <span class="comment">// Move assign</span> + + <span class="identifier">Base</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_COPY_ASSIGN_REF</span><span class="special">(</span><span class="identifier">Base</span><span class="special">)</span> <span class="identifier">x</span><span class="special">)</span> + <span class="special">{/**/</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;}</span> <span class="comment">// Copy assign</span> + + <span class="keyword">virtual</span> <span class="identifier">Base</span> <span class="special">*</span><span class="identifier">clone</span><span class="special">()</span> <span class="keyword">const</span> + <span class="special">{</span> <span class="keyword">return</span> <span class="keyword">new</span> <span class="identifier">Base</span><span class="special">(*</span><span class="keyword">this</span><span class="special">);</span> <span class="special">}</span> +<span class="special">};</span> + +<span class="keyword">class</span> <span class="identifier">Member</span> +<span class="special">{</span> + <span class="identifier">BOOST_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">Member</span><span class="special">)</span> + + <span class="keyword">public</span><span class="special">:</span> + <span class="identifier">Member</span><span class="special">(){}</span> + + <span class="comment">// Compiler-generated copy constructor...</span> + + <span class="identifier">Member</span><span class="special">(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">Member</span><span class="special">))</span> <span class="special">{/**/}</span> <span class="comment">// Move ctor</span> + + <span class="identifier">Member</span> <span class="special">&</span><span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">Member</span><span class="special">))</span> <span class="comment">// Move assign</span> + <span class="special">{/**/</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span> <span class="special">}</span> + + <span class="identifier">Member</span> <span class="special">&</span><span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_COPY_ASSIGN_REF</span><span class="special">(</span><span class="identifier">Member</span><span class="special">))</span> <span class="comment">// Copy assign</span> + <span class="special">{/**/</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span> <span class="special">}</span> +<span class="special">};</span> + +<span class="keyword">class</span> <span class="identifier">Derived</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">Base</span> +<span class="special">{</span> + <span class="identifier">BOOST_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">Derived</span><span class="special">)</span> + <span class="identifier">Member</span> <span class="identifier">mem_</span><span class="special">;</span> + + <span class="keyword">public</span><span class="special">:</span> + <span class="identifier">Derived</span><span class="special">(){}</span> + + <span class="comment">// Compiler-generated copy constructor...</span> + + <span class="identifier">Derived</span><span class="special">(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">Derived</span><span class="special">)</span> <span class="identifier">x</span><span class="special">)</span> <span class="comment">// Move ctor</span> + <span class="special">:</span> <span class="identifier">Base</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="keyword">static_cast</span><span class="special"><</span><span class="identifier">Base</span><span class="special">&>(</span><span class="identifier">x</span><span class="special">))),</span> + <span class="identifier">mem_</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">x</span><span class="special">.</span><span class="identifier">mem_</span><span class="special">))</span> <span class="special">{</span> <span class="special">}</span> + + <span class="identifier">Derived</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">Derived</span><span class="special">)</span> <span class="identifier">x</span><span class="special">)</span> <span class="comment">// Move assign</span> + <span class="special">{</span> + <span class="identifier">Base</span><span class="special">::</span><span class="keyword">operator</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="keyword">static_cast</span><span class="special"><</span><span class="identifier">Base</span><span class="special">&>(</span><span class="identifier">x</span><span class="special">)));</span> + <span class="identifier">mem_</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">x</span><span class="special">.</span><span class="identifier">mem_</span><span class="special">);</span> + <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span> + <span class="special">}</span> + + <span class="identifier">Derived</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_COPY_ASSIGN_REF</span><span class="special">(</span><span class="identifier">Derived</span><span class="special">)</span> <span class="identifier">x</span><span class="special">)</span> <span class="comment">// Copy assign</span> + <span class="special">{</span> + <span class="identifier">Base</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="identifier">Base</span><span class="special">&>(</span><span class="identifier">x</span><span class="special">));</span> + <span class="identifier">mem_</span> <span class="special">=</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">mem_</span><span class="special">;</span> + <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span> + <span class="special">}</span> + <span class="comment">// ...</span> +<span class="special">};</span> +</pre> +<p> + </p> +<div class="important"><table border="0" summary="Important"> +<tr> +<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../doc/src/images/important.png"></td> +<th align="left">Important</th> +</tr> +<tr><td align="left" valign="top"><p> + Due to limitations in the emulation code, a cast to <code class="computeroutput"><span class="identifier">Base</span> + <span class="special">&</span></code> is needed before moving the + base part in the move constructor and call Base's move constructor instead + of the copy constructor. + </p></td></tr> +</table></div> +<p> + Each subobject will now be treated individually, calling move to bind to the + subobject's move constructors and move assignment operators. <code class="computeroutput"><span class="identifier">Member</span></code> has move operations coded (just like + our earlier <code class="computeroutput"><span class="identifier">clone_ptr</span></code> example) + which will completely avoid the tremendously more expensive copy operations: + </p> +<p> +</p> +<pre class="programlisting"><span class="identifier">Derived</span> <span class="identifier">d</span><span class="special">;</span> +<span class="identifier">Derived</span> <span class="identifier">d2</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">d</span><span class="special">));</span> +<span class="identifier">d2</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">d</span><span class="special">);</span> +</pre> +<p> + </p> +<p> + Note above that the argument x is treated as a lvalue reference. That's why + it is necessary to say <code class="computeroutput"><span class="identifier">move</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> + instead of just x when passing down to the base class. This is a key safety + feature of move semantics designed to prevent accidently moving twice from + some named variable. All moves from lvalues occur explicitly. + </p> +</div> +<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> +<td align="left"></td> +<td align="right"><div class="copyright-footer">Copyright © 2008-2010 Ion Gaztanaga<p> + Distributed under the Boost Software License, Version 1.0. (See accompanying + 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>) + </p> +</div></td> +</tr></table> +<hr> +<div class="spirit-nav"> +<a accesskey="p" href="implementing_movable_classes.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="movable_only_classes.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |