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diff --git a/doc/html/move/implementing_movable_classes.html b/doc/html/move/implementing_movable_classes.html new file mode 100755 index 0000000000..07fd96ad2c --- /dev/null +++ b/doc/html/move/implementing_movable_classes.html @@ -0,0 +1,246 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>Implementing copyable and movable classes</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="introduction.html" title="Introduction"> +<link rel="next" href="composition_inheritance.html" title="Composition or inheritance"> +</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="introduction.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="composition_inheritance.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.implementing_movable_classes"></a><a class="link" href="implementing_movable_classes.html" title="Implementing copyable and movable classes">Implementing copyable + and movable classes</a> +</h2></div></div></div> +<div class="toc"><dl> +<dt><span class="section"><a href="implementing_movable_classes.html#move.implementing_movable_classes.copyable_and_movable_cpp0x">Copyable + and movable classes in C++0x</a></span></dt> +<dt><span class="section"><a href="implementing_movable_classes.html#move.implementing_movable_classes.copyable_and_movable_cpp03">Copyable + and movable classes in portable syntax for both C++03 and C++0x compilers</a></span></dt> +</dl></div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="move.implementing_movable_classes.copyable_and_movable_cpp0x"></a><a class="link" href="implementing_movable_classes.html#move.implementing_movable_classes.copyable_and_movable_cpp0x" title="Copyable and movable classes in C++0x">Copyable + and movable classes in C++0x</a> +</h3></div></div></div> +<p> + Consider a simple handle class that owns a resource and also provides copy + semantics (copy constructor and assignment). For example a <code class="computeroutput"><span class="identifier">clone_ptr</span></code> might own a pointer, and call + <code class="computeroutput"><span class="identifier">clone</span><span class="special">()</span></code> + on it for copying purposes: + </p> +<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> +<span class="keyword">class</span> <span class="identifier">clone_ptr</span> +<span class="special">{</span> + <span class="keyword">private</span><span class="special">:</span> + <span class="identifier">T</span><span class="special">*</span> <span class="identifier">ptr</span><span class="special">;</span> + + <span class="keyword">public</span><span class="special">:</span> + <span class="comment">// construction</span> + <span class="keyword">explicit</span> <span class="identifier">clone_ptr</span><span class="special">(</span><span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">ptr</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">{}</span> + + <span class="comment">// destruction</span> + <span class="special">~</span><span class="identifier">clone_ptr</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">delete</span> <span class="identifier">ptr</span><span class="special">;</span> <span class="special">}</span> + + <span class="comment">// copy semantics</span> + <span class="identifier">clone_ptr</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">clone_ptr</span><span class="special">&</span> <span class="identifier">p</span><span class="special">)</span> + <span class="special">:</span> <span class="identifier">ptr</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span> <span class="special">?</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">-></span><span class="identifier">clone</span><span class="special">()</span> <span class="special">:</span> <span class="number">0</span><span class="special">)</span> <span class="special">{}</span> + + <span class="identifier">clone_ptr</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="identifier">clone_ptr</span><span class="special">&</span> <span class="identifier">p</span><span class="special">)</span> + <span class="special">{</span> + <span class="keyword">if</span> <span class="special">(</span><span class="keyword">this</span> <span class="special">!=</span> <span class="special">&</span><span class="identifier">p</span><span class="special">)</span> + <span class="special">{</span> + <span class="identifier">T</span> <span class="special">*</span><span class="identifier">p</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span> <span class="special">?</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">-></span><span class="identifier">clone</span><span class="special">()</span> <span class="special">:</span> <span class="number">0</span><span class="special">;</span> + <span class="keyword">delete</span> <span class="identifier">ptr</span><span class="special">;</span> + <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">p</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="special">}</span> + + <span class="comment">// move semantics</span> + <span class="identifier">clone_ptr</span><span class="special">(</span><span class="identifier">clone_ptr</span><span class="special">&&</span> <span class="identifier">p</span><span class="special">)</span> + <span class="special">:</span> <span class="identifier">ptr</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> + + <span class="identifier">clone_ptr</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">clone_ptr</span><span class="special">&&</span> <span class="identifier">p</span><span class="special">)</span> + <span class="special">{</span> + <span class="identifier">std</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">ptr</span><span class="special">,</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">);</span> + <span class="keyword">delete</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">;</span> + <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="number">0</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">// Other operations...</span> +<span class="special">};</span> +</pre> +<p> + <code class="computeroutput"><span class="identifier">clone_ptr</span></code> has expected copy + constructor and assignment semantics, duplicating resources when copying. + Note that copy constructing or assigning a <code class="computeroutput"><span class="identifier">clone_ptr</span></code> + is a relatively expensive operation: + </p> +<p> +</p> +<pre class="programlisting"><span class="identifier">clone_ptr</span><span class="special"><</span><span class="identifier">Base</span><span class="special">></span> <span class="identifier">p1</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">Derived</span><span class="special">());</span> +<span class="comment">// ...</span> +<span class="identifier">clone_ptr</span><span class="special"><</span><span class="identifier">Base</span><span class="special">></span> <span class="identifier">p2</span> <span class="special">=</span> <span class="identifier">p1</span><span class="special">;</span> <span class="comment">// p2 and p1 each own their own pointer</span> +</pre> +<p> + </p> +<p> + <code class="computeroutput"><span class="identifier">clone_ptr</span></code> is code that you + might find in today's books on C++, except for the part marked as <code class="computeroutput"><span class="identifier">move</span> <span class="identifier">semantics</span></code>. + That part is implemented in terms of C++0x <code class="computeroutput"><span class="identifier">rvalue</span> + <span class="identifier">references</span></code>. You can find some good + introduction and tutorials on rvalue references in these papers: + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem"> + <a href="http://www.artima.com/cppsource/rvalue.html" target="_top"><span class="emphasis"><em>A + Brief Introduction to Rvalue References</em></span></a> + </li> +<li class="listitem"> + <a href="http://blogs.msdn.com/vcblog/archive/2009/02/03/rvalue-references-c-0x-features-in-vc10-part-2.aspx" target="_top"><span class="emphasis"><em>Rvalue + References: C++0x Features in VC10, Part 2</em></span></a> + </li> +</ul></div> +<p> + When the source of the copy is known to be an <code class="computeroutput"><span class="identifier">rvalue</span></code> + (e.g.: a temporary object), one can avoid the potentially expensive <code class="computeroutput"><span class="identifier">clone</span><span class="special">()</span></code> + operation by pilfering source's pointer (no one will notice!). The move constructor + above does exactly that, leaving the rvalue in a default constructed state. + The move assignment operator simply does the same freeing old resources. + </p> +<p> + Now when code tries to copy an rvalue <code class="computeroutput"><span class="identifier">clone_ptr</span></code>, + or if that code explicitly gives permission to consider the source of the + copy an rvalue (using <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span></code>), + the operation will execute much faster. + </p> +<p> +</p> +<pre class="programlisting"><span class="identifier">clone_ptr</span><span class="special"><</span><span class="identifier">Base</span><span class="special">></span> <span class="identifier">p1</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">Derived</span><span class="special">());</span> +<span class="comment">// ...</span> +<span class="identifier">clone_ptr</span><span class="special"><</span><span class="identifier">Base</span><span class="special">></span> <span class="identifier">p2</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">p1</span><span class="special">);</span> <span class="comment">// p2 now owns the pointer instead of p1</span> +<span class="identifier">p2</span> <span class="special">=</span> <span class="identifier">clone_ptr</span><span class="special"><</span><span class="identifier">Base</span><span class="special">>(</span><span class="keyword">new</span> <span class="identifier">Derived</span><span class="special">());</span> <span class="comment">// temporary is moved to p2</span> +<span class="special">}</span> +</pre> +<p> + </p> +</div> +<div class="section"> +<div class="titlepage"><div><div><h3 class="title"> +<a name="move.implementing_movable_classes.copyable_and_movable_cpp03"></a><a class="link" href="implementing_movable_classes.html#move.implementing_movable_classes.copyable_and_movable_cpp03" title="Copyable and movable classes in portable syntax for both C++03 and C++0x compilers">Copyable + and movable classes in portable syntax for both C++03 and C++0x compilers</a> +</h3></div></div></div> +<p> + Many aspects of move semantics can be emulated for compilers not supporting + <code class="computeroutput"><span class="identifier">rvalue</span> <span class="identifier">references</span></code> + and <span class="bold"><strong>Boost.Move</strong></span> offers tools for that purpose. + With <span class="bold"><strong>Boost.Move</strong></span> we can write <code class="computeroutput"><span class="identifier">clone_ptr</span></code> so that it will work both in + compilers with rvalue references and those who conform to C++03. You just + need to follow these simple steps: + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem"> + Put the following macro in the <span class="bold"><strong>private</strong></span> + section: <code class="computeroutput"><a class="link" href="../BOOST_COPYABLE_AND_MOVABLE.html" title="Macro BOOST_COPYABLE_AND_MOVABLE">BOOST_COPYABLE_AND_MOVABLE(classname)</a></code> + </li> +<li class="listitem"> + Left copy constructor as is. + </li> +<li class="listitem"> + Write a copy assignment taking the parameter as <code class="computeroutput"><a class="link" href="../BOOST_COPY_ASSIGN_REF.html" title="Macro BOOST_COPY_ASSIGN_REF">BOOST_COPY_ASSIGN_REF(classname)</a></code> + </li> +<li class="listitem"> + Write a move constructor and a move assignment taking the parameter as + <code class="computeroutput"><a class="link" href="../BOOST_RV_REF.html" title="Macro BOOST_RV_REF">BOOST_RV_REF(classname)</a></code> + </li> +</ul></div> +<p> + Let's see how are applied to <code class="computeroutput"><span class="identifier">clone_ptr</span></code>: + </p> +<p> +</p> +<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> +<span class="keyword">class</span> <span class="identifier">clone_ptr</span> +<span class="special">{</span> + <span class="keyword">private</span><span class="special">:</span> + <span class="comment">// Mark this class copyable and movable</span> + <span class="identifier">BOOST_COPYABLE_AND_MOVABLE</span><span class="special">(</span><span class="identifier">clone_ptr</span><span class="special">)</span> + <span class="identifier">T</span><span class="special">*</span> <span class="identifier">ptr</span><span class="special">;</span> + + <span class="keyword">public</span><span class="special">:</span> + <span class="comment">// Construction</span> + <span class="keyword">explicit</span> <span class="identifier">clone_ptr</span><span class="special">(</span><span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">ptr</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">{}</span> + + <span class="comment">// Destruction</span> + <span class="special">~</span><span class="identifier">clone_ptr</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">delete</span> <span class="identifier">ptr</span><span class="special">;</span> <span class="special">}</span> + + <span class="identifier">clone_ptr</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">clone_ptr</span><span class="special">&</span> <span class="identifier">p</span><span class="special">)</span> <span class="comment">// Copy constructor (as usual)</span> + <span class="special">:</span> <span class="identifier">ptr</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span> <span class="special">?</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">-></span><span class="identifier">clone</span><span class="special">()</span> <span class="special">:</span> <span class="number">0</span><span class="special">)</span> <span class="special">{}</span> + + <span class="identifier">clone_ptr</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">clone_ptr</span><span class="special">)</span> <span class="identifier">p</span><span class="special">)</span> <span class="comment">// Copy assignment</span> + <span class="special">{</span> + <span class="keyword">if</span> <span class="special">(</span><span class="keyword">this</span> <span class="special">!=</span> <span class="special">&</span><span class="identifier">p</span><span class="special">){</span> + <span class="identifier">T</span> <span class="special">*</span><span class="identifier">tmp_p</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span> <span class="special">?</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">-></span><span class="identifier">clone</span><span class="special">()</span> <span class="special">:</span> <span class="number">0</span><span class="special">;</span> + <span class="keyword">delete</span> <span class="identifier">ptr</span><span class="special">;</span> + <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">tmp_p</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="special">}</span> + + <span class="comment">//Move semantics...</span> + <span class="identifier">clone_ptr</span><span class="special">(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">clone_ptr</span><span class="special">)</span> <span class="identifier">p</span><span class="special">)</span> <span class="comment">//Move constructor</span> + <span class="special">:</span> <span class="identifier">ptr</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> + + <span class="identifier">clone_ptr</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">clone_ptr</span><span class="special">)</span> <span class="identifier">p</span><span class="special">)</span> <span class="comment">//Move assignment</span> + <span class="special">{</span> + <span class="keyword">if</span> <span class="special">(</span><span class="keyword">this</span> <span class="special">!=</span> <span class="special">&</span><span class="identifier">p</span><span class="special">){</span> + <span class="keyword">delete</span> <span class="identifier">ptr</span><span class="special">;</span> + <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span><span class="special">;</span> + <span class="identifier">p</span><span class="special">.</span><span class="identifier">ptr</span> <span class="special">=</span> <span class="number">0</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="special">}</span> +<span class="special">};</span> +</pre> +<p> + </p> +</div> +<p> + <span class="bold"><strong>Question</strong></span>: What about types that don't own + resources? (E.g. <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span></code>?) + </p> +<p> + No work needs to be done in that case. The copy constructor is already optimal. + </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="introduction.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="composition_inheritance.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |