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diff --git a/doc/html/move/movable_only_classes.html b/doc/html/move/movable_only_classes.html new file mode 100755 index 0000000000..42e79f5d40 --- /dev/null +++ b/doc/html/move/movable_only_classes.html @@ -0,0 +1,131 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> +<title>Movable but Non-Copyable Types</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="composition_inheritance.html" title="Composition or inheritance"> +<link rel="next" href="move_and_containers.html" title="Containers and move semantics"> +</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="composition_inheritance.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="move_and_containers.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.movable_only_classes"></a><a class="link" href="movable_only_classes.html" title="Movable but Non-Copyable Types">Movable but Non-Copyable Types</a> +</h2></div></div></div> +<p> + Some types are not amenable to copy semantics but can still be made movable. + For example: + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem"> + <code class="computeroutput"><span class="identifier">unique_ptr</span></code> (non-shared, + non-copyable ownership) + </li> +<li class="listitem"> + A type representing a thread of execution + </li> +<li class="listitem"> + A type representing a file descriptor + </li> +</ul></div> +<p> + By making such types movable (though still non-copyable) their utility is tremendously + increased. Movable but non-copyable types can be returned by value from factory + functions: + </p> +<pre class="programlisting"><span class="identifier">file_descriptor</span> <span class="identifier">create_file</span><span class="special">(/*</span> <span class="special">...</span> <span class="special">*/);</span> +<span class="comment">//...</span> +<span class="identifier">file_descriptor</span> <span class="identifier">data_file</span><span class="special">;</span> +<span class="comment">//...</span> +<span class="identifier">data_file</span> <span class="special">=</span> <span class="identifier">create_file</span><span class="special">(/*</span> <span class="special">...</span> <span class="special">*/);</span> <span class="comment">// No copies!</span> +</pre> +<p> + In the above example, the underlying file handle is passed from object to object, + as long as the source <code class="computeroutput"><span class="identifier">file_descriptor</span></code> + is an rvalue. At all times, there is still only one underlying file handle, + and only one <code class="computeroutput"><span class="identifier">file_descriptor</span></code> + owns it at a time. + </p> +<p> + To write a movable but not copyable type in portable syntax, you 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_MOVABLE_BUT_NOT_COPYABLE.html" title="Macro BOOST_MOVABLE_BUT_NOT_COPYABLE">BOOST_MOVABLE_BUT_NOT_COPYABLE(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> + Here's the definition of <code class="computeroutput"><span class="identifier">file</span> <span class="identifier">descriptor</span></code> using portable syntax: + </p> +<p> +</p> +<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">move</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> +<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">stdexcept</span><span class="special">></span> + +<span class="keyword">class</span> <span class="identifier">file_descriptor</span> +<span class="special">{</span> + <span class="keyword">int</span> <span class="identifier">os_descr_</span><span class="special">;</span> + + <span class="keyword">private</span><span class="special">:</span> + <span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">file_descriptor</span><span class="special">)</span> + + <span class="keyword">public</span><span class="special">:</span> + <span class="keyword">explicit</span> <span class="identifier">file_descriptor</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">filename</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> <span class="comment">//Constructor</span> + <span class="special">:</span> <span class="identifier">os_descr_</span><span class="special">(</span><span class="identifier">filename</span> <span class="special">?</span> <span class="identifier">operating_system_open_file</span><span class="special">(</span><span class="identifier">filename</span><span class="special">)</span> <span class="special">:</span> <span class="number">0</span><span class="special">)</span> + <span class="special">{</span> <span class="keyword">if</span><span class="special">(!</span><span class="identifier">os_descr_</span><span class="special">)</span> <span class="keyword">throw</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span><span class="special">(</span><span class="string">"file not found"</span><span class="special">);</span> <span class="special">}</span> + + <span class="special">~</span><span class="identifier">file_descriptor</span><span class="special">()</span> <span class="comment">//Destructor</span> + <span class="special">{</span> <span class="keyword">if</span><span class="special">(!</span><span class="identifier">os_descr_</span><span class="special">)</span> <span class="identifier">operating_system_close_file</span><span class="special">(</span><span class="identifier">os_descr_</span><span class="special">);</span> <span class="special">}</span> + + <span class="identifier">file_descriptor</span><span class="special">(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">file_descriptor</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">os_descr_</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">os_descr_</span><span class="special">)</span> + <span class="special">{</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">os_descr_</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> + + <span class="identifier">file_descriptor</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">file_descriptor</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="keyword">if</span><span class="special">(!</span><span class="identifier">os_descr_</span><span class="special">)</span> <span class="identifier">operating_system_close_file</span><span class="special">(</span><span class="identifier">os_descr_</span><span class="special">);</span> + <span class="identifier">os_descr_</span> <span class="special">=</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">os_descr_</span><span class="special">;</span> + <span class="identifier">x</span><span class="special">.</span><span class="identifier">os_descr_</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="keyword">bool</span> <span class="identifier">empty</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">os_descr_</span> <span class="special">==</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> +<span class="special">};</span> +</pre> +<p> + </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="composition_inheritance.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="move_and_containers.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> +</div> +</body> +</html> |