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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="intrusive.clone_from"></a><a class="link" href="clone_from.html" title="Cloning Boost.Intrusive containers">Cloning Boost.Intrusive containers</a> |
| </h2></div></div></div> |
| <p> |
| As previously mentioned, <span class="bold"><strong>Boost.Intrusive</strong></span> containers |
| are <span class="bold"><strong>non-copyable and non-assignable</strong></span>, because |
| intrusive containers don't allocate memory at all. To implement a copy-constructor |
| or assignment operator, the user must clone one by one all the elements of |
| the container and insert them in another intrusive container. However, cloning |
| by hand is usually more inefficient than a member cloning function and a specialized |
| cloning function can offer more guarantees than the manual cloning (better |
| exception safety guarantees, for example). |
| </p> |
| <p> |
| To ease the implementation of copy constructors and assignment operators of |
| classes containing <span class="bold"><strong>Boost.Intrusive</strong></span> containers, |
| all <span class="bold"><strong>Boost.Intrusive</strong></span> containers offer a special |
| cloning function called <code class="computeroutput"><span class="identifier">clone_from</span></code>. |
| </p> |
| <p> |
| Apart from the container to be cloned, <code class="computeroutput"><span class="identifier">clone_from</span></code> |
| takes two function objects as arguments. For example, consider the <code class="computeroutput"><span class="identifier">clone_from</span></code> member function of <code class="computeroutput"><a class="link" href="../boost/intrusive/list.html" title="Class template list">list</a></code>: |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Cloner</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Disposer</span><span class="special">></span> |
| <span class="keyword">void</span> <span class="identifier">clone_from</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">list</span> <span class="special">&</span><span class="identifier">src</span><span class="special">,</span> <span class="identifier">Cloner</span> <span class="identifier">cloner</span><span class="special">,</span> <span class="identifier">Disposer</span> <span class="identifier">disposer</span><span class="special">);</span> |
| </pre> |
| <p> |
| This function will make <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> |
| a clone of <code class="computeroutput"><span class="identifier">src</span></code>. Let's explain |
| the arguments: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| The first parameter is the list to be cloned. |
| </li> |
| <li class="listitem"> |
| The second parameter is a function object that will clone <code class="computeroutput"><span class="identifier">value_type</span></code> objects and return a pointer |
| to the clone. It must implement the following function: <code class="computeroutput"><span class="identifier">pointer</span> |
| <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">value_type</span> |
| <span class="special">&)</span></code>. |
| </li> |
| <li class="listitem"> |
| The second parameter is a function object that will dispose <code class="computeroutput"><span class="identifier">value_type</span></code> objects. It's used first to |
| empty the container before cloning and to dispose the elements if an exception |
| is thrown. |
| </li> |
| </ul></div> |
| <p> |
| The cloning function works as follows: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| First it clears and disposes all the elements from *this using the disposer |
| function object. |
| </li> |
| <li class="listitem"> |
| After that it starts cloning all the elements of the source container using |
| the cloner function object. |
| </li> |
| <li class="listitem"> |
| If any operation in the cloning function (for example, the cloner function |
| object) throws, all the constructed elements are disposed using the disposer |
| function object. |
| </li> |
| </ul></div> |
| <p> |
| Here is an example of <code class="computeroutput"><span class="identifier">clone_from</span></code>: |
| </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">intrusive</span><span class="special">/</span><span class="identifier">list</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">iostream</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span> |
| |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive</span><span class="special">;</span> |
| |
| <span class="comment">//A class that can be inserted in an intrusive list |
| </span><span class="keyword">class</span> <span class="identifier">my_class</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">list_base_hook</span><span class="special"><></span> |
| <span class="special">{</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span><span class="keyword">const</span> <span class="identifier">my_class</span> <span class="special">&</span><span class="identifier">a</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">my_class</span> <span class="special">&</span><span class="identifier">b</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">int_</span> <span class="special">==</span> <span class="identifier">b</span><span class="special">.</span><span class="identifier">int_</span><span class="special">;</span> <span class="special">}</span> |
| |
| <span class="keyword">int</span> <span class="identifier">int_</span><span class="special">;</span> |
| |
| <span class="comment">//... |
| </span><span class="special">};</span> |
| |
| <span class="comment">//Definition of the intrusive list |
| </span><span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">></span> <span class="identifier">my_class_list</span><span class="special">;</span> |
| |
| <span class="comment">//Cloner object function |
| </span><span class="keyword">struct</span> <span class="identifier">new_cloner</span> |
| <span class="special">{</span> |
| <span class="identifier">my_class</span> <span class="special">*</span><span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">my_class</span> <span class="special">&</span><span class="identifier">clone_this</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="keyword">new</span> <span class="identifier">my_class</span><span class="special">(</span><span class="identifier">clone_this</span><span class="special">);</span> <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="comment">//The disposer object function |
| </span><span class="keyword">struct</span> <span class="identifier">delete_disposer</span> |
| <span class="special">{</span> |
| <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">my_class</span> <span class="special">*</span><span class="identifier">delete_this</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">delete</span> <span class="identifier">delete_this</span><span class="special">;</span> <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">MaxElem</span> <span class="special">=</span> <span class="number">100</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">></span> <span class="identifier">nodes</span><span class="special">(</span><span class="identifier">MaxElem</span><span class="special">);</span> |
| |
| <span class="comment">//Fill all the nodes and insert them in the list |
| </span> <span class="identifier">my_class_list</span> <span class="identifier">list</span><span class="special">;</span> |
| |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="identifier">MaxElem</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">].</span><span class="identifier">int_</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> |
| |
| <span class="identifier">list</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">nodes</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">nodes</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> |
| |
| <span class="comment">//Now clone "list" using "new" and "delete" object functions |
| </span> <span class="identifier">my_class_list</span> <span class="identifier">cloned_list</span><span class="special">;</span> |
| <span class="identifier">cloned_list</span><span class="special">.</span><span class="identifier">clone_from</span><span class="special">(</span><span class="identifier">list</span><span class="special">,</span> <span class="identifier">new_cloner</span><span class="special">(),</span> <span class="identifier">delete_disposer</span><span class="special">());</span> |
| |
| <span class="comment">//Test that both are equal |
| </span> <span class="keyword">if</span><span class="special">(</span><span class="identifier">cloned_list</span> <span class="special">!=</span> <span class="identifier">list</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">"Both lists are different"</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="keyword">else</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Both lists are equal"</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="comment">//Don't forget to free the memory from the second list |
| </span> <span class="identifier">cloned_list</span><span class="special">.</span><span class="identifier">clear_and_dispose</span><span class="special">(</span><span class="identifier">delete_disposer</span><span class="special">());</span> |
| <span class="keyword">return</span> <span class="number">0</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 © 2005 Olaf Krzikalla, 2006-2010 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>) |
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