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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="intrusive.function_hooks"></a><a class="link" href="function_hooks.html" title="Using function hooks">Using function hooks</a> |
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| <p> |
| A programmer might find that base or member hooks are not flexible enough in |
| some situations. In some applications it would be optimal to put a hook deep |
| inside a member of a class or just outside the class. <span class="bold"><strong>Boost.Intrusive</strong></span> |
| has an easy option to allow such cases: <code class="computeroutput"><a class="link" href="../boost/intrusive/function_hook.html" title="Struct template function_hook">function_hook</a></code>. |
| </p> |
| <p> |
| This option is similar to <code class="computeroutput"><a class="link" href="../boost/intrusive/member_hook.html" title="Struct template member_hook">member_hook</a></code> |
| or <code class="computeroutput"><a class="link" href="../boost/intrusive/base_hook.html" title="Struct template base_hook">base_hook</a></code>, but |
| the programmer can specify a function object that tells the container how to |
| obtain a hook from a value and vice versa. The programmer just needs to define |
| the following function object: |
| </p> |
| <pre class="programlisting"><span class="comment">//This functor converts between value_type and a hook_type |
| </span><span class="keyword">struct</span> <span class="identifier">Functor</span> |
| <span class="special">{</span> |
| <span class="comment">//Required types |
| </span> <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">hook_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">hook_ptr</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">const_hook_ptr</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">value_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">pointer</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">const_pointer</span><span class="special">;</span> |
| <span class="comment">//Required static functions |
| </span> <span class="keyword">static</span> <span class="identifier">hook_ptr</span> <span class="identifier">to_hook_ptr</span> <span class="special">(</span><span class="identifier">value_type</span> <span class="special">&</span><span class="identifier">value</span><span class="special">);</span> |
| <span class="keyword">static</span> <span class="identifier">const_hook_ptr</span> <span class="identifier">to_hook_ptr</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&</span><span class="identifier">value</span><span class="special">);</span> |
| <span class="keyword">static</span> <span class="identifier">pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">hook_ptr</span> <span class="identifier">n</span><span class="special">);</span> |
| <span class="keyword">static</span> <span class="identifier">const_pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">const_hook_ptr</span> <span class="identifier">n</span><span class="special">);</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| Converting from values to hooks is generally easy, since most hooks are in |
| practice members or base classes of class data members. The inverse operation |
| is a bit more complicated, but <span class="bold"><strong>Boost.Intrusive</strong></span> |
| offers a bit of help with the function <code class="computeroutput"><a class="link" href="../boost/intrusive/get_parent_from_member_id1019462.html" title="Function template get_parent_from_member">get_parent_from_member</a></code>, |
| which allows easy conversions from the address of a data member to the address |
| of the parent holding that member. Let's see a little example of <code class="computeroutput"><a class="link" href="../boost/intrusive/function_hook.html" title="Struct template function_hook">function_hook</a></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">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">parent_from_member</span><span class="special">.</span><span class="identifier">hpp</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="keyword">struct</span> <span class="identifier">MyClass</span> |
| <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">dummy</span><span class="special">;</span> |
| <span class="comment">//This internal type has a member hook |
| </span> <span class="keyword">struct</span> <span class="identifier">InnerNode</span> |
| <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">dummy</span><span class="special">;</span> |
| <span class="identifier">list_member_hook</span><span class="special"><></span> <span class="identifier">hook</span><span class="special">;</span> |
| <span class="special">}</span> <span class="identifier">inner</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <span class="comment">//This functor converts between MyClass and InnerNode's member hook |
| </span><span class="keyword">struct</span> <span class="identifier">Functor</span> |
| <span class="special">{</span> |
| <span class="comment">//Required types |
| </span> <span class="keyword">typedef</span> <span class="identifier">list_member_hook</span><span class="special"><></span> <span class="identifier">hook_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">hook_type</span><span class="special">*</span> <span class="identifier">hook_ptr</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="keyword">const</span> <span class="identifier">hook_type</span><span class="special">*</span> <span class="identifier">const_hook_ptr</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">MyClass</span> <span class="identifier">value_type</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">value_type</span><span class="special">*</span> <span class="identifier">pointer</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="keyword">const</span> <span class="identifier">value_type</span><span class="special">*</span> <span class="identifier">const_pointer</span><span class="special">;</span> |
| |
| <span class="comment">//Required static functions |
| </span> <span class="keyword">static</span> <span class="identifier">hook_ptr</span> <span class="identifier">to_hook_ptr</span> <span class="special">(</span><span class="identifier">value_type</span> <span class="special">&</span><span class="identifier">value</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="special">&</span><span class="identifier">value</span><span class="special">.</span><span class="identifier">inner</span><span class="special">.</span><span class="identifier">hook</span><span class="special">;</span> <span class="special">}</span> |
| <span class="keyword">static</span> <span class="identifier">const_hook_ptr</span> <span class="identifier">to_hook_ptr</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&</span><span class="identifier">value</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="special">&</span><span class="identifier">value</span><span class="special">.</span><span class="identifier">inner</span><span class="special">.</span><span class="identifier">hook</span><span class="special">;</span> <span class="special">}</span> |
| <span class="keyword">static</span> <span class="identifier">pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">hook_ptr</span> <span class="identifier">n</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">get_parent_from_member</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> |
| <span class="special">(</span><span class="identifier">get_parent_from_member</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">>(</span><span class="identifier">n</span><span class="special">,</span> <span class="special">&</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">::</span><span class="identifier">hook</span><span class="special">)</span> |
| <span class="special">,&</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">inner</span> |
| <span class="special">);</span> |
| <span class="special">}</span> |
| <span class="keyword">static</span> <span class="identifier">const_pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">const_hook_ptr</span> <span class="identifier">n</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">get_parent_from_member</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> |
| <span class="special">(</span><span class="identifier">get_parent_from_member</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">>(</span><span class="identifier">n</span><span class="special">,</span> <span class="special">&</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">::</span><span class="identifier">hook</span><span class="special">)</span> |
| <span class="special">,&</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">inner</span> |
| <span class="special">);</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="comment">//Define a list that will use the hook accessed through the function object |
| </span><span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span> <span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">function_hook</span><span class="special"><</span> <span class="identifier">Functor</span><span class="special">></span> <span class="special">></span> <span class="identifier">List</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="identifier">MyClass</span> <span class="identifier">n</span><span class="special">;</span> |
| <span class="identifier">List</span> <span class="identifier">l</span><span class="special">;</span> |
| <span class="comment">//Insert the node in both lists |
| </span> <span class="identifier">l</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">n</span><span class="special">);</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</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> |
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| <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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