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<title>Any Hooks: A single hook for any Intrusive container</title>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="intrusive.any_hooks"></a><a class="link" href="any_hooks.html" title="Any Hooks: A single hook for any Intrusive container">Any Hooks: A single hook for any Intrusive
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<p>
      Sometimes, a class programmer wants to place a class in several intrusive containers
      but no at the same time. In this case, the programmer might decide to insert
      two hooks in the same class.
    </p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">MyClass</span>
   <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">list_base_hook</span><span class="special">&lt;&gt;,</span> <span class="keyword">public</span> <span class="identifier">slist_base_hook</span><span class="special">&lt;&gt;</span> <span class="comment">//...</span>
<span class="special">{};</span>
</pre>
<p>
      However, there is a more size-efficient alternative in <span class="bold"><strong>Boost.Intrusive</strong></span>:
      "any" hooks (<code class="computeroutput"><a class="link" href="../boost/intrusive/any_base_hook.html" title="Class template any_base_hook">any_base_hook</a></code>
      and <code class="computeroutput"><a class="link" href="../boost/intrusive/any_member_hook.html" title="Class template any_member_hook">any_member_hook</a></code>).
      These hooks can be used to store a type in several containers offered by <span class="bold"><strong>Boost.Intrusive</strong></span> minimizing the size of the class.
    </p>
<p>
      These hooks support these options:
    </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          <span class="bold"><strong><code class="computeroutput"><span class="identifier">tag</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Tag</span><span class="special">&gt;</span></code></strong></span>
          (for base hooks only): This argument serves as a tag, so you can derive
          from more than one slist hook. Default: <code class="computeroutput"><span class="identifier">tag</span><span class="special">&lt;</span><span class="identifier">default_tag</span><span class="special">&gt;</span></code>.
        </li>
<li class="listitem">
          <span class="bold"><strong><code class="computeroutput"><span class="identifier">link_mode</span><span class="special">&lt;</span><span class="identifier">link_mode_type</span>
          <span class="identifier">LinkMode</span><span class="special">&gt;</span></code></strong></span>:
          The linking policy. <code class="computeroutput"><span class="identifier">link_mode</span><span class="special">&lt;</span><span class="identifier">auto_unlink</span><span class="special">&gt;</span></code> is <span class="bold"><strong>not</strong></span>
          supported and <code class="computeroutput"><span class="identifier">link_mode</span><span class="special">&lt;</span><span class="identifier">safe_mode</span><span class="special">&gt;</span></code> might offer weaker error detection
          in any hooks than in other hooks. Default: <code class="computeroutput"><span class="identifier">link_mode</span><span class="special">&lt;</span><span class="identifier">safe_link</span><span class="special">&gt;</span></code>.
        </li>
<li class="listitem">
          <span class="bold"><strong><code class="computeroutput"><span class="identifier">void_pointer</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">VoidPointer</span><span class="special">&gt;</span></code></strong></span>:
          The pointer type to be used internally in the hook and propagated to the
          container. Default: <code class="computeroutput"><span class="identifier">void_pointer</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">*&gt;</span></code>.
        </li>
</ul></div>
<p>
      <code class="computeroutput"><span class="identifier">auto_unlink</span></code> can't be supported
      because the hook does not know in which type of container might be currently
      inserted. Additionally, these hooks don't support <code class="computeroutput"><span class="identifier">unlink</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">swap_nodes</span><span class="special">()</span></code> operations for the same reason.
    </p>
<p>
      Here is an example that creates a class with two any hooks, and uses one to
      insert the class in a <code class="computeroutput">slist</code> and the other
      one in a <code class="computeroutput">list</code>.
    </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">any_hook</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">slist</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</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">class</span> <span class="identifier">MyClass</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">any_base_hook</span><span class="special">&lt;&gt;</span> <span class="comment">//Base hook</span>
<span class="special">{</span>
   <span class="keyword">int</span> <span class="identifier">int_</span><span class="special">;</span>

   <span class="keyword">public</span><span class="special">:</span>
   <span class="identifier">any_member_hook</span><span class="special">&lt;&gt;</span> <span class="identifier">member_hook_</span><span class="special">;</span>  <span class="comment">//Member hook</span>

   <span class="identifier">MyClass</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="special">:</span> <span class="identifier">int_</span><span class="special">(</span><span class="identifier">i</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="comment">//Define a base hook option that converts any_base_hook to a slist hook</span>
   <span class="keyword">typedef</span> <span class="identifier">any_to_slist_hook</span> <span class="special">&lt;</span> <span class="identifier">base_hook</span><span class="special">&lt;</span> <span class="identifier">any_base_hook</span><span class="special">&lt;&gt;</span> <span class="special">&gt;</span> <span class="special">&gt;</span>     <span class="identifier">BaseSlistOption</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">slist</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">BaseSlistOption</span><span class="special">&gt;</span>                        <span class="identifier">BaseSList</span><span class="special">;</span>

   <span class="comment">//Define a member hook option that converts any_member_hook to a list hook</span>
   <span class="keyword">typedef</span> <span class="identifier">any_to_list_hook</span><span class="special">&lt;</span> <span class="identifier">member_hook</span>
         <span class="special">&lt;</span> <span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">any_member_hook</span><span class="special">&lt;&gt;,</span> <span class="special">&amp;</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">member_hook_</span><span class="special">&gt;</span> <span class="special">&gt;</span>  <span class="identifier">MemberListOption</span><span class="special">;</span>
   <span class="keyword">typedef</span> <span class="identifier">list</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">MemberListOption</span><span class="special">&gt;</span>                        <span class="identifier">MemberList</span><span class="special">;</span>

   <span class="comment">//Create several MyClass objects, each one with a different value</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;</span> <span class="identifier">values</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">&lt;</span> <span class="number">100</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">){</span> <span class="identifier">values</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">MyClass</span><span class="special">(</span><span class="identifier">i</span><span class="special">));</span> <span class="special">}</span>

   <span class="identifier">BaseSList</span> <span class="identifier">base_slist</span><span class="special">;</span>   <span class="identifier">MemberList</span> <span class="identifier">member_list</span><span class="special">;</span>

   <span class="comment">//Now insert them in reverse order in the slist and in order in the list</span>
   <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;::</span><span class="identifier">iterator</span> <span class="identifier">it</span><span class="special">(</span><span class="identifier">values</span><span class="special">.</span><span class="identifier">begin</span><span class="special">()),</span> <span class="identifier">itend</span><span class="special">(</span><span class="identifier">values</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> <span class="identifier">it</span> <span class="special">!=</span> <span class="identifier">itend</span><span class="special">;</span> <span class="special">++</span><span class="identifier">it</span><span class="special">)</span>
      <span class="identifier">base_slist</span><span class="special">.</span><span class="identifier">push_front</span><span class="special">(*</span><span class="identifier">it</span><span class="special">),</span> <span class="identifier">member_list</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(*</span><span class="identifier">it</span><span class="special">);</span>

   <span class="comment">//Now test lists</span>
   <span class="identifier">BaseSList</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">bit</span><span class="special">(</span><span class="identifier">base_slist</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
   <span class="identifier">MemberList</span><span class="special">::</span><span class="identifier">reverse_iterator</span> <span class="identifier">mrit</span><span class="special">(</span><span class="identifier">member_list</span><span class="special">.</span><span class="identifier">rbegin</span><span class="special">());</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">MyClass</span><span class="special">&gt;::</span><span class="identifier">reverse_iterator</span> <span class="identifier">rit</span><span class="special">(</span><span class="identifier">values</span><span class="special">.</span><span class="identifier">rbegin</span><span class="special">()),</span> <span class="identifier">ritend</span><span class="special">(</span><span class="identifier">values</span><span class="special">.</span><span class="identifier">rend</span><span class="special">());</span>

   <span class="comment">//Test the objects inserted in the base hook list</span>
   <span class="keyword">for</span><span class="special">(;</span> <span class="identifier">rit</span> <span class="special">!=</span> <span class="identifier">ritend</span><span class="special">;</span> <span class="special">++</span><span class="identifier">rit</span><span class="special">,</span> <span class="special">++</span><span class="identifier">bit</span><span class="special">,</span> <span class="special">++</span><span class="identifier">mrit</span><span class="special">)</span>
      <span class="keyword">if</span><span class="special">(&amp;*</span><span class="identifier">bit</span> <span class="special">!=</span> <span class="special">&amp;*</span><span class="identifier">rit</span> <span class="special">||</span> <span class="special">&amp;*</span><span class="identifier">mrit</span> <span class="special">!=</span> <span class="special">&amp;*</span><span class="identifier">rit</span><span class="special">)</span>  <span class="keyword">return</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 &#169; 2005 Olaf Krzikalla<br>Copyright &#169; 2006-2013 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>
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