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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="intrusive.obtaining_same_type_reducing_space"></a><a class="link" href="obtaining_same_type_reducing_space.html" title="Obtaining the same types and reducing symbol length">Obtaining |
| the same types and reducing symbol length</a> |
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| <p> |
| The flexible option specification mechanism used by <span class="bold"><strong>Boost.Intrusive</strong></span> |
| for hooks and containers has a couple of downsides: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| If a user specifies the same options in different order or specifies some |
| options and leaves the rest as defaults, the type of the created container/hook |
| will be different. Sometimes this is annoying, because two programmers |
| specifying the same options might end up with incompatible types. For example, |
| the following two lists, although using the same options, do not have the |
| same type: |
| </li></ul></div> |
| <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="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">//Explicitly specify constant-time size and size type |
| </span><span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">constant_time_size</span><span class="special"><</span><span class="keyword">true</span><span class="special">>,</span> <span class="identifier">size_type</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">List1</span><span class="special">;</span> |
| |
| <span class="comment">//Implicitly specify constant-time size and size type |
| </span><span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">List2</span><span class="special">;</span> |
| </pre> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| Option specifiers lead to long template symbols for classes and functions. |
| Option specifiers themselves are verbose and without variadic templates, |
| several default template parameters are assigned for non-specified options. |
| Object and debugging information files can grow and compilation times may |
| suffer if long names are produced. |
| </li></ul></div> |
| <p> |
| To solve these issues <span class="bold"><strong>Boost.Intrusive</strong></span> offers |
| some helper metafunctions that reduce symbol lengths and create the same type |
| if the same options (either explicitly or implicitly) are used. These also |
| improve compilation times. All containers and hooks have their respective |
| <code class="computeroutput"><span class="identifier">make_xxx</span></code> versions. The previously |
| shown example can be rewritten like this to obtain the same list type: |
| </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="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="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="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">//Explicitly specify constant-time size and size type |
| </span> <span class="keyword">typedef</span> <span class="identifier">make_list</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">constant_time_size</span><span class="special"><</span><span class="keyword">true</span><span class="special">>,</span> <span class="identifier">size_type</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">List1</span><span class="special">;</span> |
| |
| <span class="comment">//Implicitly specify constant-time size and size type |
| </span> <span class="keyword">typedef</span> <span class="identifier">make_list</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">List2</span><span class="special">;</span> |
| </pre> |
| <p> |
| Produced symbol lengths and compilation times will usually be shorter and object/debug |
| files smaller. If you are concerned with file sizes and compilation times, |
| this option is your best choice. |
| </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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