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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="intrusive.scary_iterators"></a><a class="link" href="scary_iterators.html" title="Scary Iterators">Scary Iterators</a> |
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| <p> |
| The paper N2913, titled <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2913.pdf%2c" target="_top">SCARY |
| Iterator Assignment and Initialization</a>, proposed a requirement that |
| a standard container's iterator types have no dependency on any type argument |
| apart from the container's <code class="computeroutput"><span class="identifier">value_type</span></code>, |
| <code class="computeroutput"><span class="identifier">difference_type</span></code>, <code class="computeroutput"><span class="identifier">pointer</span> <span class="identifier">type</span></code>, |
| and <code class="computeroutput"><span class="identifier">const_pointer</span></code> type. In |
| particular, according to the proposal, the types of a standard container's |
| iterators should not depend on the container's <code class="computeroutput"><span class="identifier">key_compare</span></code>, |
| <code class="computeroutput"><span class="identifier">hasher</span></code>, <code class="computeroutput"><span class="identifier">key_equal</span></code>, |
| or <code class="computeroutput"><span class="identifier">allocator</span></code> types. |
| </p> |
| <p> |
| That paper demonstrated that SCARY operations were crucial to the performant |
| implementation of common design patterns using STL components. It showed that |
| implementations that support SCARY operations reduce object code bloat by eliminating |
| redundant specializations of iterator and algorithm templates. |
| </p> |
| <p> |
| <span class="bold"><strong>Boost.Intrusive</strong></span> containers are a bit different |
| from standard containers. In particular, they have no allocator parameter and |
| they can be configured with additional options not present in STL-like containers. |
| Thus <span class="bold"><strong>Boost.Intrusive</strong></span> offers its own <code class="computeroutput"><span class="identifier">SCARY</span> <span class="identifier">iterator</span></code> |
| implementation, where iterator types don't change when the container is configured |
| with an option that does not alter the value <-> node transformation. |
| More concretely, the following options and conditions guarantee that iterator |
| types are unchanged: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> |
| <li class="listitem"> |
| <span class="bold"><strong>All containers</strong></span>: <code class="computeroutput"><span class="identifier">size_type</span><span class="special"><></span></code>, <code class="computeroutput"><span class="identifier">constant_time_size</span><span class="special"><></span></code>, |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong><code class="computeroutput"><span class="identifier">slist</span></code></strong></span>: |
| <code class="computeroutput"><span class="identifier">cache_last</span><span class="special"><></span></code>, |
| <code class="computeroutput"><span class="identifier">linear</span><span class="special"><></span></code>, |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong><code class="computeroutput"><span class="identifier">unordered_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code></strong></span>: |
| <code class="computeroutput"><span class="identifier">hash</span><span class="special"><></span></code>, |
| <code class="computeroutput"><span class="identifier">equal</span><span class="special"><></span></code>, |
| <code class="computeroutput"><span class="identifier">power_2_buckets</span><span class="special"><></span></code>, |
| <code class="computeroutput"><span class="identifier">cache_begin</span><span class="special"><></span></code>. |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong>All tree-like containers</strong></span> (<code class="computeroutput"><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>, |
| <code class="computeroutput"><span class="identifier">avl_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>, <code class="computeroutput"><span class="identifier">sg_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>, |
| <code class="computeroutput"><span class="identifier">bs_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>, <code class="computeroutput"><span class="identifier">splay_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>, |
| <code class="computeroutput"><span class="identifier">treap_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>): <code class="computeroutput"><span class="identifier">compare</span><span class="special"><></span></code>. |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong><code class="computeroutput"><span class="identifier">treap_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code></strong></span>: |
| <code class="computeroutput"><span class="identifier">priority</span><span class="special"><></span></code> |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong><code class="computeroutput"><span class="identifier">bs_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>, |
| <code class="computeroutput"><span class="identifier">sg_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>, <code class="computeroutput"><span class="identifier">treap_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code>, |
| <code class="computeroutput"><span class="identifier">splay_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span></code></strong></span>: They share the same iterator |
| type when configured with the same options. |
| </li> |
| </ul></div> |
| </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<br>Copyright © 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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