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<title>Boost.Flyweight Documentation - Holders reference</title>
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<h1><img src="../../../../boost.png" alt="Boost logo" align=
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"middle" width="277" height="86">Boost.Flyweight
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Holders reference</h1>
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Factories
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Boost.Flyweight reference
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Locking policies
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</a></div><br clear="all" style="clear: all;">
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<hr>
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<h2>Contents</h2>
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<ul>
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<li><a href="#holder">Holders and holder specifiers</a></li>
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<li><a href="#holder_tag_synopsis">Header
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<code>"boost/flyweight/holder_tag.hpp"</code> synopsis</a>
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<ul>
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<li><a href="#is_holder">Class template <code>is_holder</code></a></li>
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<li><a href="#holder_construct">Class template <code>holder</code></a></li>
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</ul>
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</li>
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<li><a href="#static_holder_fwd_synopsis">Header
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<code>"boost/flyweight/static_holder_fwd.hpp"</code> synopsis</a>
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</li>
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<li><a href="#static_holder_synopsis">Header
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<code>"boost/flyweight/static_holder.hpp"</code> synopsis</a>
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<ul>
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<li><a href="#static_holder_class">Class template <code>static_holder_class</code></a></li>
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<li><a href="#static_holder">Class <code>static_holder</code></a></li>
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</ul>
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</li>
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<li><a href="#intermodule_holder_fwd_synopsis">Header
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<code>"boost/flyweight/intermodule_holder_fwd.hpp"</code> synopsis</a>
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</li>
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<li><a href="#intermodule_holder_synopsis">Header
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<code>"boost/flyweight/intermodule_holder.hpp"</code> synopsis</a>
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<ul>
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<li><a href="#intermodule_holder_class">Class template <code>intermodule_holder_class</code></a></li>
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<li><a href="#intermodule_holder">Class <code>intermodule_holder</code></a></li>
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</ul>
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</li>
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</ul>
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<h2><a name="holder">Holders and holder specifiers</a></h2>
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<p>
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Given a type <code>C</code>, a type <code>Holder</code> is said to be a <i>holder
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of <code>C</code></i> if the expression <code>Holder::get()</code> returns
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a reference to a default initialized <code>C</code> object unique to
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<code>Holder</code>. No invocation of <code>Holder::get()</code>, except possibly
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the first one in the program, does throw.
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<a href="flyweight.html#flyweight"><code>flyweight</code></a>
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privately uses a holder to instantiate a <a href="factories.html#factory">factory</a>
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and some additional data (like a <a href="locking.html#preliminary">mutex</a> for
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internal synchronization) unique to each instantiation type of the class template.
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</p>
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<p>
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A type <code>S</code> is a <i>holder specifier</i> if:
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<ol>
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<li>One of the following conditions is satisfied:
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<ol type="a">
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<li><a href="#is_holder"><code>is_holder<S>::type</code></a> is
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<a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::true_</code></a>,</li>
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<li><code>S</code> is of the form <a href="#holder_construct"><code>holder<S'></code></a>.</li>
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</ol>
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</li>
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<li><code>S</code>, or <code>S'</code> if (b) applies, is an
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<a href="../../../mpl/doc/refmanual/lambda-expression.html"><code>MPL Lambda
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Expression</code></a> such that invoking it with type <code>C</code> resolves to
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a holder of <code>C</code>.
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</li>
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</ol>
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</p>
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<h2><a name="holder_tag_synopsis">Header
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<a href="../../../../boost/flyweight/holder_tag.hpp"><code>"boost/flyweight/holder_tag.hpp"</code></a> synopsis</a></h2>
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<blockquote><pre>
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<span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
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<span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
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<span class=keyword>struct</span> <span class=identifier>holder_marker</span><span class=special>;</span>
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<span class=keyword>template</span><span class=special><</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>></span>
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<span class=keyword>struct</span> <span class=identifier>is_holder</span><span class=special>;</span>
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<span class=keyword>template</span><span class=special><</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>></span>
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<span class=keyword>struct</span> <span class=identifier>holder</span><span class=special>;</span>
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<span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
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<span class=special>}</span> <span class=comment>// namespace boost</span>
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</pre></blockquote>
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<h3><a name="is_holder">Class template <code>is_holder</code></a></h3>
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<p>
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Unless specialized by the user, <code>is_holder<T>::type</code> is
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<a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::true_</code></a>
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if <code>T</code> is derived from <code>holder_marker</code>, and it is
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<a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::false_</code></a>
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otherwise.
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</p>
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<h3><a name="holder_construct">Class template <code>holder</code></a></h3>
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<p>
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<code>holder<T></code> is a syntactic construct meant to indicate
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that <code>T</code> is a holder specifier without resorting to the
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mechanisms provided by the <code>is_holder</code> class template.
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</p>
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<h2><a name="static_holder_fwd_synopsis">Header
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<a href="../../../../boost/flyweight/static_holder_fwd.hpp"><code>"boost/flyweight/static_holder_fwd.hpp"</code></a> synopsis</a></h2>
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<blockquote><pre>
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<span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
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<span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
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<span class=keyword>template</span><span class=special><</span><span class=keyword>typename</span> <span class=identifier>C</span><span class=special>></span>
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<span class=keyword>struct</span> <span class=identifier>static_holder_class</span><span class=special>;</span>
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<span class=keyword>struct</span> <span class=identifier>static_holder</span><span class=special>;</span>
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<span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
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<span class=special>}</span> <span class=comment>// namespace boost</span>
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</pre></blockquote>
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<p>
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<code>static_holder_fwd.hpp</code> forward declares
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<a href="#static_holder_class"><code>static_holder_class</code></a>
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and <a href="#static_holder"><code>static_holder</code></a>.
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</p>
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<h2><a name="static_holder_synopsis">Header
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<a href="../../../../boost/flyweight/static_holder.hpp"><code>"boost/flyweight/static_holder.hpp"</code></a> synopsis</a></h2>
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<h3><a name="static_holder_class">Class template <code>static_holder_class</code></a></h3>
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<p>
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<code>static_holder_class<C></code> keeps its unique instance of <code>C</code> as a
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local static object.
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</p>
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<h3><a name="static_holder">Class <code>static_holder</code></a></h3>
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<p>
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<a href="#holder"><code>Holder Specifier</code></a> for <a href="#static_holder_class"><code>static_holder_class</code></a>.
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</p>
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<h2><a name="intermodule_holder_fwd_synopsis">Header
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<a href="../../../../boost/flyweight/intermodule_holder_fwd.hpp"><code>"boost/flyweight/intermodule_holder_fwd.hpp"</code></a> synopsis</a></h2>
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<blockquote><pre>
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<span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
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<span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
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<span class=keyword>template</span><span class=special><</span><span class=keyword>typename</span> <span class=identifier>C</span><span class=special>></span>
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<span class=keyword>struct</span> <span class=identifier>intermodule_holder_class</span><span class=special>;</span>
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<span class=keyword>struct</span> <span class=identifier>intermodule_holder</span><span class=special>;</span>
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<span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
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<span class=special>}</span> <span class=comment>// namespace boost</span>
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</pre></blockquote>
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<p>
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<code>intermodule_holder_fwd.hpp</code> forward declares
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<a href="#intermodule_holder_class"><code>intermodule_holder_class</code></a>
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and <a href="#intermodule_holder"><code>intermodule_holder</code></a>.
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</p>
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<h2><a name="intermodule_holder_synopsis">Header
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<a href="../../../../boost/flyweight/intermodule_holder.hpp"><code>"boost/flyweight/intermodule_holder.hpp"</code></a> synopsis</a></h2>
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<h3><a name="intermodule_holder_class">Class template <code>intermodule_holder_class</code></a></h3>
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<p>
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<code>intermodule_holder_class<C></code> maintains a <code>C</code>
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instance which is unique even across different dynamically linked modules of
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the program using this same type. In general, this guarantee is not provided by
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<a href="#static_holder_class"><code>static_holder_class</code></a>, as most
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C++ implementations are not able to merge duplicates of static variables stored
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in different dynamic modules of a program.
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</p>
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<h3><a name="intermodule_holder">Class <code>intermodule_holder</code></a></h3>
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<p>
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<a href="#holder"><code>Holder Specifier</code></a> for <a href="#intermodule_holder_class"><code>intermodule_holder_class</code></a>.
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</p>
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<hr>
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<div class="prev_link"><a href="factories.html"><img src="../prev.gif" alt="factories" border="0"><br>
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Factories
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</a></div>
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<div class="up_link"><a href="index.html"><img src="../up.gif" alt="Boost.Flyweight reference" border="0"><br>
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Boost.Flyweight reference
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</a></div>
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<div class="next_link"><a href="locking.html"><img src="../next.gif" alt="locking policies" border="0"><br>
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Locking policies
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</a></div><br clear="all" style="clear: all;">
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<br>
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<p>Revised August 11th 2008</p>
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<p>© Copyright 2006-2008 Joaquín M López Muñoz.
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Distributed under the Boost Software
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License, Version 1.0. (See accompanying file <a href="../../../../LICENSE_1_0.txt">
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LICENSE_1_0.txt</a> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">
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http://www.boost.org/LICENSE_1_0.txt</a>)
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</p>
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