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<title>Boost.Flyweight Documentation - Future work</title>
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<h1><img src="../../../boost.png" alt="Boost logo" align=
"middle" width="277" height="86">Boost.Flyweight Future work</h1>

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<p>
New functionalities can be included into future releases of Boost.Flyweight
to meet the demands of users and to leverage upcoming C++ features
and new Boost libraries. The following is a list of candidate additions.
</p>

<h2>Contents</h2>

<ul>
  <li><a href="#instrospection">Introspection API</a></li>
  <li><a href="#rw_lock">Read/write locking policy</a></li>
  <li><a href="#new_boost_libs">Integration with new Boost libraries</a></li>
</ul>

<h2><a name="instrospection">Introspection API</a></h2>

<p>
Currently there is no way to access the internal components of a
<code>flyweight</code> instantiation (factory, holder, etc.) or even
to know the types of these components. With such an API it would be
possible to instrument and monitor the usage of Boost.Flyweight like in
the following example:
</p>

<blockquote><pre>
<span class=keyword>typedef</span> <span class=identifier>flyweight</span><span class=special>&lt;</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&gt;</span> <span class=identifier>fw_type</span><span class=special>;</span>
<span class=special>...</span>
<span class=identifier>std</span><span class=special>::</span><span class=identifier>cout</span><span class=special>&lt;&lt;</span><span class=string>&quot;factory used:  &quot;</span><span class=special>&lt;&lt;</span><span class=keyword>typeid</span><span class=special>(</span><span class=identifier>fw_type</span><span class=special>::</span><span class=identifier>factory_type</span><span class=special>).</span><span class=identifier>name</span><span class=special>()&lt;&lt;</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>endl</span><span class=special>;</span>
<span class=identifier>std</span><span class=special>::</span><span class=identifier>cout</span><span class=special>&lt;&lt;</span><span class=string>&quot;values stored: &quot;</span><span class=special>&lt;&lt;</span><span class=identifier>fw_type</span><span class=special>::</span><span class=identifier>factory</span><span class=special>().</span><span class=identifier>size</span><span class=special>()&lt;&lt;</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>endl</span><span class=special>;</span>
</pre></blockquote>

<h2><a name="rw_lock">Read/write locking policy</a></h2>

<p>
The nature of the flyweight pattern implies that most accesses
to the internal flyweight factory do not cause new insertions and can
thus be considered read-only. This hints at the convenience of using
a locking policy based on read/write locks such as those provided by
<a href="../../../doc/html/thread/synchronization.html#thread.synchronization.mutex_concepts.shared_lockable">Boost.Thread</a>.
Implementing a locking policy will also require extending the
<a href="reference/factories.html#factory"><code>Factory</code></a> concept
to allow for pure lookup operations. Tim Blechmann has provided a
preliminary <a href="http://lists.boost.org/Archives/boost/2008/07/139414.php">implementation</a>
of this idea. Before committing to this library extension it is
necessary to do a profiling study to determine whether read/write
locking actually improves performance.
</p>

<h2><a name="new_boost_libs">Integration with new Boost libraries</a></h2>

<p>
Recently accepted Boost libraries like
<a href="http://lists.boost.org/boost-announce/2007/12/0149.php">Boost.Functional/Forward</a>
and <a href="http://lists.boost.org/boost-announce/2007/12/0157.php">Boost.Functional/Factory</a>
might be used in the future to replace some internal machinery of
Boost.Flyweight.
</p>

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<p>Revised April 24th 2019</p>

<p>&copy; Copyright 2006-2019 Joaqu&iacute;n M L&oacute;pez Mu&ntilde;oz.
Distributed under the Boost Software 
License, Version 1.0. (See accompanying file <a href="../../../LICENSE_1_0.txt">
LICENSE_1_0.txt</a> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">
http://www.boost.org/LICENSE_1_0.txt</a>)
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