ceph/src/boost/libs/flyweight/doc/future_work.html

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  15 <h1><img src="../../../boost.png" alt="Boost logo" align=
  16 "middle" width="277" height="86">Boost.Flyweight Future work</h1>
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  31 <p>
  32 New functionalities can be included into future releases of Boost.Flyweight
  33 to meet the demands of users and to leverage upcoming C++0x features
  34 and new Boost libraries. The following is a list of candidate additions.
  35 </p>
  36
  37 <h2>Contents</h2>
  38
  39 <ul>
  40   <li><a href="#instrospection">Introspection API</a></li>
  41   <li><a href="#perfect_fwd">Perfect forwarding</a></li>
  42   <li><a href="#rw_lock">Read/write locking policy</a></li>
  43   <li><a href="#new_boost_libs">Integration with new Boost libraries</a></li>
  44 </ul>
  45
  46 <h2><a name="instrospection">Introspection API</a></h2>
  47
  48 <p>
  49 Currently there is no way to access the internal components of a
  50 <code>flyweight</code> instantiation (factory, holder, etc.) or even
  51 to know the types of these components. With such an API it would be
  52 possible to instrument and monitor the usage of Boost.Flyweight like in
  53 the following example:
  54 </p>
  55
  56 <blockquote><pre>
  57 <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>
  58 <span class=special>...</span>
  59 <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>
  60 <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>
  61 </pre></blockquote>
  62
  63 <h2><a name="perfect_fwd">Perfect forwarding</a></h2>
  64
  65 <p>
  66 When constructing a <code>flyweight&lt;T&gt; object</code>, some spurious copies
  67 of objects of type <code>T</code> are incurred in the process of moving the value
  68 into the internal factory. So-called <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2027.html#Perfect_Forwarding"><i>perfect
  69 forwarding</i></a>, i.e. performing the move without generating temporary
  70 copies, will be solved in an optimum manner by a new
  71 type of <i>rvalue references</i> to be included in the next revision of the
  72 C++ standard. Boost.Flyweight will take advantage of this feature as
  73 compilers begin to provide it.
  74 </p>
  75
  76 <h2><a name="rw_lock">Read/write locking policy</a></h2>
  77
  78 <p>
  79 The nature of the flyweight pattern implies that most accesses
  80 to the internal flyweight factory do not cause new insertions and can
  81 thus be considered read-only. This hints at the convenience of using
  82 a locking policy based on read/write locks such as those provided by
  83 <a href="../../../doc/html/thread/synchronization.html#thread.synchronization.mutex_concepts.shared_lockable">Boost.Thread</a>.
  84 Implementing a locking policy will also require extending the
  85 <a href="reference/factories.html#factory"><code>Factory</code></a> concept
  86 to allow for pure lookup operations. Tim Blechmann has provided a
  87 preliminary <a href="http://lists.boost.org/Archives/boost/2008/07/139414.php">implementation</a>
  88 of this idea. Before committing to this library extension it is
  89 necessary to do a profiling study to determine whether read/write
  90 locking actually improves performance.
  91 </p>
  92
  93 <h2><a name="new_boost_libs">Integration with new Boost libraries</a></h2>
  94
  95 <p>
  96 Recently accepted Boost libraries like
  97 <a href="http://lists.boost.org/boost-announce/2007/12/0149.php">Boost.Functional/Forward</a>
  98 and <a href="http://lists.boost.org/boost-announce/2007/12/0157.php">Boost.Functional/Factory</a>
  99 might be used in the future to replace some internal machinery of
 100 Boost.Flyweight.
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 116 <br>
 117
 118 <p>Revised September 1st 2008</p>
 119
 120 <p>&copy; Copyright 2006-2008 Joaqu&iacute;n M L&oacute;pez Mu&ntilde;oz.
 121 Distributed under the Boost Software
 122 License, Version 1.0. (See accompanying file <a href="../../../LICENSE_1_0.txt">
 123 LICENSE_1_0.txt</a> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">
 124 http://www.boost.org/LICENSE_1_0.txt</a>)
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