<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0.1 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Boost.Flyweight Documentation - Tracking policies reference</title>
<link rel="stylesheet" href="../style.css" type="text/css">
<link rel="start" href="../index.html">
<link rel="prev" href="locking.html">
<link rel="up" href="index.html">
<link rel="next" href="../performance.html">
</head>
<body>
<h1><img src="../../../../boost.png" alt="Boost logo" align=
"middle" width="277" height="86">Boost.Flyweight
Tracking policies reference</h1>
<div class="prev_link"><a href="locking.html"><img src="../prev.gif" alt="locking policies" border="0"><br>
Locking policies
</a></div>
<div class="up_link"><a href="index.html"><img src="../up.gif" alt="Boost.Flyweight reference" border="0"><br>
Boost.Flyweight reference
</a></div>
<div class="next_link"><a href="../performance.html"><img src="../next.gif" alt="performance" border="0"><br>
Performance
</a></div><br clear="all" style="clear: all;">
<hr>
<h2>Contents</h2>
<ul>
<li><a href="#preliminary">Preliminary concepts</a></li>
<li><a href="#tracking">Tracking policies</a></li>
<li><a href="#tracking_tag_synopsis">Header
<code>"boost/flyweight/tracking_tag.hpp"</code> synopsis</a>
<ul>
<li><a href="#is_tracking">Class template <code>is_tracking</code></a></li>
<li><a href="#tracking_construct">Class template <code>tracking</code></a></li>
</ul>
</li>
<li><a href="#refcounted_fwd_synopsis">Header
<code>"boost/flyweight/refcounted_fwd.hpp"</code> synopsis</a>
</li>
<li><a href="#refcounted_synopsis">Header
<code>"boost/flyweight/refcounted.hpp"</code> synopsis</a>
<ul>
<li><a href="#refcounted">Class <code>refcounted</code></a></li>
</ul>
</li>
<li><a href="#no_tracking_fwd_synopsis">Header
<code>"boost/flyweight/no_tracking_fwd.hpp"</code> synopsis</a>
</li>
<li><a href="#no_tracking_synopsis">Header
<code>"boost/flyweight/no_tracking.hpp"</code> synopsis</a>
<ul>
<li><a href="#no_tracking">Class <code>no_tracking</code></a></li>
</ul>
</li>
</ul>
<h2><a name="preliminary">Preliminary concepts</a></h2>
<p>
A <i>tracking policy helper</i> provides access to some of the functionality
of a <a href="factories.html#factory">factory</a> so as to be used
in the implementation of an associated <a href="#tracking"><code>Tracking Policy</code></a>.
In the following table, <code>TrackingHelper</code> is a tracking policy
helper associated to a <a href="factories.html#factory">factory</a> type
<code>Factory</code> of elements of type <code>Entry</code>, <code>h</code>
is a value of
<code>Factory::handle_type</code> associated to a <code>Factory</code> <code>f</code>
and <code>check</code> is a value of
a <a href="http://www.sgi.com/tech/stl/Predicate.html"><code>Predicate</code></a>
type <code>Checker</code> with argument of type <code>Factory::handle_type</code>.
</p>
<p align="center">
<table cellspacing="0">
<caption><b>Tracking Policy Helper requirements.</b></caption>
<tr>
<th align="center">expression</th>
<th align="center">return type</th>
<th align="center">assertion/note<br>pre/post-condition</th>
</tr>
<tr>
<td><code>TrackingHelper::entry(h);</code></td>
<td><code>const Entry&</code></td>
<td>Returns <code>f.entry(h)</code>.</td>
</tr>
<tr class="odd_tr">
<td><code>TrackingHelper::erase(h,check);</code></td>
<td><code>void</code></td>
<td>If <code>check(h)</code>, invokes <code>f.erase(h)</code>.</td>
</tr>
</table>
</p>
<p>
The execution of <code>TrackingHelper::erase</code> (including the
invocation of <code>check(h)</code>) is done in a
synchronized manner so as to prevent any other thread of execution from
simultaneously accessing the factory's insertion or deletion facilities.
</p>
<h2><a name="tracking">Tracking policies</a></h2>
<p>
A <i>tracking policy</i> defines the strategy to be followed by a
<a href="flyweight.html#flyweight"><code>flyweight</code></a> instantiation when
all the flyweight objects associated to a given value are destroyed.
The tracking policy contributes some type information necessary for the
definition of the <code>flyweight</code> internal
<a href="factories.html#factory">factory</a>.
</p>
<p>
A type <code>Tracking</code> is a tracking policy if:
<ul>
<li>One of the following conditions is satisfied:
<ol type="a">
<li><a href="#is_tracking"><code>is_tracking<Tracking>::type</code></a> is
<a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::true_</code></a>,</li>
<li><code>Tracking</code> is of the form
<a href="#tracking_construct"><code>tracking<Tracking'></code></a>.</li>
</ol>
</li>
<li>The expression <code>Tracking::entry_type</code> (or
<code>Tracking'::entry_type</code> if (b) applies) is an
<a href="../../../mpl/doc/refmanual/lambda-expression.html"><code>MPL Lambda
Expression</code></a> that resolves, when invoked with different types
(<code>Value</code>,<code>Key</code>) such that <code>Value</code> is
<a href="http://www.sgi.com/tech/stl/Assignable.html"><code>Assignable</code></a>
and implicitly convertible to <code>const Key&</code>, to an
<a href="http://www.sgi.com/tech/stl/Assignable.html"><code>Assignable</code></a>
type <code>Entry</code> implicitly convertible to both <code>const Value&</code>
and <code>const Key&</code>.
</li>
<li>The expression <code>Tracking::handle_type</code> (or
<code>Tracking'::handle_type</code> if (b) applies) is an
<a href="../../../mpl/doc/refmanual/lambda-expression.html"><code>MPL Lambda
Expression</code></a>; this expression, when invoked with types
(<code>InternalHandle</code>,<a href="#preliminary"><code>TrackingHelper</code></a>),
with <code>InternalHandle</code> being
<a href="http://www.sgi.com/tech/stl/Assignable.html"><code>Assignable</code></a>
and providing the nothrow guarantee for copy and assignment,
resolves to an
<a href="http://www.sgi.com/tech/stl/Assignable.html"><code>Assignable</code></a>
type <code>Handle</code> which also provides the nothrow guarantee for
copy and assignment and is constructible from and implicitly
convertible to <code>InternalHandle</code>.
<code>TrackingHelper</code> is an incomplete type at the time of
invocation of <code>Tracking::handle_type</code>.
</li>
</ul>
<code>Tracking::handle_type</code> is parameterized by a helper that provides
access to some of the functionality of the factory associated to the
tracking policy. This factory's associated entry and handle types are the types
<code>Entry</code> and <code>Handle</code> defined above, respectively.
</p>
<h2><a name="tracking_tag_synopsis">Header
<a href="../../../../boost/flyweight/tracking_tag.hpp"><code>"boost/flyweight/tracking_tag.hpp"</code></a> synopsis</a></h2>
<blockquote><pre>
<span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
<span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
<span class=keyword>struct</span> <span class=identifier>tracking_marker</span><span class=special>;</span>
<span class=keyword>template</span><span class=special><</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>></span>
<span class=keyword>struct</span> <span class=identifier>is_tracking</span>
<span class=keyword>template</span><span class=special><</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>></span>
<span class=keyword>struct</span> <span class=identifier>tracking</span><span class=special>;</span>
<span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
<span class=special>}</span> <span class=comment>// namespace boost</span>
</pre></blockquote>
<h3><a name="is_tracking">Class template <code>is_tracking</code></a></h3>
<p>
Unless specialized by the user, <code>is_tracking<T>::type</code> is
<a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::true_</code></a>
if <code>T</code> is derived from <code>tracking_marker</code>, and it is
<a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::false_</code></a>
otherwise.
</p>
<h3><a name="tracking_construct">Class template <code>tracking</code></a></h3>
<p>
<code>tracking<T></code> is a syntactic construct meant to indicate
that <code>T</code> is a tracking policy without resorting to the
mechanisms provided by the <code>is_tracking</code> class template.
</p>
<h2><a name="refcounted_fwd_synopsis">Header
<a href="../../../../boost/flyweight/refcounted_fwd.hpp"><code>"boost/flyweight/refcounted_fwd.hpp"</code></a> synopsis</a></h2>
<blockquote><pre>
<span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
<span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
<span class=keyword>struct</span> <span class=identifier>refcounted</span><span class=special>;</span>
<span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
<span class=special>}</span> <span class=comment>// namespace boost</span>
</pre></blockquote>
<p>
<code>refcounted_fwd.hpp</code> forward declares the class
<a href="#refcounted"><code>refcounted</code></a>.
</p>
<h2><a name="refcounted_synopsis">Header
<a href="../../../../boost/flyweight/refcounted.hpp"><code>"boost/flyweight/refcounted.hpp"</code></a> synopsis</a></h2>
<h3><a name="refcounted">Class <code>refcounted</code></a></h3>
<p>
<a href="#tracking"><code>Tracking Policy</code></a> providing
<a href="flyweight.html#flyweight"><code>flyweight</code></a>
instantiations with reference counting semantics: when all the flyweight objects
associated to a given value are destroyed, the corresponding entry is
erased from <code>flyweight</code>'s internal
<a href="factories.html#factory">factory</a>.
</p>
<h2><a name="no_tracking_fwd_synopsis">Header
<a href="../../../../boost/flyweight/no_tracking_fwd.hpp"><code>"boost/flyweight/no_tracking_fwd.hpp"</code></a> synopsis</a></h2>
<blockquote><pre>
<span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
<span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
<span class=keyword>struct</span> <span class=identifier>no_tracking</span><span class=special>;</span>
<span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
<span class=special>}</span> <span class=comment>// namespace boost</span>
</pre></blockquote>
<p>
<code>no_tracking_fwd.hpp</code> forward declares the class
<a href="#no_tracking"><code>no_tracking</code></a>.
</p>
<h2><a name="no_tracking_synopsis">Header
<a href="../../../../boost/flyweight/no_tracking.hpp"><code>"boost/flyweight/no_tracking.hpp"</code></a> synopsis</a></h2>
<h3><a name="no_tracking">Class <code>no_tracking</code></a></h3>
<p>
Null <a href="#tracking"><code>Tracking Policy</code></a>: elements inserted
into <code>flyweight</code>'s internal <a href="factories.html#factory">factory</a>
are not erased until program termination.
</p>
<hr>
<div class="prev_link"><a href="locking.html"><img src="../prev.gif" alt="locking policies" border="0"><br>
Locking policies
</a></div>
<div class="up_link"><a href="index.html"><img src="../up.gif" alt="Boost.Flyweight reference" border="0"><br>
Boost.Flyweight reference
</a></div>
<div class="next_link"><a href="../performance.html"><img src="../next.gif" alt="performance" border="0"><br>
Performance
</a></div><br clear="all" style="clear: all;">
<br>
<p>Revised August 18th 2008</p>
<p>© Copyright 2006-2008 Joaquín M López Muñoz.
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>)
</p>
</body>
</html>
