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- <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
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- Boost.Flyweight reference
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- <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="https://boost.org/sgi/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="https://boost.org/sgi/stl/Assignable.html"><code>Assignable</code></a>
- and implicitly convertible to <code>const Key&</code>, to an
- <a href="https://boost.org/sgi/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="https://boost.org/sgi/stl/Assignable.html"><code>Assignable</code></a>
- and providing the nothrow guarantee for copy and assignment,
- resolves to an
- <a href="https://boost.org/sgi/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
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- Boost.Flyweight reference
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- </a></div><br clear="all" style="clear: all;">
- <br>
- <p>Revised April 24th 2019</p>
- <p>© Copyright 2006-2019 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>)
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