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