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<h1><img src="../../../../boost.png" alt="Boost logo" align=
"middle" width="277" height="86">Boost.Flyweight
Holders reference</h1>

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<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&lt;S&gt;::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&lt;S'&gt;</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>&lt;</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>&gt;</span>
<span class=keyword>struct</span> <span class=identifier>is_holder</span><span class=special>;</span>

<span class=keyword>template</span><span class=special>&lt;</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>&gt;</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&lt;T&gt;::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&lt;T&gt;</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>&lt;</span><span class=keyword>typename</span> <span class=identifier>C</span><span class=special>&gt;</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&lt;C&gt;</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>&lt;</span><span class=keyword>typename</span> <span class=identifier>C</span><span class=special>&gt;</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&lt;C&gt;</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>

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<br>

<p>Revised August 11th 2008</p>

<p>&copy; Copyright 2006-2008 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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