ceph/src/boost/libs/flyweight/doc/reference/holders.html

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  15 <h1><img src="../../../../boost.png" alt="Boost logo" align=
  16 "middle" width="277" height="86">Boost.Flyweight
  17 Holders reference</h1>
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  31 <h2>Contents</h2>
  32
  33 <ul>
  34   <li><a href="#holder">Holders and holder specifiers</a></li>
  35   <li><a href="#holder_tag_synopsis">Header
  36     <code>"boost/flyweight/holder_tag.hpp"</code> synopsis</a>
  37     <ul>
  38       <li><a href="#is_holder">Class template <code>is_holder</code></a></li>
  39       <li><a href="#holder_construct">Class template <code>holder</code></a></li>
  40     </ul>
  41   </li>
  42   <li><a href="#static_holder_fwd_synopsis">Header
  43     <code>"boost/flyweight/static_holder_fwd.hpp"</code> synopsis</a>
  44   </li>
  45   <li><a href="#static_holder_synopsis">Header
  46     <code>"boost/flyweight/static_holder.hpp"</code> synopsis</a>
  47     <ul>
  48       <li><a href="#static_holder_class">Class template <code>static_holder_class</code></a></li>
  49       <li><a href="#static_holder">Class <code>static_holder</code></a></li>
  50     </ul>
  51   </li>
  52   <li><a href="#intermodule_holder_fwd_synopsis">Header
  53     <code>"boost/flyweight/intermodule_holder_fwd.hpp"</code> synopsis</a>
  54   </li>
  55   <li><a href="#intermodule_holder_synopsis">Header
  56     <code>"boost/flyweight/intermodule_holder.hpp"</code> synopsis</a>
  57     <ul>
  58       <li><a href="#intermodule_holder_class">Class template <code>intermodule_holder_class</code></a></li>
  59       <li><a href="#intermodule_holder">Class <code>intermodule_holder</code></a></li>
  60     </ul>
  61   </li>
  62 </ul>
  63
  64 <h2><a name="holder">Holders and holder specifiers</a></h2>
  65
  66 <p>
  67 Given a type <code>C</code>, a type <code>Holder</code> is said to be a <i>holder
  68 of <code>C</code></i> if the expression <code>Holder::get()</code> returns
  69 a reference to a default initialized <code>C</code> object unique to
  70 <code>Holder</code>. No invocation of <code>Holder::get()</code>, except possibly
  71 the first one in the program, does throw.
  72 <a href="flyweight.html#flyweight"><code>flyweight</code></a>
  73 privately uses a holder to instantiate a <a href="factories.html#factory">factory</a>
  74 and some additional data (like a <a href="locking.html#preliminary">mutex</a> for
  75 internal synchronization) unique to each instantiation type of the class template.
  76 </p>
  77
  78 <p>
  79 A type <code>S</code> is a <i>holder specifier</i> if:
  80 <ol>
  81   <li>One of the following conditions is satisfied:
  82     <ol type="a">
  83       <li><a href="#is_holder"><code>is_holder&lt;S&gt;::type</code></a> is
  84       <a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::true_</code></a>,</li>
  85       <li><code>S</code> is of the form <a href="#holder_construct"><code>holder&lt;S'&gt;</code></a>.</li>
  86     </ol>
  87   </li>
  88   <li><code>S</code>, or <code>S'</code> if (b) applies, is an
  89     <a href="../../../mpl/doc/refmanual/lambda-expression.html"><code>MPL Lambda
  90     Expression</code></a> such that invoking it with type <code>C</code> resolves to
  91     a holder of <code>C</code>.
  92   </li>
  93 </ol>
  94 </p>
  95
  96 <h2><a name="holder_tag_synopsis">Header
  97 <a href="../../../../boost/flyweight/holder_tag.hpp"><code>"boost/flyweight/holder_tag.hpp"</code></a> synopsis</a></h2>
  98
  99 <blockquote><pre>
 100 <span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
 101
 102 <span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
 103
 104 <span class=keyword>struct</span> <span class=identifier>holder_marker</span><span class=special>;</span>
 105
 106 <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>
 107 <span class=keyword>struct</span> <span class=identifier>is_holder</span><span class=special>;</span>
 108
 109 <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>
 110 <span class=keyword>struct</span> <span class=identifier>holder</span><span class=special>;</span>
 111
 112 <span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
 113
 114 <span class=special>}</span> <span class=comment>// namespace boost</span>
 115 </pre></blockquote>
 116
 117 <h3><a name="is_holder">Class template <code>is_holder</code></a></h3>
 118
 119 <p>
 120 Unless specialized by the user, <code>is_holder&lt;T&gt;::type</code> is
 121 <a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::true_</code></a>
 122 if <code>T</code> is derived from <code>holder_marker</code>, and it is
 123 <a href="../../../mpl/doc/refmanual/bool.html"><code>boost::mpl::false_</code></a>
 124 otherwise.
 125 </p>
 126
 127 <h3><a name="holder_construct">Class template <code>holder</code></a></h3>
 128
 129 <p>
 130 <code>holder&lt;T&gt;</code> is a syntactic construct meant to indicate
 131 that <code>T</code> is a holder specifier without resorting to the
 132 mechanisms provided by the <code>is_holder</code> class template.
 133 </p>
 134
 135 <h2><a name="static_holder_fwd_synopsis">Header
 136 <a href="../../../../boost/flyweight/static_holder_fwd.hpp"><code>"boost/flyweight/static_holder_fwd.hpp"</code></a> synopsis</a></h2>
 137
 138 <blockquote><pre>
 139 <span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
 140
 141 <span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
 142
 143 <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>
 144 <span class=keyword>struct</span> <span class=identifier>static_holder_class</span><span class=special>;</span>
 145
 146 <span class=keyword>struct</span> <span class=identifier>static_holder</span><span class=special>;</span>
 147
 148 <span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
 149
 150 <span class=special>}</span> <span class=comment>// namespace boost</span>
 151 </pre></blockquote>
 152
 153 <p>
 154 <code>static_holder_fwd.hpp</code> forward declares
 155 <a href="#static_holder_class"><code>static_holder_class</code></a>
 156 and <a href="#static_holder"><code>static_holder</code></a>.
 157 </p>
 158
 159 <h2><a name="static_holder_synopsis">Header
 160 <a href="../../../../boost/flyweight/static_holder.hpp"><code>"boost/flyweight/static_holder.hpp"</code></a> synopsis</a></h2>
 161
 162 <h3><a name="static_holder_class">Class template <code>static_holder_class</code></a></h3>
 163
 164 <p>
 165 <code>static_holder_class&lt;C&gt;</code> keeps its unique instance of <code>C</code> as a
 166 local static object.
 167 </p>
 168
 169 <h3><a name="static_holder">Class <code>static_holder</code></a></h3>
 170
 171 <p>
 172 <a href="#holder"><code>Holder Specifier</code></a> for <a href="#static_holder_class"><code>static_holder_class</code></a>.
 173 </p>
 174
 175 <h2><a name="intermodule_holder_fwd_synopsis">Header
 176 <a href="../../../../boost/flyweight/intermodule_holder_fwd.hpp"><code>"boost/flyweight/intermodule_holder_fwd.hpp"</code></a> synopsis</a></h2>
 177
 178 <blockquote><pre>
 179 <span class=keyword>namespace</span> <span class=identifier>boost</span><span class=special>{</span>
 180
 181 <span class=keyword>namespace</span> <span class=identifier>flyweights</span><span class=special>{</span>
 182
 183 <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>
 184 <span class=keyword>struct</span> <span class=identifier>intermodule_holder_class</span><span class=special>;</span>
 185
 186 <span class=keyword>struct</span> <span class=identifier>intermodule_holder</span><span class=special>;</span>
 187
 188 <span class=special>}</span> <span class=comment>// namespace boost::flyweights</span>
 189
 190 <span class=special>}</span> <span class=comment>// namespace boost</span>
 191 </pre></blockquote>
 192
 193 <p>
 194 <code>intermodule_holder_fwd.hpp</code> forward declares
 195 <a href="#intermodule_holder_class"><code>intermodule_holder_class</code></a>
 196 and <a href="#intermodule_holder"><code>intermodule_holder</code></a>.
 197 </p>
 198
 199 <h2><a name="intermodule_holder_synopsis">Header
 200 <a href="../../../../boost/flyweight/intermodule_holder.hpp"><code>"boost/flyweight/intermodule_holder.hpp"</code></a> synopsis</a></h2>
 201
 202 <h3><a name="intermodule_holder_class">Class template <code>intermodule_holder_class</code></a></h3>
 203
 204 <p>
 205 <code>intermodule_holder_class&lt;C&gt;</code> maintains a <code>C</code>
 206 instance which is unique even across different dynamically linked modules of
 207 the program using this same type. In general, this guarantee is not provided by
 208 <a href="#static_holder_class"><code>static_holder_class</code></a>, as most
 209 C++ implementations are not able to merge duplicates of static variables stored
 210 in different dynamic modules of a program.
 211 </p>
 212
 213 <h3><a name="intermodule_holder">Class <code>intermodule_holder</code></a></h3>
 214
 215 <p>
 216 <a href="#holder"><code>Holder Specifier</code></a> for <a href="#intermodule_holder_class"><code>intermodule_holder_class</code></a>.
 217 </p>
 218
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 231 <br>
 232
 233 <p>Revised August 11th 2008</p>
 234
 235 <p>&copy; Copyright 2006-2008 Joaqu&iacute;n M L&oacute;pez Mu&ntilde;oz.
 236 Distributed under the Boost Software
 237 License, Version 1.0. (See accompanying file <a href="../../../../LICENSE_1_0.txt">
 238 LICENSE_1_0.txt</a> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">
 239 http://www.boost.org/LICENSE_1_0.txt</a>)
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