ceph/src/boost/libs/signals2/doc/reference/visit_each.xml

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   5 Copyright Douglas Gregor 2001-2004
   6
   7 Distributed under the Boost Software License, Version 1.0. (See accompanying
   8 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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  10 <header name="boost/visit_each.hpp" last-revision="$Date: 2007-03-06 16:51:55 -0500 (Tue, 06 Mar 2007) $">
  11   <namespace name="boost">
  12     <function name="visit_each">
  13       <template>
  14         <template-type-parameter name="Visitor"/>
  15         <template-type-parameter name="T"/>
  16       </template>
  17       <type>void</type>
  18       <parameter name="visitor">
  19         <paramtype>const Visitor&amp;</paramtype>
  20       </parameter>
  21       <parameter name="t">
  22         <paramtype>const T&amp;</paramtype>
  23       </parameter>
  24       <parameter>
  25         <paramtype>int</paramtype>
  26       </parameter>
  27
  28       <purpose>Allow limited exploration of class members.</purpose>
  29
  30       <description>
  31         <para>The <functionname>visit_each</functionname> mechanism
  32         allows a visitor to be applied to every subobject in a given
  33         object. It was used by the Signals library to discover (now deprecated)
  34         <classname>signals::trackable</classname> objects within a
  35         function object, but other uses may surface if used
  36         universally (e.g., conservative garbage collection). To fit
  37         within the <functionname>visit_each</functionname> framework,
  38         a <functionname>visit_each</functionname> overload must be
  39         supplied for each object type. </para>
  40       </description>
  41
  42       <effects><para><code>visitor(t)</code>, and for
  43       every subobject <code>x</code> of
  44       <code>t</code>:
  45         <itemizedlist>
  46           <listitem><para>If <code>x</code> is a reference, <code>visit_each(visitor, <functionname>ref</functionname>(x), 0)</code></para></listitem>
  47           <listitem><para>Otherwise, <code>visit_each(visitor, x, 0)</code></para></listitem>
  48         </itemizedlist>
  49       </para></effects>
  50
  51       <notes><para>The third parameter is
  52       <code>long</code> for the fallback version
  53       of <functionname>visit_each</functionname> and the argument
  54       supplied to this third paramter must always be 0. The third
  55       parameter is an artifact of the widespread lack of proper
  56       function template ordering, and will be removed in the future.</para>
  57
  58       <para>Library authors will be expected to add additional
  59       overloads that specialize the T argument for their classes, so
  60       that subobjects can be visited.</para>
  61
  62       <para>Calls to visit_each are required to be unqualified, to
  63       enable argument-dependent lookup.</para></notes>
  64     </function>
  65   </namespace>
  66 </header>