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

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   4 <!--
   5 Copyright Douglas Gregor 2001-2004
   6 Copyright Frank Mori Hess 2007-2009
   7
   8 Distributed under the Boost Software License, Version 1.0. (See accompanying
   9 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  10 -->
  11 <header name="boost/signals2/optional_last_value.hpp" last-revision="$Date: 2007-03-06 16:51:55 -0500 (Tue, 06 Mar 2007) $">
  12   <namespace name="boost">
  13     <namespace name="signals2">
  14       <class name="optional_last_value">
  15         <template>
  16           <template-type-parameter name="T"/>
  17         </template>
  18
  19         <purpose>Evaluate an <conceptname>InputIterator</conceptname> sequence and return
  20           a boost::optional which contains the last value in the sequence, or an
  21           empty <classname>boost::optional</classname> if the sequence was empty.</purpose>
  22         <description>
  23           <para>
  24             <code>optional_last_value</code> is the default Combiner template type for signals in the
  25             Boost.Signals2 library.  The advantage of <code>optional_last_value</code> over
  26             <classname>signals2::last_value</classname> is that <code>optional_last_value</code>
  27             can return an empty <classname>boost::optional</classname>. rather
  28             than throwing an exception, when
  29             its <code>InputIterator</code> sequence is empty.
  30           </para>
  31         </description>
  32
  33         <typedef name="result_type"><type><classname>boost::optional</classname>&lt;T&gt;</type></typedef>
  34
  35         <method-group name="invocation">
  36           <method name="operator()" cv="const">
  37             <template>
  38               <template-type-parameter name="InputIterator"/>
  39             </template>
  40             <type>result_type</type>
  41             <parameter name="first">
  42               <paramtype>InputIterator</paramtype>
  43             </parameter>
  44             <parameter name="last">
  45               <paramtype>InputIterator</paramtype>
  46             </parameter>
  47
  48             <effects><para>Attempts to dereference every iterator in the sequence <computeroutput>[first, last)</computeroutput>.
  49               </para></effects>
  50             <returns>
  51               <para>
  52                 The result of the last successful iterator dereference, wrapped in a <classname>boost::optional</classname>.
  53                 The returned <code>optional</code> will be empty if no iterators were dereferenced.
  54               </para>
  55             </returns>
  56             <throws><para>Does not throw.</para></throws>
  57           </method>
  58         </method-group>
  59       </class>
  60
  61       <class-specialization name="optional_last_value">
  62         <template/>
  63         <specialization>
  64           <template-arg>void</template-arg>
  65         </specialization>
  66
  67         <purpose>Evaluate an InputIterator sequence.</purpose>
  68         <description>
  69           <para>This specialization of <classname>signals2::optional_last_value</classname> is provided
  70             to cope with the fact that there is no such thing as an
  71             <code><classname>optional</classname>&lt;void&gt;</code>, which
  72             <classname>optional_last_value</classname> would otherwise try to
  73             use as its <code>result_type</code>.  This specialization
  74             instead sets the <code>result_type</code> to be <code>void</code>.
  75           </para>
  76         </description>
  77
  78         <typedef name="result_type">
  79           <type>void</type>
  80         </typedef>
  81
  82         <method-group name="invocation">
  83           <method name="operator()" cv="const">
  84             <template>
  85               <template-type-parameter name="InputIterator"/>
  86             </template>
  87             <type>result_type</type>
  88             <parameter name="first">
  89               <paramtype>InputIterator</paramtype>
  90             </parameter>
  91             <parameter name="last">
  92               <paramtype>InputIterator</paramtype>
  93             </parameter>
  94
  95             <effects><para>Attempts to dereference every iterator in the sequence <computeroutput>[first, last)</computeroutput>.
  96               </para></effects>
  97           </method>
  98         </method-group>
  99       </class-specialization>
 100     </namespace>
 101   </namespace>
 102 </header>