ceph/src/boost/libs/iterator/doc/iterator_traits.html

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  15 <div class="document" id="iterator-traits">
  16 <h1 class="title">Iterator Traits</h1>
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  21 <tr><th class="docinfo-name">Author:</th>
  22 <td>David Abrahams</td></tr>
  23 <tr><th class="docinfo-name">Contact:</th>
  24 <td><a class="first last reference external" href="mailto:dave&#64;boost-consulting.com">dave&#64;boost-consulting.com</a></td></tr>
  25 <tr><th class="docinfo-name">Organization:</th>
  26 <td><a class="first last reference external" href="http://www.boost-consulting.com">Boost Consulting</a></td></tr>
  27 <tr><th class="docinfo-name">Date:</th>
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  29 <tr><th class="docinfo-name">Copyright:</th>
  30 <td>Copyright David Abrahams 2004.</td></tr>
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  40 <tr class="field"><th class="field-name">abstract:</th><td class="field-body">Header <tt class="docutils literal">&lt;boost/iterator/iterator_traits.hpp&gt;</tt> provides
  41 the ability to access an iterator's associated types using
  42 MPL-compatible <a class="reference external" href="../../mpl/doc/index.html#metafunctions">metafunctions</a>.</td>
  43 </tr>
  44 </tbody>
  45 </table>
  46 <div class="section" id="overview">
  47 <h1>Overview</h1>
  48 <p><tt class="docutils literal"><span class="pre">std::iterator_traits</span></tt> provides access to five associated types
  49 of any iterator: its <tt class="docutils literal">value_type</tt>, <tt class="docutils literal">reference</tt>, <tt class="docutils literal">pointer</tt>,
  50 <tt class="docutils literal">iterator_category</tt>, and <tt class="docutils literal">difference_type</tt>.  Unfortunately,
  51 such a &quot;multi-valued&quot; traits template can be difficult to use in a
  52 metaprogramming context.  <tt class="docutils literal">&lt;boost/iterator/iterator_traits.hpp&gt;</tt>
  53 provides access to these types using a standard <a class="reference external" href="../../mpl/doc/index.html#metafunctions">metafunctions</a>.</p>
  54 </div>
  55 <div class="section" id="summary">
  56 <h1>Summary</h1>
  57 <p>Header <tt class="docutils literal">&lt;boost/iterator/iterator_traits.hpp&gt;</tt>:</p>
  58 <pre class="literal-block">
  59 template &lt;class Iterator&gt;
  60 struct iterator_value
  61 {
  62     typedef typename
  63       std::iterator_traits&lt;Iterator&gt;::value_type
  64     type;
  65 };
  66
  67 template &lt;class Iterator&gt;
  68 struct iterator_reference
  69 {
  70     typedef typename
  71       std::iterator_traits&lt;Iterator&gt;::reference
  72     type;
  73 };
  74
  75
  76 template &lt;class Iterator&gt;
  77 struct iterator_pointer
  78 {
  79     typedef typename
  80       std::iterator_traits&lt;Iterator&gt;::pointer
  81     type;
  82 };
  83
  84 template &lt;class Iterator&gt;
  85 struct iterator_difference
  86 {
  87     typedef typename
  88       detail::iterator_traits&lt;Iterator&gt;::difference_type
  89     type;
  90 };
  91
  92 template &lt;class Iterator&gt;
  93 struct iterator_category
  94 {
  95     typedef typename
  96       detail::iterator_traits&lt;Iterator&gt;::iterator_category
  97     type;
  98 };
  99 </pre>
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