ceph/src/boost/libs/mpl/doc/refmanual/forward-iterator.html

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  14 <div class="section" id="forward-iterator">
  15 <h1><a class="toc-backref" href="./iterators-concepts.html#id1450">Forward Iterator</a></h1>
  16 <div class="section" id="id384">
  17 <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
  18 <p>A <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a> <tt class="literal"><span class="pre">i</span></tt> is a type that represents a positional reference
  19 to an element of a <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>. It allows to access the element through
  20 a dereference operation, and provides a way to obtain an iterator to
  21 the next element in a sequence.</p>
  22 <!-- A [Forward Iterator] guarantees a linear traversal over
  23 the sequence. -->
  24 </div>
  25 <div class="section" id="id385">
  26 <h3><a class="subsection-title" href="#definitions" name="definitions">Definitions</a></h3>
  27 <ul class="simple">
  28 <li>An iterator can be <cite>dereferenceable</cite>, meaning that <tt class="literal"><span class="pre"><a href="./deref.html" class="identifier">deref</a>&lt;i&gt;::type</span></tt>
  29 is a well-defined expression.</li>
  30 <li>An iterator is <cite>past-the-end</cite> if it points beyond the last element of a
  31 sequence; past-the-end iterators are non-dereferenceable.</li>
  32 <li>An iterator <tt class="literal"><span class="pre">i</span></tt> is <cite>incrementable</cite> if there is a &quot;next&quot; iterator, that
  33 is, if <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a>&lt;i&gt;::type</span></tt> expression is well-defined; past-the-end iterators are
  34 not incrementable.</li>
  35 <li>Two iterators into the same sequence are <cite>equivalent</cite> if they have the same
  36 type.</li>
  37 <li>An iterator <tt class="literal"><span class="pre">j</span></tt> is <cite>reachable</cite> from an iterator <tt class="literal"><span class="pre">i</span></tt> if , after recursive
  38 application of <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a></span></tt> metafunction to <tt class="literal"><span class="pre">i</span></tt> a finite number of times, <tt class="literal"><span class="pre">i</span></tt>
  39 is equivalent to <tt class="literal"><span class="pre">j</span></tt>.</li>
  40 <li>The notation [<tt class="literal"><span class="pre">i</span></tt>,<tt class="literal"><span class="pre">j</span></tt>) refers to a <cite>range</cite> of iterators beginning with
  41 <tt class="literal"><span class="pre">i</span></tt> and up to but not including <tt class="literal"><span class="pre">j</span></tt>.</li>
  42 <li>The range [<tt class="literal"><span class="pre">i</span></tt>,<tt class="literal"><span class="pre">j</span></tt>) is a <cite>valid range</cite> if <tt class="literal"><span class="pre">j</span></tt> is reachable from <tt class="literal"><span class="pre">i</span></tt>.</li>
  43 </ul>
  44 </div>
  45 <div class="section" id="id386">
  46 <h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3>
  47 <table border="1" class="docutils table">
  48 <colgroup>
  49 <col width="25%" />
  50 <col width="46%" />
  51 <col width="29%" />
  52 </colgroup>
  53 <thead valign="bottom">
  54 <tr><th class="head">Expression</th>
  55 <th class="head">Type</th>
  56 <th class="head">Complexity</th>
  57 </tr>
  58 </thead>
  59 <tbody valign="top">
  60 <tr><td><tt class="literal"><span class="pre"><a href="./deref.html" class="identifier">deref</a>&lt;i&gt;::type</span></tt></td>
  61 <td>Any type</td>
  62 <td>Amortized constant time</td>
  63 </tr>
  64 <tr><td><tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a>&lt;i&gt;::type</span></tt></td>
  65 <td><a class="reference internal" href="./forward-iterator.html">Forward Iterator</a></td>
  66 <td>Amortized constant time</td>
  67 </tr>
  68 <tr><td><tt class="literal"><span class="pre">i::category</span></tt></td>
  69 <td><a class="reference internal" href="./integral-constant.html">Integral Constant</a>, convertible
  70 to <tt class="literal"><span class="pre">forward_iterator_tag</span></tt></td>
  71 <td>Constant time</td>
  72 </tr>
  73 </tbody>
  74 </table>
  75 </div>
  76 <div class="section" id="id387">
  77 <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
  78 <pre class="literal-block">
  79 typedef <a href="./deref.html" class="identifier">deref</a>&lt;i&gt;::type j;
  80 </pre>
  81 <table class="docutils field-list" frame="void" rules="none">
  82 <col class="field-name" />
  83 <col class="field-body" />
  84 <tbody valign="top">
  85 <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">i</span></tt> is dereferenceable</td>
  86 </tr>
  87 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">j</span></tt> is identical to the type of the pointed element</td>
  88 </tr>
  89 </tbody>
  90 </table>
  91 <!-- .......................................................................... -->
  92 <pre class="literal-block">
  93 typedef <a href="./next.html" class="identifier">next</a>&lt;i&gt;::type j;
  94 </pre>
  95 <table class="docutils field-list" frame="void" rules="none">
  96 <col class="field-name" />
  97 <col class="field-body" />
  98 <tbody valign="top">
  99 <tr class="field"><th class="field-name">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">i</span></tt> is incrementable</td>
 100 </tr>
 101 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">j</span></tt> is the next iterator in a sequence</td>
 102 </tr>
 103 <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><tt class="literal"><span class="pre">j</span></tt> is dereferenceable or past-the-end</td>
 104 </tr>
 105 </tbody>
 106 </table>
 107 <!-- .......................................................................... -->
 108 <pre class="literal-block">
 109 typedef i::category c;
 110 </pre>
 111 <table class="docutils field-list" frame="void" rules="none">
 112 <col class="field-name" />
 113 <col class="field-body" />
 114 <tbody valign="top">
 115 <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">c</span></tt> is identical to the iterator's category tag</td>
 116 </tr>
 117 </tbody>
 118 </table>
 119 </div>
 120 <div class="section" id="id388">
 121 <h3><a class="subsection-title" href="#invariants" name="invariants">Invariants</a></h3>
 122 <p>For any forward iterators <tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> the following invariants always hold:</p>
 123 <ul class="simple">
 124 <li><tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> are equivalent if and only if they are pointing to the same
 125 element.</li>
 126 <li>If <tt class="literal"><span class="pre">i</span></tt> is dereferenceable, and <tt class="literal"><span class="pre">j</span></tt> is equivalent to <tt class="literal"><span class="pre">i</span></tt>, then <tt class="literal"><span class="pre">j</span></tt> is
 127 dereferenceable as well.</li>
 128 <li>If <tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> are equivalent and dereferenceable, then <tt class="literal"><span class="pre"><a href="./deref.html" class="identifier">deref</a>&lt;i&gt;::type</span></tt>
 129 and <tt class="literal"><span class="pre"><a href="./deref.html" class="identifier">deref</a>&lt;j&gt;::type</span></tt> are identical.</li>
 130 <li>If <tt class="literal"><span class="pre">i</span></tt> is incrementable, and <tt class="literal"><span class="pre">j</span></tt> is equivalent to <tt class="literal"><span class="pre">i</span></tt>, then <tt class="literal"><span class="pre">j</span></tt> is
 131 incrementable as well.</li>
 132 <li>If <tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> are equivalent and incrementable, then <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a>&lt;i&gt;::type</span></tt>
 133 and <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a>&lt;j&gt;::type</span></tt> are equivalent.</li>
 134 </ul>
 135 </div>
 136 <div class="section" id="id389">
 137 <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
 138 <p><a class="reference internal" href="./iterators.html">Iterators</a>, <a class="reference internal" href="./bidirectional-iterator.html">Bidirectional Iterator</a>, <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference internal" href="./deref.html">deref</a>, <a class="reference internal" href="./next.html">next</a></p>
 139 <!-- Iterators/Concepts//Bidirectional Iterator |20 -->
 140 </div>
 141 </div>
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