ceph/src/boost/libs/utility/MultiPassInputIterator.html

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  15
  16   <h2><a name="concept:MultiPassInputIterator" id=
  17   "concept:MultiPassInputIterator"></a> Multi-Pass Input Iterator</h2>
  18
  19   <p>This concept is a refinement of <a href=
  20   "http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>, adding
  21   the requirements that the iterator can be used to make multiple passes
  22   through a range, and that if <tt>it1 == it2</tt> and <tt>it1</tt> is
  23   dereferenceable then <tt>++it1 == ++it2</tt>. The Multi-Pass Input Iterator
  24   is very similar to the <a href=
  25   "http://www.sgi.com/tech/stl/ForwardIterator.html">Forward Iterator</a>.
  26   The only difference is that a <a href=
  27   "http://www.sgi.com/tech/stl/ForwardIterator.html">Forward Iterator</a>
  28   requires the <tt>reference</tt> type to be <tt>value_type&amp;</tt>,
  29   whereas MultiPassInputIterator is like <a href=
  30   "http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a> in that
  31   the <tt>reference</tt> type merely has to be convertible to
  32   <tt>value_type</tt>.</p>
  33
  34   <h3>Design Notes</h3>
  35
  36   <p>comments by Valentin Bonnard:</p>
  37
  38   <p>I think that introducing Multi-Pass Input Iterator isn't the right
  39   solution. Do you also want to define Multi-Pass Bidirectionnal Iterator and
  40   Multi-Pass Random Access Iterator ? I don't, definitly. It only confuses
  41   the issue. The problem lies into the existing hierarchy of iterators, which
  42   mixes movabillity, modifiabillity and lvalue-ness, and these are clearly
  43   independant.</p>
  44
  45   <p>The terms Forward, Bidirectionnal and Random Access are about
  46   movabillity and shouldn't be used to mean anything else. In a completly
  47   orthogonal way, iterators can be immutable, mutable, or neither. Lvalueness
  48   of iterators is also orthogonal with immutabillity. With these clean
  49   concepts, your Multi-Pass Input Iterator is just called a Forward
  50   Iterator.</p>
  51
  52   <p>Other translations are:<br>
  53   std::Forward Iterator -&gt; ForwardIterator &amp; Lvalue Iterator<br>
  54   std::Bidirectionnal Iterator -&gt; Bidirectionnal Iterator &amp; Lvalue
  55   Iterator<br>
  56   std::Random Access Iterator -&gt; Random Access Iterator &amp; Lvalue
  57   Iterator<br></p>
  58
  59   <p>Note that in practice the only operation not allowed on my Forward
  60   Iterator which is allowed on std::Forward Iterator is <tt>&amp;*it</tt>. I
  61   think that <tt>&amp;*</tt> is rarely needed in generic code.</p>
  62
  63   <p>reply by Jeremy Siek:</p>
  64
  65   <p>The above analysis by Valentin is right on. Of course, there is the
  66   problem with backward compatibility. The current STL implementations are
  67   based on the old definition of Forward Iterator. The right course of action
  68   is to get Forward Iterator, etc. changed in the C++ standard. Once that is
  69   done we can drop Multi-Pass Input Iterator.<br></p>
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  76   <p>Revised
  77   <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05
  78   December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
  79
  80   <table summary="">
  81     <tr valign="top">
  82       <td nowrap><i>Copyright &copy; 2000</i></td>
  83
  84       <td><i><a href="http://www.lsc.nd.edu/~jsiek">Jeremy Siek</a>, Univ.of
  85       Notre Dame (<a href=
  86       "mailto:jsiek@lsc.nd.edu">jsiek@lsc.nd.edu</a>)</i></td>
  87     </tr>
  88   </table>
  89
  90   <p><i>Distributed under the Boost Software License, Version 1.0. (See
  91   accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
  92   copy at <a href=
  93   "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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