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  <h2><a name="concept:MultiPassInputIterator" id=
  "concept:MultiPassInputIterator"></a> Multi-Pass Input Iterator</h2>

  <p>This concept is a refinement of <a href=
  "http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a>, adding
  the requirements that the iterator can be used to make multiple passes
  through a range, and that if <tt>it1 == it2</tt> and <tt>it1</tt> is
  dereferenceable then <tt>++it1 == ++it2</tt>. The Multi-Pass Input Iterator
  is very similar to the <a href=
  "http://www.sgi.com/tech/stl/ForwardIterator.html">Forward Iterator</a>.
  The only difference is that a <a href=
  "http://www.sgi.com/tech/stl/ForwardIterator.html">Forward Iterator</a>
  requires the <tt>reference</tt> type to be <tt>value_type&amp;</tt>,
  whereas MultiPassInputIterator is like <a href=
  "http://www.sgi.com/tech/stl/InputIterator.html">Input Iterator</a> in that
  the <tt>reference</tt> type merely has to be convertible to
  <tt>value_type</tt>.</p>

  <h3>Design Notes</h3>

  <p>comments by Valentin Bonnard:</p>

  <p>I think that introducing Multi-Pass Input Iterator isn't the right
  solution. Do you also want to define Multi-Pass Bidirectionnal Iterator and
  Multi-Pass Random Access Iterator ? I don't, definitly. It only confuses
  the issue. The problem lies into the existing hierarchy of iterators, which
  mixes movabillity, modifiabillity and lvalue-ness, and these are clearly
  independant.</p>

  <p>The terms Forward, Bidirectionnal and Random Access are about
  movabillity and shouldn't be used to mean anything else. In a completly
  orthogonal way, iterators can be immutable, mutable, or neither. Lvalueness
  of iterators is also orthogonal with immutabillity. With these clean
  concepts, your Multi-Pass Input Iterator is just called a Forward
  Iterator.</p>

  <p>Other translations are:<br>
  std::Forward Iterator -&gt; ForwardIterator &amp; Lvalue Iterator<br>
  std::Bidirectionnal Iterator -&gt; Bidirectionnal Iterator &amp; Lvalue
  Iterator<br>
  std::Random Access Iterator -&gt; Random Access Iterator &amp; Lvalue
  Iterator<br></p>

  <p>Note that in practice the only operation not allowed on my Forward
  Iterator which is allowed on std::Forward Iterator is <tt>&amp;*it</tt>. I
  think that <tt>&amp;*</tt> is rarely needed in generic code.</p>

  <p>reply by Jeremy Siek:</p>

  <p>The above analysis by Valentin is right on. Of course, there is the
  problem with backward compatibility. The current STL implementations are
  based on the old definition of Forward Iterator. The right course of action
  is to get Forward Iterator, etc. changed in the C++ standard. Once that is
  done we can drop Multi-Pass Input Iterator.<br></p>
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  <p>Revised 
  <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05
  December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>

  <table summary="">
    <tr valign="top">
      <td nowrap><i>Copyright &copy; 2000</i></td>

      <td><i><a href="http://www.lsc.nd.edu/~jsiek">Jeremy Siek</a>, Univ.of
      Notre Dame (<a href=
      "mailto:jsiek@lsc.nd.edu">jsiek@lsc.nd.edu</a>)</i></td>
    </tr>
  </table>

  <p><i>Distributed under the Boost Software License, Version 1.0. (See
  accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
  copy at <a href=
  "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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