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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&</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 -> ForwardIterator & Lvalue Iterator<br>
- std::Bidirectionnal Iterator -> Bidirectionnal Iterator & Lvalue
- Iterator<br>
- std::Random Access Iterator -> Random Access Iterator & 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>&*it</tt>. I
- think that <tt>&*</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 © 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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