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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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