[Boost-bugs] [Boost C++ Libraries] #1019: iterator_facade::pointer should be the return type of operator-> (DR 445)

Subject: [Boost-bugs] [Boost C++ Libraries] #1019: iterator_facade::pointer should be the return type of operator-> (DR 445)
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2007-05-30 21:59:50

#1019: iterator_facade::pointer should be the return type of operator-> (DR 445)
--------------------------+-------------------------------------------------
 Reporter:  Niels Dekker  |        Type:  Bugs          
   Status:  new           |   Milestone:  Boost 1.34.1  
Component:  iterator      |     Version:  release 1.34.0
 Severity:  Problem       |    Keywords:                
--------------------------+-------------------------------------------------
 The definition of iterator_facade does not agree with the resolution of
 Standard Library Defect Report 445, submitted by David Abrahams, 2003-12-
 09. [[BR]]
 http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#445


 DR 445 is resolved within the current Draft of the Standard, as follows
 (Iterator traits, section 24.3.1):[[BR]]
 '' iterator_traits<Iterator>::reference '' [[BR]]
 '' iterator_traits<Iterator>::pointer '' [[BR]]
 ''shall be defined as the iterator’s reference and pointer types, that is,
 for an iterator object a, the same type as the type of *a and a->,
 respectively.'' [[BR]]
 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2135.pdf


 On the other hand, iterator_facade::pointer is a raw pointer, while
 iterator_facade::operator->() returns operator_arrow_result::type, which
 may be a proxy.

 To conform to the resolution of DR 445, iterator_facade::pointer should be
 defined as the return type of operator->(), e.g. (assuming that
 ''raw_pointer'' is the original raw pointer to the value_type):

 {{{
   typedef typename operator_arrow_result<
       value_type
     , reference
     , raw_pointer
     >::type pointer;
 }}}

 More discussion about this issue:

 comp.lang.c++.moderated, Sep 29 2005 [[BR]]
 Re: iterator dereference requirements [[BR]]
 http://groups.google.com/group/comp.lang.c++.moderated/msg/0f332bcd9a911526


 comp.std.c++, March/April 2007 [[BR]]
 What should std::InputIterator<T>::pointer be? [n2193 / n2083] [[BR]]
 http://groups.google.com/groups/search?q=%22What+should+std%3A%3AInputIterator%3CT%3E%3A%3Apointer+be%3F%22


 comp.std.c++, May 2007 [[BR]]
 Testing new iterator concepts with ConceptGCC [[BR]]
 http://groups.google.com/group/comp.std.c++/tree/browse_frm/thread/9c40ffc2f6394ca0/590e75dfbb993cf6


 [I had some e-mail discussion with David Abrahams on this issue as well.]

-- 
Ticket URL: <http://svn.boost.org/trac/boost/ticket/1019>
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