Re: [Boost-bugs] [Boost C++ Libraries] #2640: counting_iterator::reference lifetime tied to iterator

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #2640: counting_iterator::reference lifetime tied to iterator
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-01-14 16:50:51

#2640: counting_iterator::reference lifetime tied to iterator
---------------------------+------------------------------------------------
  Reporter:  schoedl       |       Owner:  dave                              
      Type:  Bugs          |      Status:  new                               
 Milestone:  Boost 1.38.0  |   Component:  iterator                          
   Version:  Boost 1.37.0  |    Severity:  Problem                           
Resolution:                |    Keywords:  counting_iterator reverse_iterator
---------------------------+------------------------------------------------

Comment (by dave):

 The history of iterators that own the object they reference is somewhat
 complicated.  {{{counting_iterator}}} does own its referent.  To be a
 valid forward iterator, its reference type must be a true C++ reference.
 Otherwise, it would be limited to input iterator.  Trying to accomodate
 forward iterators that store their referent caused innumerable contortions
 in the design of this library.

 However, recent re-readings of the C++03 standard make it clear to me that
 such iterators are not allowed to be forward iterators anyway.  In
 particular, below table 74 it says:

 > — If a and b are both dereferenceable, then a == b if and only if *a and
 *b are the same object.

 So IMO, the library design needs to be revisited in terms of this new
 understanding.  I don't want to address it piecemeal, because anything we
 do will break someone's code, and I want to make those changes all at
 once.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/2640#comment:2>
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