Re: [Boost-bugs] [Boost C++ Libraries] #13094: boost::adaptors::transform fails to preserve bidirectional behavior of range

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #13094: boost::adaptors::transform fails to preserve bidirectional behavior of range
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-06-24 00:52:08

#13094: boost::adaptors::transform fails to preserve bidirectional behavior of
range
-------------------------------------+-------------------------------------
  Reporter:  Jake Cobb               |      Owner:  neilgroves
  <jake.cobb@…>                      |
      Type:  Bugs                    |     Status:  new
 Milestone:  To Be Determined        |  Component:  range
   Version:  Boost 1.64.0            |   Severity:  Problem
Resolution:                          |   Keywords:  range adaptors
                                     |  transform
-------------------------------------+-------------------------------------

Comment (by Jake Cobb <jake.cobb@…>):

 By the way I see this with both clang and Visual Studio libraries.  It
 seems that `std::advance`, `std::prev`, etc are relying on
 `std::iterator_traits<Iter>::iterator_category` tag dispatch, which for
 `std::vector` yields:

 `std::random_access_iterator_tag`

 But for `boost::adaptors::transform` yields:

 `boost::iterators::detail::iterator_category_with_traversal<std::input_iterator_tag,
 boost::iterators::random_access_traversal_tag>`

 It looks like there may be code for boost to understand the standard
 library `iterator_category` tags in terms of traversals, but the opposite
 does not work; this causes behavior changes when passing to code using
 standard library conventions when the code is modified from passing
 standard types to boost adaptor types.

--
Ticket URL: <https://svn.boost.org/trac10/boost/ticket/13094#comment:1>
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