[Boost-bugs] [Boost C++ Libraries] #4647: BOOST_CONCEPT_ASSERT((RandomAccessIterator<boost::transform_iterator>)) fails

Subject: [Boost-bugs] [Boost C++ Libraries] #4647: BOOST_CONCEPT_ASSERT((RandomAccessIterator<boost::transform_iterator>)) fails
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-09-13 21:21:14

#4647: BOOST_CONCEPT_ASSERT((RandomAccessIterator<boost::transform_iterator>))
fails
------------------------------------------------+---------------------------
 Reporter:  Ilya Murav'jov <muravev@…>          |       Owner:         
     Type:  Bugs                                |      Status:  new    
Milestone:  To Be Determined                    |   Component:  None   
  Version:  Boost 1.44.0                        |    Severity:  Problem
 Keywords:                                      |  
------------------------------------------------+---------------------------
 {{{#!c++
 #include <boost/iterator/transform_iterator.hpp>
 #include <boost/concept_check.hpp> // RandomAccessIterator
 #include <vector>

 typedef std::vector<int>::iterator int_iterator;
 typedef boost::transform_iterator<int(*)(int), int_iterator> tr_iterator;
 BOOST_CONCEPT_ASSERT((boost::RandomAccessIterator<tr_iterator>)); // fails
 }}}

 with an error like this:

 libs/boost-lib/boost/concept_check.hpp: In destructor
 'boost::Convertible<X, Y>::~Convertible() [with X =
 boost::detail::iterator_category_with_traversal<std::input_iterator_tag,
 boost::random_access_traversal_tag>, Y =
 std::random_access_iterator_tag]':
 libs/boost-lib/boost/concept/detail/general.hpp:38:   instantiated from
 'static void
 boost::concepts::requirement<boost::concepts::failed************
 Model::************>::failed() [with Model =
 boost::Convertible<boost::detail::iterator_category_with_traversal<std::input_iterator_tag,
 boost::random_access_traversal_tag>, std::random_access_iterator_tag>]'
 libs/boost-lib/boost/concept_check.hpp:566:   instantiated from
 'boost::RandomAccessIterator<TT>::~RandomAccessIterator() [with TT =
 boost::transform_iterator<int (*)(int), __gnu_cxx::__normal_iterator<int*,
 std::vector<int, std::allocator<int> > >, boost::use_default,
 boost::use_default>]'
 libs/boost-lib/boost/concept/detail/general.hpp:38:   instantiated from
 'static void
 boost::concepts::requirement<boost::concepts::failed************
 Model::************>::failed() [with Model =
 boost::RandomAccessIterator<boost::transform_iterator<int (*)(int),
 __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> >
 >, boost::use_default, boost::use_default> >]'
 src/mlib/tests/test_iterator.cpp:123:   instantiated from here
 libs/boost-lib/boost/concept_check.hpp:207: error: conversion from
 'boost::detail::iterator_category_with_traversal<std::input_iterator_tag,
 boost::random_access_traversal_tag>' to non-scalar type
 'std::random_access_iterator_tag' requested

 This is because iterator_adaptor turns std::random_access_iterator_tag
 into boost::random_access_traversal_tag, then iterator_facade turns it
 into iterator_category_with_traversal<std::input_iterator_tag,
 boost::random_access_traversal_tag>. The check fails if

 {{{#!c++
 typedef boost::transform_iterator<int(*)(int), int_iterator> tr_iterator;
 }}}

 but not if

 {{{#!c++
 typedef boost::transform_iterator<int&(*)(int), int_iterator> tr_iterator;
 }}}

 Why it matters for me: I try to use "any_iterator", which has two
 versions,
 http://thbecker.net/free_software_utilities/type_erasure_for_cpp_iterators/start_page.html

 (Thomas Becker's) and
 http://stlab.adobe.com/classadobe_1_1any__iterator.html (Adobe's). The
 first one do many efforts to avoid this bug but still check iterators for
 compatibility (see traversal_types_erasure_compatible<>), the second just
 fails with an error like this.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4647>
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