on Wed Mar 04 2009, bismuth-AT-list.ru wrote:
There is probably a bug in boost::iterators library. boost::transform_iteartor degrade stl iterator_category. There is a code below, illustrating a problem(using VS2008 c++ compiler):
I just answered the trac ticket. It's not a bug. ForwardIterator (and thus Bidirectional and RandomAccessIterator) require their operator* to return a true reference to the value_type.
--------------------- #include <stdio.h> #include <tchar.h>
#include <vector> #include <boost/iterator/transform_iterator.hpp> #include <boost/static_assert.hpp>
struct Tr1: std::unary_function<unsigned, unsigned> { unsigned operator()(unsigned a)const { return a; } };
int _tmain(int argc, _TCHAR* argv[]) { typedef std::vector<unsigned>::iterator some_ra_iterator_t; typedef boost::transform_iterator<Tr1, some_ra_iterator_t> tr_iter_t;
BOOST_STATIC_ASSERT (( boost::is_convertible < std::iterator_traits<some_ra_iterator_t>::iterator_category, std::random_access_iterator_tag >::value ));
BOOST_STATIC_ASSERT (( ! boost::is_convertible < std::iterator_traits<tr_iter_t>::iterator_category, std::random_access_iterator_tag >::value ));
BOOST_STATIC_ASSERT (( boost::is_same < std::iterator_traits<tr_iter_t>::iterator_category, boost::detail::iterator_category_with_traversal < std::input_iterator_tag, //?! boost::random_access_traversal_tag > >::value ));
return 0; } ---------------------
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