Re: [Boost-users] [iterators ]bug?

Subject: Re: [Boost-users] [iterators ]bug?
From: David Abrahams (dave_at_[hidden])
Date: 2009-03-04 15:01:25

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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>

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com