id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
8023	Error using iterator traits with coroutine iterator	Nathan Ridge	olli	"I am getting compiler errors when using std::iterator_traits with a coroutine's iterator type:

{{{

#include <boost/coroutine/coroutine.hpp>
#include <boost/iterator/iterator_traits.hpp>

typedef boost::coroutines::coroutine<int()> coroutine_type;
typedef std::iterator_traits<coroutine_type::iterator>::pointer pointer;
}}}

The errors are (with gcc 4.7.2):


{{{

In file included from boost/boost/coroutine/coroutine.hpp:31:0,
                 from test.cpp:1:
boost/boost/coroutine/detail/coroutine_op.hpp: In instantiation of 'class boost::coroutines::detail::coroutine_op<int(), boost::coroutines::coroutine<int()>, int, 0>::iterator':
c++/bits/stl_iterator_base_types.h:143:1:   recursively required from 'constexpr const bool std::__has_iterator_category_helper<boost::coroutines::detail::coroutine_op<int(), boost::coroutines::coroutine<int()>, int, 0>::iterator>::value'
c++/bits/stl_iterator_base_types.h:143:1:   required from 'struct std::__has_iterator_category<boost::coroutines::detail::coroutine_op<int(), boost::coroutines::coroutine<int()>, int, 0>::iterator>'
c++/bits/stl_iterator_base_types.h:160:12:   required from 'struct std::iterator_traits<boost::coroutines::detail::coroutine_op<int(), boost::coroutines::coroutine<int()>, int, 0>::iterator>'
test.cpp:5:55:   required from here
boost/boost/coroutine/detail/coroutine_op.hpp:84:73: error: no type named 'pointer' in 'struct std::iterator_traits<boost::coroutines::detail::coroutine_op<int(), boost::coroutines::coroutine<int()>, int, 0>::iterator>'
boost/boost/coroutine/detail/coroutine_op.hpp:85:73: error: no type named 'reference' in 'struct std::iterator_traits<boost::coroutines::detail::coroutine_op<int(), boost::coroutines::coroutine<int()>, int, 0>::iterator>'
}}}

The problem is the following typedefs in the iterator class:

{{{

typedef typename std::iterator_traits< iterator >::pointer      pointer_t;
typedef typename std::iterator_traits< iterator >::reference    reference_t;
}}}

If the iterator class is instantiated in the context of instantiating iterator_traits<iterator>, as is the case in my example code, these typedefs cause a recursive instantiation of iterator_traits<iterator>. In the recursive instantiation, 'iterator' is incomplete, and thus does not have the required members.

A solution is to express the underlying type of these typedefs more directly, for example:

{{{

typedef typename iterator::pointer      pointer_t;
typedef typename iterator::reference    reference_t;
}}}

The coroutine's const_iterator has a similar problem.

Attached is a patch with the above fix.

"	Bugs	closed	To Be Determined	coroutine	Boost Development Trunk	Problem	fixed