Hi, I think non-intrusive customization way needs four specializations; 'X', 'const X', 'volatile X' and 'const volatile X'. At last, twenty specializations are required for five metafunctions. I view that's something like the pitfall of public virtual interfaces. Only range_result_iterator happens to work around by using remove_cv. See: I added followings to <libs/range/doc/example.cpp>: template< class Range > typename boost::range_result_iterator<Range>::type my_begin(Range& rng) { return boost::begin(rng); } // then... my_begin(cpair); // error Why not something like: template< class T > struct range_result_iterator : mpl::eval_if< is_const<T>, range_const_iterator< typename remove_cv<T>::type >, range_iterator< typename remove_cv<T>::type > > { }; Regards, MB p-stade.sourceforge.net