"David Abrahams" <dave@boost-consulting.com> wrote in message news:ulkqccd9c.fsf@boost-consulting.com...
I see no requirement that a `tag' type member be included in http://boost.org/libs/mpl/doc/refmanual/integral-constant.html. However, it does look like the current implementation of equal_to depends on the presence of `tag'. I'm not sure what the plan was here; Aleksey?
It would be easy enough to make most of the MPL numeric metafunctions work on types that don't supply `tag'.
The larger problem (potentially) is that boost::integral_constant which is used by a lot of type_traits metafunctions does have the tag memeber(because its derived from mpl::integral_c), but it doesnt advertise it in its documentation. It would be interesting to try a version of boost::integral_constant which matches the std::integral_constant requirements and no more and see what if any problems it causes, particularly for code that uses mpl, to see what problems might be caused by replacing boost::integral_constant with std::integral_constant. Of course I may be making a fuss out of nothing, but to me it looks like this issue could cause a lot of problems. Also perhaps boost::integral-constant (the type_traits version) should then be changed to implement only the requirements of the std::integral_constant... IOW not derive from mpl::integral_c ? regards Andy Little