A side note: I think you may be able to simplify `is_compatible` by getting rid of hand-rolled `yes` and `no` constants (and subsequent manual size-testing for `value` computation) and using `std::true_type` and `std::false_type`, respectively: http://en.cppreference.com/w/cpp/types/integral_constant

Edit: noticed you're using these in another place (`compatible` implementation), so perhaps there's a reason for a different approach?