Fwiw, I used something closely related in libc++ for SFINAE on the “member template members” of the containers (the ones taking iterators) to disambiguate them from the members/constructors not taking iterators, but having the same number of parameters. But instead of is_iterator, I needed is_input_iterator, is_forward_iterator, etc. These refinements are implemented similar to what Beman shows, but takes into account which std iterator tag the nested iterator_category type is implicitly convertible to.
I actually have used a `has_iterator_traversal` trait to check iterator
traversal, like this:
template