Re: [boost] [hash] Turn on BOOST_HASH_NO_IMPLICIT_CASTS by default

Stewart, Robert wrote:

You could also use std::numeric_limits<T>::is_specialized to detect a possibly larger set of types to which overloads in the details namespace could be applied.

Some stdlib implementers have chosen to provide a primary std::hash template that is SFINAEd on is_integral || is_enum. We could do the same for hash_value.