On 2020-10-05 17:41, Emile Cormier via Std-Proposals wrote:

> If C/C++ had been designed with void being an empty monostate value
> type, I guess we wouldn't have all this trouble of treating void as a
> special case in generic programming. Libraries wouldn't have needed to
> invent their own "nothing" types like nullopt_t or monostate_t.

There has been some work in that direction, but I do not know the
current state:

   https://wg21.link/p0146