23 General utilities library [utilities]

23.7 Variants [variant]

23.7.12 Hash support [variant.hash]

template<class... Types> struct hash<variant<Types...>>;
The specialization hash<variant<Types...>> is enabled ([unord.hash]) if and only if every specialization in hash<remove_­const_­t<Types>>... is enabled.
The member functions are not guaranteed to be noexcept.
template<> struct hash<monostate>;
The specialization is enabled ([unord.hash]).