template <class T> struct variant_size;
Remarks: All specializations of variant_size<T> shall meet the UnaryTypeTrait requirements ([meta.rqmts]) with a BaseCharacteristic of integral_constant<size_t, N> for some N.
template <class T> class variant_size<const T>;
template <class T> class variant_size<volatile T>;
template <class T> class variant_size<const volatile T>;
Let VS denote variant_size<T> of the cv-unqualified type T. Then each of the three templates shall meet the UnaryTypeTrait requirements ([meta.rqmts]) with a BaseCharacteristic of integral_constant<size_t, VS::value>.
template <class... Types>
struct variant_size<variant<Types...>>
: integral_constant<size_t, sizeof...(Types)> { };
template <size_t I, class T> class variant_alternative<I, const T>;
template <size_t I, class T> class variant_alternative<I, volatile T>;
template <size_t I, class T> class variant_alternative<I, const volatile T>;
Let VA denote variant_alternative<I, T> of the cv-unqualified type T. Then each of the three templates shall meet the TransformationTrait requirements ([meta.rqmts]) with a member typedef type that names the following type:
for the first specialization, add_const_t<VA::type>,
for the second specialization, add_volatile_t<VA::type>, and
for the third specialization, add_cv_t<VA::type>.
variant_alternative<I, variant<Types...>>::type
Requires: I < sizeof...(Types).
Value: The type TI.