23 General utilities library [utilities]
template <class T> struct variant_size;
Remarks:
All specializations of
variant_size shall meet the
UnaryTypeTrait requirements (
[meta.rqmts])
with a base characteristic 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
base characteristic 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).