template <class T> struct tuple_size;
Remarks: All specializations of tuple_size shall meet the UnaryTypeTrait requirements with a base characteristic of integral_constant<size_t, N> for some N.
template <class... Types>
class tuple_size<tuple<Types...>> : public integral_constant<size_t, sizeof...(Types)> { };
template <size_t I, class... Types>
class tuple_element<I, tuple<Types...>> {
public:
using type = TI;
};
template <class T> class tuple_size<const T>;
template <class T> class tuple_size<volatile T>;
template <class T> class tuple_size<const volatile T>;
Let TS denote tuple_size<T> of the cv-unqualified type T. If the expression TS::value is well-formed when treated as an unevaluated operand, then each of the three templates shall meet the UnaryTypeTrait requirements with a base characteristic of
integral_constant<size_t, TS::value>Otherwise, they shall have no member value.
Access checking is performed as if in a context unrelated to TS and T. Only the validity of the immediate context of the expression is considered. [ Note: The compilation of the expression can result in side effects such as the instantiation of class template specializations and function template specializations, the generation of implicitly-defined functions, and so on. Such side effects are not in the “immediate context” and can result in the program being ill-formed. — end note ]
In addition to being available via inclusion of the <tuple> header, the three templates are available when either of the headers <array> or <utility> are included.
template <size_t I, class T> class tuple_element<I, const T>;
template <size_t I, class T> class tuple_element<I, volatile T>;
template <size_t I, class T> class tuple_element<I, const volatile T>;
Let TE denote tuple_element_t<I, T> of the cv-unqualified type T. Then each of the three templates shall meet the TransformationTrait requirements with a member typedef type that names the following type:
for the first specialization, add_const_t<TE>,
for the second specialization, add_volatile_t<TE>, and
for the third specialization, add_cv_t<TE>.