template <size_t I, class... Types>
constexpr tuple_element_t<I, tuple<Types...>>&
get(tuple<Types...>& t) noexcept;
template <size_t I, class... Types>
constexpr tuple_element_t<I, tuple<Types...>>&&
get(tuple<Types...>&& t) noexcept; // Note A
template <size_t I, class... Types>
constexpr const tuple_element_t<I, tuple<Types...>>&
get(const tuple<Types...>& t) noexcept; // Note B
template <size_t I, class... Types>
constexpr const tuple_element_t<I, tuple<Types...>>&& get(const tuple<Types...>&& t) noexcept;
Requires: I < sizeof...(Types). The program is ill-formed if I is out of bounds.
Returns: A reference to the Ith element of t, where indexing is zero-based.
[ Note A: If a T in Types is some reference type X&, the return type is X&, not X&&. However, if the element type is a non-reference type T, the return type is T&&. — end note ]
[ Note B: Constness is shallow. If a T in Types is some reference type X&, the return type is X&, not const X&. However, if the element type is a non-reference type T, the return type is const T&. This is consistent with how constness is defined to work for member variables of reference type. — end note ]
template <class T, class... Types>
constexpr T& get(tuple<Types...>& t) noexcept;
template <class T, class... Types>
constexpr T&& get(tuple<Types...>&& t) noexcept;
template <class T, class... Types>
constexpr const T& get(const tuple<Types...>& t) noexcept;
template <class T, class... Types>
constexpr const T&& get(const tuple<Types...>&& t) noexcept;
Requires: The type T occurs exactly once in Types.... Otherwise, the program is ill-formed.
Returns: A reference to the element of t corresponding to the type T in Types....
[ Example:
const tuple<int, const int, double, double> t(1, 2, 3.4, 5.6); const int& i1 = get<int>(t); // OK. Not ambiguous. i1 == 1 const int& i2 = get<const int>(t); // OK. Not ambiguous. i2 == 2 const double& d = get<double>(t); // ERROR. ill-formed
— end example ]
[ Note: The reason get is a non-member function is that if this functionality had been provided as a member function, code where the type depended on a template parameter would have required using the template keyword. — end note ]