3.6 KiB
[tuple.elem]
22 General utilities library [utilities]
22.4 Tuples [tuple]
22.4.8 Element access [tuple.elem]
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; // #1 template<size_t I, class... Types> constexpr const tuple_element_t<I, tuple<Types...>>& get(const tuple<Types...>& t) noexcept; // #2 template<size_t I, class... Types> constexpr const tuple_element_t<I, tuple<Types...>>&& get(const tuple<Types...>&& t) noexcept;
Mandates: I < sizeof...(Types).
Returns: A reference to the Ith element of t, where indexing is zero-based.
[Note 1:
For the overload marked #1, if a type 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&&.
â end note]
[Note 2:
Constness is shallow.
For the overload marked #2, if a type 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 non-static data members of reference type.
â 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;
Mandates: The type T occurs exactly once in Types.
Returns: A reference to the element of t corresponding to the typeT in Types.
[Example 1: const tuple<int, const int, double, double> t(1, 2, 3.4, 5.6);const int& i1 = get(t); // OK, i1 has value 1const int& i2 = get(t); // OK, i2 has value 2const double& d = get(t); // error: type double is not unique within t â end example]
[Note 3:
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.
â end note]