| Defined in header <utility> | ||
|---|---|---|
template< class T1, class T2 > struct tuple_element<0, std::pair<T1,T2> >; | (1) | (since C++11) |
template< class T1, class T2 > struct tuple_element<1, std::pair<T1,T2> >; | (2) | (since C++11) |
The partial specializations of std::tuple_element for pairs provide compile-time access to the types of the pair's elements, using tuple-like syntax.
Member types
First version | |
| Member type | Definition |
|---|---|
type | T1 |
Second version | |
| Member type | Definition |
type | T2 |
Possible implementation
template<std::size_t I, typename T>
struct tuple_element;
template<typename T1, typename T2>
struct tuple_element<0, std::pair<T1,T2> >
{
using type = T1;
};
template<typename T1, typename T2>
struct tuple_element<1, std::pair<T1,T2> >
{
using type = T2;
}; |
Example
#include <tuple>
#include <iostream>
#include <string>
template <int N, typename T, typename U>
static auto constexpr get(std::pair<T, U> const& pair)
-> typename std::tuple_element<N, decltype(pair)>::type
{
return N == 0 ? pair.first : pair.second;
}
int main()
{
auto var = std::make_pair(1, std::string{"one"});
std::cout << get<0>(var) << " = " << get<1>(var);
}Output:
1 = one
See also
| obtains the type of the specified element (class template specialization) | |
obtains the type of the elements of array (class template specialization) | |
| (C++11) | obtains the size of a pair (class template specialization) |
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