std::tuple_element<std::tuple>

Defined in header <tuple>

template< std::size_t I, class T >
class tuple_element; /* undefined */

(1)

(since C++11)

template< std::size_t I, class... Types >
class tuple_element< I, tuple<Types...> >;

(2)

(since C++11)

Defined in header <tuple>

Defined in header <array>
Defined in header <utility>

(since C++17)
(since C++17)

template< std::size_t I, class T >
class tuple_element< I, const T > {
  typedef typename
      std::add_const<typename std::tuple_element<I, T>::type>::type type;
};

(3)

(since C++11)

template< std::size_t I, class T >
class tuple_element< I, volatile T > {
  typedef typename
      std::add_volatile<typename std::tuple_element<I, T>::type>::type type;
};

(4)

(since C++11)

template< std::size_t I, class T >
class tuple_element< I, const volatile T > {
  typedef typename
      std::add_cv<typename std::tuple_element<I, T>::type>::type type;
};

(5)

(since C++11)

Provides compile-time indexed access to the types of the elements of the tuple.

Member types

Member type	Definition
type	the type of `I`th element of the tuple, where `I` is in `[0, sizeof...(Types))`

Helper types

template <std::size_t I, class T>
using tuple_element_t = typename tuple_element<I, T>::type;

(since C++14)

Possible implementation

template< std::size_t I, class T >
struct tuple_element;
  
// recursive case
template< std::size_t I, class Head, class... Tail >
struct tuple_element<I, std::tuple<Head, Tail...>>
    : std::tuple_element<I-1, std::tuple<Tail...>> { };
  
// base case
template< class Head, class... Tail >
struct tuple_element<0, std::tuple<Head, Tail...>> {
   typedef Head type;
};

Example

#include <iostream>
#include <tuple>
  
template <class... Args>
struct type_list
{
   template <std::size_t N>
   using type = typename std::tuple_element<N, std::tuple<Args...>>::type;
};
  
int main()
{
   std::cout << std::boolalpha;
   type_list<int, char, bool>::type<2> x = true;
   std::cout << x << '\n';
}

Output:

true

std::tuple_element<std::array>	obtains the type of the elements of `array` (class template specialization)
std::tuple_element<std::pair> (C++11)	obtains the type of the elements of `pair` (class template specialization)

std::tuple_element&lt;std::tuple&gt;

Member types

Helper types

Possible implementation

Example

See also

std::tuple_element<std::tuple>