std::tuple_element<std::tuple>

 

C++

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rel_ops::operator!= rel_ops::operator> rel_ops::operator<= rel_ops::operator>=

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std::tuple

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ignore

 

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)
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< 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-type indexed access to the types of the elements of the tuple.

Member types

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

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

run this code

#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()
{
   type_list<int, char, bool>::type<2> x = true;
}

See also

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)