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std::tuple_element<std::tuple>

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< cpp‎ | utility‎ | tuple
Revision as of 16:55, 1 July 2013 by P12bot (Talk | contribs)

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.

Contents

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

#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

obtains the type of the elements of array
(class template specialization) [edit]
obtains the type of the elements of pair
(class template specialization) [edit]