std::tuple_element<std::ranges::subrange>

Defined in header <ranges> 
template< class I, class S, ranges::subrange_kind K >
struct tuple_element<0, ranges::subrange<I, S, K>>;
 (1) (since C++20) 
template< class I, class S, ranges::subrange_kind K >
struct tuple_element<0, const ranges::subrange<I, S, K>>;
 (2) (since C++20) 
template< class I, class S, ranges::subrange_kind K >
struct tuple_element<1, ranges::subrange<I, S, K>>;
 (3) (since C++20) 
template< class I, class S, ranges::subrange_kind K >
struct tuple_element<1, const ranges::subrange<I, S, K>>;
 (4) (since C++20)

The partial specializations of std::tuple_element for std::ranges::subrange provide compile-time access to the iterator or sentinel type of a subrange, using tuple-like syntax. They are provided for structured binding support.

1,2) Obtains the iterator type, i.e. I.
3,4) Obtains the sentinel type, i.e. S.

Member types

Member type Definition
type (1,2) I
(3,4) S

Notes

As get functions for subrange return iterators and sentinels by value, const qualifier is not added to the result types when the subrange is const-qualified (but not volatile-qualified).

If the subrange is volatile-qualified, the result types are also volatile-qualified because the partial specialization for volatile or const volatile types are used. Such usage is deprecated.

Example

#include <iterator>
#include <list>
#include <ranges>
#include <type_traits>
 
int main()
{
    std::list<int> list{3, 1, 4, 1, 5, 9, 2, 6};
 
    std::ranges::subrange subrange
    {
        std::counted_iterator{std::begin(list), 4},
        std::default_sentinel
    };
 
    static_assert(
        std::is_same_v<
            std::tuple_element_t<0, decltype(subrange)>,
            // implementation-defined type:
            std::counted_iterator<std::_List_iterator<int>>
            >);
 
    static_assert(
        std::is_same_v<
            std::tuple_element_t<1, decltype(subrange)>,
            std::default_sentinel_t
            >);
}

See also

Structured binding (C++17) binds the specified names to sub-objects or tuple elements of the initializer
(C++11)
 obtains the element types of a tuple-like type
(class template)
(C++20)
 obtains the number of components of a std::ranges::subrange
(class template specialization)

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