std::tuple_size<std:ranges::subrange>

Since C++20

Header: <ranges>

The partial specialization of std::tuple_size for std::ranges::subrange provides a compile-time way to obtain the number of components of a subrange, which is always 2, using tuple-like syntax. It is provided for structured binding support.

# Declarations

template< class I, class S, ranges::subrange_kind K >
struct tuple_size<ranges::subrange<I, S, K>>
: std::integral_constant<std::size_t, 2> {};

(since C++20)

# Example

#include <array>
#include <iostream>
#include <iterator>
#include <ranges>
 
int main()
{
    static_assert(2 == std::tuple_size_v<std::ranges::subrange<int*, int*>>);
 
    using array5 = std::array<int, 5>;
 
    static_assert(2 == std::tuple_size<std::ranges::subrange<
        array5::const_iterator, array5::const_iterator>>{});
 
    constexpr array5 a{1, 2, 3, 4, 5};
 
    std::ranges::subrange sub_a1{a};
 
    for (std::cout << "sub_a1: { "; int e : sub_a1)
        std::cout << e << ' ';
    std::cout << "}\n";
 
    std::ranges::subrange sub_a2{std::next(cbegin(a)), std::prev(cend(a))};
 
    const auto [first, last] = sub_a2;
    std::cout << "sub_a2 size = " << std::distance(first, last) << '\n';
 
    for (std::cout << "sub_a2: { "; int e : sub_a2)
        std::cout << e << ' ';
    std::cout << "}\n";
}

# See also