View source for cpp/ranges/subrange/tuple size

{{cpp/title|tuple_size<small><std:ranges::subrange></small>}}
{{cpp/ranges/subrange/navbar}}
{{ddcl|header=ranges|since=c++20|
template< class I, class S, ranges::subrange_kind K >
struct tuple_size<ranges::subrange<I, S, K>>
    : std::integral_constant<std::size_t, 2> {};
}}

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

{{cpp/types/integral_constant/inherit2|the constant value 2|std::size_t}}

===Example===
{{example
|code=
#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";
}
|output=
sub_a1: { 1 2 3 4 5 }
sub_a2 size = 3
sub_a2: { 2 3 4 }
}}

===See also===
{{dsc begin}}
{{dsc inc|cpp/language/dsc structured binding}}
{{dsc inc|cpp/utility/dsc tuple_size}}
{{dsc inc|cpp/utility/tuple/dsc tuple_size}}
{{dsc inc|cpp/utility/pair/dsc tuple_size}}
{{dsc inc|cpp/container/array/dsc tuple_size}}
{{dsc inc|cpp/ranges/subrange/dsc tuple_element}}
{{dsc end}}

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