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

From cppreference.com
C++
Ranges library
Range adaptors
std::ranges::subrange
Defined in header <ranges>
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)

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.

Inherited from std:: integral_constant

Member constants

value
[static]
the constant value 2
(public static member constant)

Member functions

operator std::size_t
converts the object to std:: size_t , returns value
(public member function)
operator()
(C++14)
returns value
(public member function)

Member types

Type Definition
value_type std:: size_t
type std:: integral_constant < std:: size_t , value >

Example

Run this 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

Structured binding (C++17) binds the specified names to sub-objects or tuple elements of the initializer
(C++11)
obtains the number of elements of a tuple-like type
(class template)
(C++11)
obtains the size of

a tuple
(class template specialization)

(C++11)
obtains the size of a pair
(class template specialization)
(C++11)
obtains the size of an array
(class template specialization)
(C++20)
obtains the type of the iterator or the sentinel of a std::ranges::subrange
(class template specialization)
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