std::ranges:: get (std::ranges::subrange)

From cppreference.com
C++
Ranges library
Range adaptors
std::ranges::subrange
Defined in header <ranges>
template < std:: size_t N, class I, class S, ranges:: subrange_kind K >

requires ( ( N == 0 && std:: copyable < I > ) || N == 1 )

constexpr auto get ( const ranges:: subrange < I, S, K > & r ) ;
(1) (since C++20)
template < std:: size_t N, class I, class S, ranges:: subrange_kind K >

requires ( N < 2 )

constexpr auto get ( ranges:: subrange < I, S, K > && r ) ;
(2) (since C++20)
namespace std { using ranges :: get ; }
(3) (since C++20)

Provides structured binding support.

1) Obtains the iterator or sentinel from a subrange lvalue (or a const rvalue) when N == 0 or N == 1 , respectively.
2) Same as (1) , except that it takes a non-const subrange rvalue.
3) Overloads (1,2) are imported into namespace std , which simplifies their usage and makes every subrange with a copyable iterator a pair-like type.

Parameters

r - a subrange

Return value

1,2) If N is ​ 0 ​ , returns r. begin ( ) . Otherwise ( N is 1 ), returns r. end ( ) .

Example

Run this code 
#include <array>
#include <iostream>
#include <iterator>
#include <ranges>
 
int main()
{
    std::array a{1, -2, 3, -4};
 
    std::ranges::subrange sub_a{std::next(a.begin()), std::prev(a.end())};
    std::cout << *std::ranges::get<0>(sub_a) << ' '   // == *(begin(a) + 1)
              << *std::ranges::get<1>(sub_a) << '\n'; // == *(end(a) - 1)
 
    *std::get<0>(sub_a) = 42; // OK
//  *std::get<2>(sub_a) = 13; // Error: index can only be 0 or 1
}

Output: 

-2 -4

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3589 C++20 overload ( 1 ) copies begin_ if N is ​ 0 ​ , but I might not model copyable added constraints

See also

Structured binding (C++17) binds the specified names to sub-objects or tuple elements of the initializer
(C++11)
tuple accesses specified element
(function template)
(C++11)
accesses an element of a pair
(function template)
(C++11)
accesses an element of an array
(function template)
(C++17)
reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template)
(C++26)
obtains a reference to real or imaginary part from a std::complex
(function template)
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