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std::ranges::get(std::ranges::subrange) - cppreference.com

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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

Return value

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

Example

#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:

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[edit]
tuple accesses specified element
(function template) [edit]
accesses an element of a pair
(function template) [edit]
accesses an element of an array
(function template) [edit]
reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template) [edit]
obtains a reference to real or imaginary part from a std::complex
(function template) [edit]