std::ranges::get(std::ranges::subrange)
From cppreference.com
| 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 |