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

Defined in header
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)
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.

[edit] Parameters

[edit] Return value

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

[edit] Example

#include #include #include #include   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:

[edit] 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

[edit] See also

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