std::ranges::constant_range
From cppreference.com
C++
Ranges library
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Range primitives | |||||||
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Range concepts | |||||||||||||||||||
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Range adaptors | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Defined in header <ranges>
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template
<
class T >
concept constant_range =
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(1) | (since C++23) |
Helper concepts |
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template
<
class T >
concept /*constant-iterator*/
=
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(2) | (exposition only*) |
1) The
constant_range
concept is a refinement of range
for which ranges::begin
returns a constant iterator
2) The concept
/*constant-iterator*/
<T>
Example
Run this code
#include <ranges> #include <span> #include <string_view> #include <vector> // mechanisms for ensuring the parameter is a constant range // 1) an overload set where the mutable one defers to the constant one template<std::ranges::constant_range R> void takes_any_range1(R&& r) { // R is definitely a constant range } template<std::ranges::range R> void takes_any_range1(R&& r) { takes_any_range1(std::views::as_const(std::forward<R>(r))); } // 2) one function template that shadows its parameter template<std::ranges::range R> void takes_any_range2(R&& _r) { auto r = std::views::as_const(std::forward<R>(_r)); // r is definitely a constant range // never use _r again } // 3) one function template that recursively invokes itself template<std::ranges::range R> void takes_any_range3(R&& r) { if constexpr (std::ranges::constant_range<R>) { // R is definitely a constant range // put implementation here } else takes_any_range3(std::views::as_const(std::forward<R>(r))); } static_assert ( std::ranges::constant_range<const std::vector<int>> and not std::ranges::constant_range<std::vector<int>> and std::ranges::constant_range<std::string_view> and not std::ranges::constant_range<std::span<int>> and std::ranges::constant_range<std::span<const int>> and not std::ranges::constant_range<const std::span<int>> ); int main() {}