std::ranges::constant_range
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C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Ranges library
(C++23)(C++23)
(C++26)(C++26)
(C++23)(C++23)
(C++26)(C++26)
(C++26)(C++26)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
Defined in header
<ranges>
template< class T >
(1)
(since C++23)
concept constant_range =
ranges::input_range <T> &&
Helper concepts
template< class T >
(2)
(exposition only*)
concept /*constant-iterator*/ =
std::input_iterator <T> &&
1) The
constant_range concept is a refinement of range for which ranges::begin returns a constant iterator.2) The concept /*constant-iterator*/<T> is satisfied when the result of the indirection operation of the input iterator is its const reference type which implies read-only.
[edit] 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() {}