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std::ranges...ewable_range(3) C++ Standard Libarystd::ranges...ewable_range(3) NAME std::ranges::viewable_range - std::ranges::viewable_range Synopsis Defined in header <ranges> template< class T > concept viewable_range = ranges::range<T> && ((ranges::view<std::remove_cvref_t<T>> && std::constructible_from<std::remove_cvref_t<T>, T>) || (since C++20) (!ranges::view<std::remove_cvref_t<T>> && (std::is_lvalue_reference_v<T> || (std::movable<std::remove_reference_t<T>> && !/*is-initializer-list*/<T>)))); The viewable_range concept is a refinement of range that describes a range that can be converted into a view through views::all. The constant /*is-initializer-list*/<T> is true if and only if std::remove_cvref_t<T> is a specialization of std::initializer_list. Example // Run this code #include <ranges> #include <string> #include <vector> struct valid_result {}; struct invalid_result {}; template <typename T> concept valid_viewable_range = std::same_as<T, valid_result>; template <typename T> concept invalid_viewable_range = std::same_as<T, invalid_result>; auto test_viewable_range(std::ranges::viewable_range auto &&) -> valid_result; auto test_viewable_range(auto&&) -> invalid_result; int main() { auto il = {1, 2, 3}; int arr []{1, 2, 3}; std::vector vec{1, 2, 3}; std::ranges::ref_view r{arr}; std::ranges::owning_view o{std::string("Hello")}; static_assert(requires { { test_viewable_range(il) } -> valid_viewable_range; { test_viewable_range(std::move(il)) } -> invalid_view- able_range; { test_viewable_range(arr) } -> valid_viewable_range; { test_viewable_range(std::move(arr)) } -> invalid_view- able_range; { test_viewable_range(vec) } -> valid_viewable_range; { test_viewable_range(std::move(vec)) } -> valid_view- able_range; { test_viewable_range(r) } -> valid_viewable_range; { test_viewable_range(std::move(r)) } -> valid_viewable_range; { test_viewable_range(o) } -> invalid_viewable_range; { test_viewable_range(std::move(o)) } -> valid_viewable_range; { test_viewable_range(std::ranges::ref_view(o)) } -> valid_viewable_range; }); } Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 3481 C++20 viewable_range accepted an lvalue of a rejects move-only view P2415R2 C++20 viewable_range only accepted non-view rvalues accepts more types that are borrowed_range See also views::all_t a view that includes all elements of a range views::all (alias template) (range adaptor object) (C++20) http://cppreference.com 2024.06.10 std::ranges...ewable_range(3)
NAME | Synopsis | Example | See also
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