std::ranges::viewable_range
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C++
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Defined in header
<ranges>
template< class T >
(since C++20)
concept viewable_range =
ranges::range <T> &&
((ranges::view <std::remove_cvref_t <T>> &&
std::constructible_from <std::remove_cvref_t <T>, T>) ||
(!ranges::view <std::remove_cvref_t <T>> &&
(std::is_lvalue_reference_v <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 .
[edit] 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_viewable_range; { test_viewable_range(arr) } -> valid_viewable_range; { test_viewable_range(std::move(arr)) } -> invalid_viewable_range; { test_viewable_range(vec) } -> valid_viewable_range; { test_viewable_range(std::move(vec)) } -> valid_viewable_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; }); }
[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 3481 | C++20 | viewable_range accepted an lvalue of a move-only view
|
rejects |
| P2415R2 | C++20 | viewable_range only accepted non-view rvalues that are borrowed_range
|
accepts more types |