std::ranges::viewable_range
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>) ||
(!ranges::view<std::remove_cvref_t<T>> &&
(std::is_lvalue_reference_v<T> ||
(std::movable<std::remove_reference_t<T>> && !/*is-initializer-list*/<T>))));
| (since C++20) |
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
#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;
});
}
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 |
See also
|
(C++20) | a view that includes all elements of a range(alias template) (range adaptor object) |
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https://en.cppreference.com/cpp/ranges/viewable_range
