Defined in header <ranges> | ||
|---|---|---|
template<class T>
requires std::is_object_v<T>
class empty_view : public ranges::view_interface<empty_view<T>>
| (1) | (since C++20) |
namespace views {
template<class T> inline constexpr empty_view<T> empty{};
}
| (2) | (since C++20) |
view of no elements of a particular type.empty_view.| begin
[static] (C++20) | returns nullptr (public static member function) |
| end
[static] (C++20) | returns nullptr (public static member function) |
| data
[static] (C++20) | returns nullptr (public static member function) |
| size
[static] (C++20) | returns 0 (zero) (public static member function) |
| empty
[static] (C++20) | returns true (public static member function) |
Inherited from |
|
|
(C++23) | returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>) |
|
(C++23) | returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function of std::ranges::view_interface<D>) |
|
(C++20) | returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>) |
static constexpr T* begin() noexcept { return nullptr; }
| (since C++20) |
empty_view does not reference any element.
static constexpr T* end() noexcept { return nullptr; }
| (since C++20) |
empty_view does not reference any element.
static constexpr T* data() noexcept { return nullptr; }
| (since C++20) |
empty_view does not reference any element.
static constexpr std::size_t size() noexcept { return 0; }
| (since C++20) |
empty_view is always empty.
static constexpr bool empty() noexcept { return true; }
| (since C++20) |
empty_view is always empty.
template<class T> inline constexpr bool enable_borrowed_range<ranges::empty_view<T>> = true; | (since C++20) |
This specialization of std::ranges::enable_borrowed_range makes empty_view satisfy borrowed_range.
Although empty_view obtains front, back, and operator[] member functions from view_interface, calls to them always result in undefined behavior since an empty_view is always empty.
The inherited operator bool conversion function always returns false.
#include <ranges>
int main()
{
std::ranges::empty_view<long> e;
static_assert(std::ranges::empty(e));
static_assert(0 == e.size());
static_assert(nullptr == e.data());
static_assert(nullptr == e.begin());
static_assert(nullptr == e.end());
}|
(C++20) | a view that contains a single element of a specified value (class template) (customization point object) |
|
(C++20) | a view that includes all elements of a range (alias template) (range adaptor object) |
|
(C++20) | a view of the elements of some other range (class template) |
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https://en.cppreference.com/w/cpp/ranges/empty_view