std::ranges::views::empty, std::ranges::empty_view
From cppreference.com
| Defined in header <ranges>
|
||
| template<class T> requires std::is_object_v<T> |
(1) | (since C++20) |
| namespace views { template<class T> |
(2) | (since C++20) |
1) A range factory that produces a
view of no elements of a particular type.2) Variable template for
empty_view.Member functions
| begin [static] |
returns nullptr (public static member function) |
| end [static] |
returns nullptr (public static member function) |
| data [static] |
returns nullptr (public static member function) |
| size [static] |
returns 0 (public static member function) |
| empty [static] |
returns true (public static member function) |
Inherited from std::ranges::view_interface | |
| (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>) |
| 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>) | |
returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>) | |
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>) | |
returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>) | |
std::ranges::empty_view::begin
| static constexpr T* begin() noexcept { return nullptr; } |
(since C++20) | |
empty_view does not reference any element.
std::ranges::empty_view::end
| static constexpr T* end() noexcept { return nullptr; } |
(since C++20) | |
empty_view does not reference any element.
std::ranges::empty_view::data
| static constexpr T* data() noexcept { return nullptr; } |
(since C++20) | |
empty_view does not reference any element.
std::ranges::empty_view::size
| static constexpr std::size_t size() noexcept { return 0; } |
(since C++20) | |
empty_view is always empty.
std::ranges::empty_view::empty
| static constexpr bool empty() noexcept { return true; } |
(since C++20) | |
empty_view is always empty.
Helper templates
| template<class T> constexpr bool ranges::enable_borrowed_range<ranges::empty_view<T>> = true; |
(since C++20) | |
This specialization of ranges::enable_borrowed_range makes empty_view satisfy borrowed_range.
Notes
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.
Example
Run this code
#include <ranges> int main() { namespace ranges = std::ranges; ranges::empty_view<long> e; static_assert(ranges::empty(e)); // uses operator bool static_assert(0 == e.size()); static_assert(nullptr == e.data()); static_assert(nullptr == e.begin()); static_assert(nullptr == e.end()); static_assert(nullptr == e.cbegin()); static_assert(nullptr == e.cend()); }
See also
| (C++17) |
a wrapper that may or may not hold an object (class template) |
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) |