std::ranges::views::empty, std::ranges::empty_view - cppreference.com (original) (raw)
| Defined in header | ||
|---|---|---|
| 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> constexpr empty_view<T> empty{}; } | (2) | (since C++20) |
A range factory that produces a view of no elements of a particular type.
Variable template for
empty_view.
Contents
- 1 Member functions
- 2 std::ranges::empty_view::begin
- 3 std::ranges::empty_view::end
- 4 std::ranges::empty_view::data
- 5 std::ranges::empty_view::size
- 6 std::ranges::empty_view::empty
[edit] 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 | |
| cbegin(C++23) | returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface) [edit] |
| cend(C++23) | returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface) [edit] |
| operator bool | returns whether the derived view is not empty, provided only if ranges::empty is applicable to it (public member function of std::ranges::view_interface) [edit] |
| front | returns the first element in the derived view, provided if it satisfies forward_range (public member function of std::ranges::view_interface) [edit] |
| back | returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range (public member function of std::ranges::view_interface) [edit] |
| operator[] | returns the nth element in the derived view, provided only if it satisfies random_access_range (public member function of std::ranges::view_interface) [edit] |
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.
[edit] Helper templates
This specialization of ranges::enable_borrowed_range makes empty_view satisfy borrowed_range.
[edit] 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.
[edit] Example
#include int main() { namespace ranges = std::ranges; ranges::empty_view 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()); }