std::ranges::view::empty, std::ranges::empty_view
template<class T>
requires is_object_v<T>
class empty_view : public view_interface<empty_view<T>>
| (1) | (since C++20) |
namespace view {
template<class T> inline constexpr empty_view<T> empty{};
}
| (2) | (since C++20) |
1) A range adaptor that produces a
View of no elements of a particular type.
2) Variable template for
empty_view.Member functions
std::ranges::empty_view::begin
static constexpr T* begin() noexcept { return nullptr; }
|
empty_view does not reference any element.
std::ranges::empty_view::end
static constexpr T* end() noexcept { return nullptr; }
|
empty_view does not reference any element.
std::ranges::empty_view::data
static constexpr T* data() noexcept { return nullptr; }
|
empty_view does not reference any element.
std::ranges::empty_view::size
static constexpr std::ptrdiff_t size() noexcept { return 0; }
|
empty_view is always empty.
std::ranges::empty_view::empty
static constexpr bool empty() noexcept { return true; }
|
empty_view is always empty.
Non-member functions
begin, end(std::ranges::empty_view)
friend constexpr T* begin(empty_view) noexcept { return nullptr; }
| (1) | |
friend constexpr T* end(empty_view) noexcept { return nullptr; }
| (2) |
These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::ranges::empty_view<T> is an associated class of the arguments.
Example
#include <ranges>
int main()
{
std::ranges::empty_view<int> e;
static_assert(std::ranges::empty(e));
static_assert(0 == e.size());
}
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