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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