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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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