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std::ranges::views::empty, std::ranges::empty_view

From cppreference.com
< cpp‎ | ranges
 
 
 
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> 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.

Contents

[edit] 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::size_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.

[edit] 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.

[edit] Example

#include <ranges>
 
int main()
{
    std::ranges::empty_view<int> e;
    static_assert(std::ranges::empty(e));
    static_assert(0 == e.size());
}