NAME¶

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

Synopsis¶

Defined in header <ranges>
template<class T>

requires std::is_object_v<T> (1) (since C++20)

class empty_view : public ranges::view_interface<empty_view<T>>
namespace views {

template<class T> inline constexpr empty_view<T> empty{}; (2) (since C++20)

}

1) A range factory that produces a view of no elements of a particular type.
2) Variable template for empty_view.

Member functions¶

begin returns nullptr
[static] (C++20) (public static member function)
end returns nullptr
[static] (C++20) (public static member function)
data returns nullptr
[static] (C++20) (public static member function)
size returns 0 (zero)
[static] (C++20) (public static member function)
empty returns true
[static] (C++20) (public static member function)
Inherited from std::ranges::view_interface
operator bool Returns whether the derived view is not empty. Provided if
(C++20) ranges::empty is applicable to it.
(public member function of std::ranges::view_interface<D>)
front Returns the first element in the derived view. Provided if it
(C++20) satisfies forward_range.
(public member function of std::ranges::view_interface<D>)
back Returns the last element in the derived view. Provided if it
(C++20) satisfies bidirectional_range and common_range.
(public member function of std::ranges::view_interface<D>)
operator[] Returns the nth element in the derived view. Provided if it
(C++20) satisfies random_access_range.
(public member function of std::ranges::view_interface<D>)

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.

Helper templates

template<class T>
inline constexpr bool enable_borrowed_range<ranges::empty_view<T>> = (since C++20)
true;

This specialization of std::ranges::enable_borrowed_range makes empty_view satisfy
borrowed_range.

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.

Example¶

// Run this code

#include <ranges>

int main()
{
std::ranges::empty_view<long> e;
static_assert(std::ranges::empty(e));
static_assert(0 == e.size());
static_assert(nullptr == e.data());
static_assert(nullptr == e.begin());
static_assert(nullptr == e.end());
}

See also¶

ranges::single_view a view that contains a single element of a specified value
views::single (class template) (customization point object)
(C++20)
views::all_t a view that includes all elements of a range
views::all (alias template) (range adaptor object)
(C++20)
ranges::ref_view a view of the elements of some other range
(C++20) (class template)