std::ranges::view::empty,std::ranges::empty_view (3) - Linux Manuals

std::ranges::view::empty,std::ranges::empty_view: std::ranges::view::empty,std::ranges::empty_view

NAME

std::ranges::view::empty,std::ranges::empty_view - std::ranges::view::empty,std::ranges::empty_view

Synopsis

template<class T>
requires is_object_v<T> (1) (since C++20)
class empty_view : public view_interface<empty_view<T>>
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

// Run this code

  #include <ranges>

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