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

Since C++20

Header: <ranges>

  1. A range factory that produces a view of no elements of a particular type.

# Declarations

template<class T>
requires std::is_object_v<T>
class empty_view : public ranges::view_interface<empty_view<T>>

(since C++20)

namespace views {
template<class T>
constexpr empty_view<T> empty{};
}

(since C++20)

# 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

#include <ranges>
 
int main()
{
    namespace ranges = std::ranges;
 
    ranges::empty_view<long> e;
    static_assert(ranges::empty(e)); // uses operator bool
    static_assert(0 == e.size());
    static_assert(nullptr == e.data());
    static_assert(nullptr == e.begin());
    static_assert(nullptr == e.end());
    static_assert(nullptr == e.cbegin());
    static_assert(nullptr == e.cend());
}

# See also