operator==,<=>(std::counted_iterator)

Since C++20

Compares the underlying lengths (i.e. distances to the end).

# Declarations

template< std::common_with<I> I2 >
friend constexpr bool operator==(
const counted_iterator& x, const counted_iterator<I2>& y );

(since C++20)

template< std::common_with<I> I2 >
friend constexpr strong_ordering operator<=>(
const counted_iterator& x, const counted_iterator<I2>& y );

(since C++20)

# Parameters

# Notes

Since the length counts down, not up, the order of the arguments of operator<=> in the underlying comparison expression is reversed, i.e. y is lhs, x is rhs.

# Example

#include <initializer_list>
#include <iterator>
 
int main()
{
    static constexpr auto v = {1, 2, 3, 4, 5, 6};
    constexpr std::counted_iterator<std::initializer_list<int>::iterator>
        it1{v.begin(), 5},
        it2{v.begin(), 5},
        it3{v.begin() + 1, 4},
        it4{v.begin(), 0};
    static_assert(it1 == it2);
    static_assert(it2 != it3);
    static_assert(it2 <  it3);
    static_assert(it1 <= it2);
    static_assert(it3 != std::default_sentinel);
    static_assert(it4 == std::default_sentinel);
 
//  it2 == std::counted_iterator{v.begin(), 4}; // UB: operands do not refer to
                                                // elements of the same sequence
}

# See also