operator-(std::common_iterator)

template< std::sized_sentinel_for<I> I2, std::sized_sentinel_for<I> S2 >
requires std::sized_sentinel_for<S, I2>
friend constexpr std::iter_difference_t<I2>
operator-( const common_iterator& x, const std::common_iterator<I2, S2>& y );

#include <algorithm>
#include <iostream>
#include <iterator>
 
int main()
{
    int a[]{0, 1, 2, 3, 4, 5};
 
    using CI = std::common_iterator<
                   std::counted_iterator<int*>,
                   std::default_sentinel_t
                   >;
 
    CI i1{std::counted_iterator{a + 1, 2}};
    CI i2{std::counted_iterator{a, 3}};
    CI s1{std::default_sentinel};
    CI s2{std::default_sentinel};
 
    std::cout << (s2 - s1) << ' '
              << (i2 - i1) << ' '
              << (i1 - s1) << '\n';
}