distance.cpp

template <typename Iterator, typename IteratorType>
struct __distance {
	static typename std::iterator_traits<Iterator>::difference_type
	f(Iterator l, Iterator r) {
		typename std::iterator_traits<Iterator>::difference_type result(0);
		while (l != r) {
			++l;
			++result;
		}
		return result;
	}
};

template <typename Iterator>
struct __distance<Iterator, std::random_access_iterator_tag> {
	static typename std::iterator_traits<Iterator>::difference_type
	f(Iterator l, Iterator r) {
		return r - l;
	}
};

template <typename Iterator>
typename std::iterator_traits<Iterator>::difference_type distance(Iterator l, Iterator r) {
	return __distance<Iterator, typename std::iterator_traits<Iterator>::iterator_category>::f(l, r);
}