constexpr iterator(chunk_by_view& parent, iterator_t<V> current, iterator_t<V> next);
constexpr value_type operator*() const;
constexpr iterator& operator++();
constexpr iterator operator++(int);
constexpr iterator& operator--() requires bidirectional_range<V>;
constexpr iterator operator--(int) requires bidirectional_range<V>;
friend constexpr bool operator==(const iterator& x, const iterator& y);
friend constexpr bool operator==(const iterator& x, default_sentinel_t);