Let’s revisit the Iterator pattern. “Iterator” is one of design patterns in object-oriented programming (OOP). Needless to say, extremely famous Gang of Four (Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides) are creators. As in the Wikipedia’s Iterator pattern, the iterator pattern is used when traversing container without knowing how the container works. It is OOP’s favorite pattern to “decouple” the iterator from container.