Iterator

The Iterator design pattern introduces an external object that allows to go through the items of collections without knowing the internal structure of the collections. This is one of the most popular pattern, and you can find it implemented in standard libraries of almost all programming languages. Sometimes, it's called Enumerator instead of Iterator.

Motivation

Today's programming languages often provide rich variety of collections, i.e., arrays, lists, dictionaries (hashmap), but also e.g. trees. Sometimes, it's useful to implement our own collection, especially if it's supposed to provide some special operations over its elements. At some point, we need to iterate through every collection, i.e. to go through all its elements from the first to the last one and print them, for example. If each collection implemented its own interface to iterate over its elements, first, we'd have to examine them, and collections are sometimes really complicated. And second, the language itself won't be able to support syntactic sugar such as the foreach loop. If you think of introducing some general interface the

...End of the preview...
Continue further