Functional Programming Patterns in Scala and Clojure

Pattern 5

Replacing Iterator

Intent

To iterate through the elements of a sequence in order, without having to index into it

Overview

An iterator is an object that allows us to iterate over all the objects in a sequence. It does so by maintaining an internal bit of state that keeps track of where in the sequence the iterator is currently. At its simplest, an implementation of Iterator just requires a method that returns the next item in the sequence, with some sentinel value returned when there are no more items.

Most implementations have a separate method to check to see if the iterator has any more items, rather than using a sentinel to check. Some implementations of Iterator allow the underlying collection to be modified by removing the current ...