8.6. Traversing, Mapping, Filtering, Folding, and Reducing

The functional collections we just discussed—lists, maps, sets, as well as tuples and arrays—all support several common operations based on read-only traversal. In fact, this uniformity can be exploited if any “container” type also supports these operations. For example, an Option contains zero or one elements, if it is a None or Some, respectively.

8.6.1. Traversal

The standard traversal method for Scala containers is foreach, which is defined by the Iterable traits that the containers mix in. It is O(N) in the number of elements. Here is an example of its use for lists and maps: