The Scala collections library involves many classes and traits.The main trait is
Iterable, which is the supertrait of both mutable and immutable
variations of sequences (
Seqs), sets,
and maps.
Sequences are ordered collections, such as Arrays and Lists. Sets contain at most
one of each object, as determined by the
== method. Maps contain a collection of keys mapped to values.
All collections are called as immutable by default, to call mutable type you should use
scala.collection.mutable package where it is allowed.