Scala has three main types of collections:
List—as you’d expect, an ordered collection of objects
Set—an unordered collection
Map—a dictionary of key-value pairs
Scala favors immutable collections, even though mutable versions are also available. If you want to modify a collection and if all the operations on the collection are all within a single thread, you can choose a mutable collection. However, if you plan to use the collection across threads or actors, the immutable collections are better. Immutable collections are thread safe, free from side effects, and help with program correctness. You can choose between these versions by selecting a class in one of these two packages: scala.collection.mutable or scala.collection.immutable ...