Commonly used collections in Scala

Let's start  by discussing a few immutable concrete collections.

List

A list is a linear sequence and can be defined simply, as follows:

val aList = List(1,2,3,4) 

The syntax shown declares and instantiates the linear sequence with the elements provided. The runtime representation of the list constructed will look like this:

1 :: 2 :: 3 :: 4 :: Nil 

Here, Nil represents the end of the list. It's normal to represent an empty list as Nil. The preceding representation is also a way to construct a list, and this is possible because of the "::" operator. This is called the cons operator, and it is used to construct a list. It's a right-associative operator...