Scala Reactive Programming

Scala List Cons operator

In Scala, List has an operator ::, which is known as the Cons operator. It is useful to add new elements at the beginning of the List. Here, Cons is short for construct the new List object.

Let us explore the Cons operator with some simple examples (here :: is a double colon):

scala> var numbersList = List (1,2,3) 
numbersList: List[Int] = List(1, 2, 3) 
 
scala> numbersList = numbersList :: 4 
<console>:11: error: value :: is not a member of Int 
       numbersList = numbersList :: 4 
                                 ^ 

We cannot use the Cons operator to add a new element at the end of the List. It accepts it only to add it at the beginning of the List:

scala> numbersList = 4 :: numbersList numbersList: List[Int] = List(4, 1, 2, 3) scala> numbersList = 6 :: 5 ...