When working with lists in Scala, you’ll often encounter the ::: and :: operators. These operators are essential for list manipulation, but they serve different purposes. In this blog, we’ll explore these operators, their use cases, and how they impact your Scala code.

::: Operator

The ::: operator is used for list concatenation. It combines two lists to create a new list that contains all the elements from both lists. Here’s how it works:

val list1 = List(1, 2, 3)
val list2 = List(4, 5, 6)

val concatenatedList = list1 ::: list2 // Combines list1 and list2

println(concatenatedList) // Output: List(1, 2, 3, 4, 5, 6)

As you can see, the ::: operator takes two lists and produces a new list that contains elements from both lists.

:: Operator

The :: operator, pronounced as “cons,” is used to prepend an element to an existing list, creating a new list. It’s often used for building lists incrementally. Here’s how it works:

val list = List(2, 3, 4)
val newList = 1 :: list // Prepends 1 to the existing list

println(newList) // Output: List(1, 2, 3, 4)

In this example, we’ve prepended the integer 1 to the list, resulting in a new list.

To summarize:

• ::: is used for list concatenation, combining two lists into one.
• :: is used to prepend an element to an existing list, creating a new list.

Understanding the distinction between these operators is essential for working effectively with lists in Scala.