What's the difference between :: and ::: in Scala

Question

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

then

list1::list2 returns:

List[Any] = List(List(1, 2), 3, 4)

list1:::list2 returns:

Lis         


        

Answer 1

:: prepends a single item whereas ::: prepends a complete list. So, if you put a List in front of :: it is taken as one item, which results in a nested structure.