What's the difference between :: and ::: in Scala
ScalaScala Problem Overview
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:
List[Int] = List(1, 2, 3, 4)
I saw the book writes that when use :: it also results List[Int] = List(1, 2, 3, 4). My Scala version is 2.9.
Scala Solutions
Solution 1 - Scala
:: 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.
Solution 2 - Scala
In general:
::- adds an element at the beginning of a list and returns a list with the added element:::- concatenates two lists and returns the concatenated list
For example:
1 :: List(2, 3) will return List(1, 2, 3)
List(1, 2) ::: List(3, 4) will return List(1, 2, 3, 4)
In your specific question, using :: will result in list in a list (nested list) so I believe you prefer to use :::.
> Reference: class List int the official site