What does `:_*` (colon underscore star) do in Scala?

Question

I have the following piece of code from this question:

def addChild(n: Node, newChild: Node) = n match {
  case Elem(prefix, label, attribs, scope, child @ _         


        

Answer 1

All the above answer looks great, but just need a sample to explain this . Here it is :

val x : Seq[Seq[Int]] = Seq(Seq(1),Seq(2))

def f(arg: Seq[Any]*) : Int = {
 arg.length
}
f(x) //1 as x is taken as single arg
f(x:_*)  // 2 as x is "unpacked" as a Seq[Any]*

So now we know what :_* do is to tell compiler : please unpack this argument and bind those elements to the vararg parameter in function call rather than take the x as a single argument .

So in a nutshell, the :_* is to remove ambiguity when pass argument to vararg parameter.