Scala - Is there any way to convert pattern matching into if / else?

Question

I unsuccessfully tried to implement the flatten function in Scala, but did find this implementation here:

def flatten(xs: List[Any]): List[Any] = xs match {
case Nil => Nil
case (head: List[_]) :: tail => flatten(head) ++ flatten(tail)
case head :: tail => head :: flatten(tail)
}

Now, is there any way to write this in terms of if/else? I'm trying to wrap my head around pattern matching, and it would help to see an if/else implementation of this pattern matching. I understand that (head: List[_]) :: tail means something like "if xs is a list with a head that's also a list and tail", but can't find a way to rewrite this in terms of if/else. Is pattern matching the same as if/else, or is it a completely different construct than it? Can all if/else statements be made into pattern matching, and vice versa? Thank you.

jdevelop jdevelop · Accepted Answer · 2013-12-08T05:02:34

Should be something like this:

 if (xs.isInstanceOf[List]) {
   val lst = xs.asInstanceOf[List]
   if (lst == Nil) {
     Nil
   } else if (lst.head.isInstanceOf[List]) {
      flatten(lst.head.asInstanceOf[List]) ++ flatten(lst.tail)
   } else {
      lst.head :: flatten(lst.tail)
   }
 }

Scala - Is there any way to convert pattern matching into if / else?

1 Answers