Unit in scala - Not able to understand

Question

Am bogged down by this syntax:

def foreach(f: Tweet => Unit): Unit = {
    f(elem)
    left.foreach(f)
    right.foreach(f)
  }

where Tweet is a class with three variables. What does it mean for a function to return Unit? I tried different things but am not able to call the function itself in this case.

Please help. Thanks

Answer 1

Unit in scala is identical to void in Java, moreover, Java sees Scala's Unit as void, and vise versa. So in java it could be written like:

void foreach(MethodThatReturnsVoid f) {
    f.apply(elem)
    left.foreach(f)
    right.foreach(f)
}

It is a little bit pseudocode (since java doesn't support first class functions yet) but I hope you've got the idea.