Return type in If expression

Question

I am learning scala and can\'t understand why:

def signum(arg: Int) = {
    if(arg > 0 ) 1
    else if(arg < 0) -1
    else 0
}

Has

Answer 1

In the absence of an explicit else, Scala assumes this:

else ()

Where () is the value of Unit. It's the value returned by println or assignment to var, for example.

This can be easily verified:

scala> val x = if (false) 1
x: AnyVal = ()

scala> x.isInstanceOf[Unit]
res3: Boolean = true