Question

I am not sure what the difference is between specifying Unit as the return type of my scala method or leaving out the return type altogether. What is the difference?

Can anyone please advise?

Answer 1

Implicit Unit return type:

def f() {println("ABC")}

Explicit Unit return type:

def g(): Unit = {println("ABC")}

Return type inferred from the last method expression, still Unit because this is the type of println, but confusing:

def h() = println("ABC")

All the methods above are equivalent. I would prefer f() because the lack of = operator after method signature alone is enough for me. Use explicit : Unit when you want to extra document the method. The last form is confusing and actually treated as a warning in intellij-idea.

The = operator is crucial. If it is present it means: “please return whatever the last statement returns” in method body. Obviously you cannot use this syntax for abstract methods. If it is not, Unit is assumed.