scala main returns unit. How to set program's return value

Question

The method prototype for main is:

def main(args: Array[String]): Unit

Typically, an application needs to specify a return code when it exits. How is that typically done in scala if main returns Unit? Should I call System.exit(n)?

Also, the docs warn that I should not use main at all, though this seems at odds with the getting started guide).

What's the best practice here?

Answer 1

Yes, you exit with a code different than zero by calling either java.lang.System.exit(n) or better sys.exit(n) (which is Scala's equivalent).

If you mix in App in your main application object, you do not define method main but can just write its contents in the object's body directly.

E.g.

object Test extends App {
  val a0 = args.headOption.getOrElse {
    Console.err.println("Need an argument")
    sys.exit(1)
  }
  println("Yo " + a0)
  // implicit: sys.exit(0)
}