5_nullChecks.swift

/**
 * A reference must be explicitly marked as nullable to be able hold a null.
 * See http://kotlinlang.org/docs/reference/null-safety.html#null-safety
 */

// Return nil if str does not hold a number
func parseInt(str: String) -> Int32? {
  do {
    return try Integer.parseInt(str)
  } catch {
    print("One of the arguments isn't Int32")
  }
  return nil
}

func main(args: [String]) {
  if args.size < 2 {
    print("No number supplied");
  } else {
    let x = parseInt(args[0])
    let y = parseInt(args[1])

    // We cannot say 'x * y' now because they may hold nulls
    if x != nil && y != nil {
      print(x! * y!) // Now we can
    } else {
      print("One of the arguments is nil")
    }
  }
}

main([])