on 30-Oct-2014 (Thu)

all value classes are subtypes of scala.AnyVal, but they do not subclass each other. Instead there are implicit conversions between different value class types. For example, an instance of class scala.Int is automatically widened (by an implicit conversion) to an instance of class scala.Long when required.

The methods min, max, until, to, and abs are all defined in a class scala.runtime.RichInt, and there is an implicit conversion from class Int to RichInt. The conversion is applied whenever a method is invoked on an Int that is undefined in Int but defined in RichInt.

Nothing is a subtype of every other type

there exist no values of type Nothing

def error(message: String): Nothing =
  throw new RuntimeException(message)

The return type of error is Nothing, which tells users that the method will not return normally (it throws an exception instead).

Because Nothing is a subtype of every other type, you can use methods "returning" Nothing wherever any expression of any type is expected.