What are the underlying types of Scala
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At the bottom of the type hierarchy are two classes scala.Null and Scala.Nothing. They are special types that deal with the "boundary case" of some Scala object-oriented type systems in a unified way.
The class Null is a reference to the null type; it is a subclass of each reference class (that is, every class that inherits from AnyRef). Null is not compatible with value types. You cannot, for example, assign a null value to an integer variable:
Scala > val I: Int = null
< console>: 4errorRanger typemismatch; found:Null (null) required:Int
The type Nothing is on the * side of the class level of Scala; it is a subtype of any other type. However, there is no value of this type at all. What's the point of having a type with no value? One of the uses of Nothing is that it marks an abnormal termination. For example, the Predef object in Scala's standard library has an error method, which is defined as follows:
Def error (message:String): Nothing = throw new RuntimeException (message)
The return type of error is Nothing, which tells the user that the method does not return normally (instead, an exception is thrown). Because Nothing is a subclass of any other type, you can use methods like error very flexibly. For example:
Def divide (x:Int, y:Int): Int = if (y! = 0) x / y else error ("can't divide by zero")
The "then" state branch, x / y, is of type Int, while the "otherwise" (else) branch calls error with type Nothing. Because Nothing is a subtype of Int, the type of the entire state statement is Int, as needed.
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