Family Polymorphism

This paper takes polymorphism to the multi-object level. Traditional inheritance, polymorphism, and late binding interact nicely to provide both flexibility and safety — when a method is invoked on an object via a polymorphic reference, late binding ensures that we get the appropriate implementation of that method for the actual object. We are granted the flexibility of using different kinds of objects and different method implementations, and we are guaranteed the safety of the combination. Nested classes, polymorphism, and late binding of nested classes interact similarly to provide both safety and flexibility at the level of multi-object systems. We are granted the flexibility of using different families of kinds of objects, and we are guaranteed the safety of the combination. This paper highlights the inability of traditional polymorphism to handle multiple objects, and presents family polymorphism as a way to overcome this problem. Family polymorphism has been implemented in the programming language gbeta, a generalized version of Beta, and the source code of this implementation is available under GPL.1