ACTS: A Type System for Object-Oriented Programming Based on Abstract and Concrete Classes

The inheritance mechanism facilitates incremental modification and is the basis for the many advantages and popularity of the object oriented paradigm. The overloading of inheritance to describe different relationship requires a semantic model to facilitate “safe” redefinition between classes. Current approaches use type systems to ensure “safe” redefinitions, and are not capable of handling all the different uses of inheritance naturally. This paper develops a uniform type system built on a hierarchy which distinguishes between abstract and concrete classes. We show how such a structure on the hierarchy can be exploited to describe all common uses of inheritance in a natural way. Finally, we develop the formalism to define abstract and concrete classes and their relationships; and the type system along with the static type checker and the semantic model to interpret type safety.