Semantics-Driven Language Design: Statically Type-safe Virtual Types in Object-oriented Languages

The virtual class 15] construct was rst introduced in the language Beta to provide added expressiveness when used with inheritance. Unfortunately, the virtual class construct in Beta is not statically type-safe. In this paper we show how a generalization of the semantics of object-oriented languages with a MyType construct leads to a variant of virtual classes which needs no run-time checks. This results in an object-oriented language in which both parametric types and virtual classes (or types) are well-integrated, and which is statically type-safe.