Programming with ObjVlisp Metaclasses in Smalltalk-80

A b s t r a c t This paper discusses the introduction of explicit metaclasses à la ObjVlisp into the Smalltalk-80 language. The rigidity of Smalltalk metaclass architecture motivated this work. Consequently we decided to implement the ObjVlisp model into the standard Smalltalk-80 system. The resulting combination defines the Classtalk platform. This platform provides a full-size environment to experiment with class-oriented programming by composing implicit metaclasses à la Smalltalk and explicit metaclasses à la ObjVlisp. Obviously, these experiments are not limited to the Smalltalk world and will be useful to understand and practice the metaclass concept advocated by modern object-oriented languages such as ObjVlisp and CLOS.