Programming with explicit metaclasses in Smalltalk-80

This paper discusses the introduction of explicit metaclasses á la ObjVlisp into the Smalltalk-80 language. The rigidity of Smalltalk metaclass architecture motivated this work. 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 combining implicit metaclasses á la Smalltalk and explicit metaclasses á 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.