ObjVlisp

Abstract: This paper discusses the introduction of explicit metaclasses a 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 a la Smalltalk and explicit metaclasses a 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.

Abstract: This paper shows how an attempt at a uniform and reflective definition resulted in an open-ended system supporting ObjVlisp, which we use to simulate object-oriented language extensions. We propose...

Abstract: One of the main goals of object-oriented languages is to unify their universe: "every entity of the language is an object. The class concept, however, usually does not follow this wish: a class being not a real object, i.e., created from a class. The metaclass concept introduced in Smalltalk- 80, attempts to give classes a first class citizenship but complicates the instantiation scheme without solving its fundamental limitations: the only partial specification of the class at the metaclass level, and the fixed number of meta-levels. Some more recent approaches, as in Loops and then CommonLoops, tend towards a better unification, but reveal the same limitations. We propose to go one step further and present an ultimate new model for an optimal simplification of the class/object concept, while keeping the class abstraction. In this model, implemented by ObjVlisp, every object is an instance of a class, and a class is a true object fully specified at the meta-level. A metaclass is a true class inheriting from another one. Because ObjVlisp is built on a reflective architecture, the user has uniform access and control to all the levels of the language: class level, metaclass level... He can add new levels and the metaclass links can be created indefinitely. Finally, we suggest to clarify the Smalltalk terminology with a new definition for class variables: the instance variables of a class - treated as an object - become the class variables of this class, explicitly expressed at the metaclass level.

Abstract: This paper discusses the introduction of explicit metaclasses la ObjVlisp into the Smalltalk-80 language. The rigidity of Smalltalk metaclass architecture motivated this work. We decided to impleme...