Subtyping-inheritance conflicts: The mobile mixin case

In sequential class-and mixin-based settings, subtyping is essentially a relation on objects: no subtype relation is defined on classes and mixins, otherwise there would be conflicts with the inheritance mechanism, creating type un-safety. Nevertheless, a width-depth subtyping relation on class and mixin types is useful in the realm of mobile and distributed processes, where object-oriented code may be exchanged among the sites of a net. In our proposal, classes and mixins become “first-class citizens” at communication time, and communication is ruled by a type-safe width-depth subtyping relation.