On the (un)reality of Virtual Types Didier R Emy and J Er^ Ome Vouillon

We show, mostly through detailed examples, that programming patterns known to involve the notion of virtual types can be implemented directly and concisely using parametric poly-morphism. A signiicant improvement we make over previous approaches is to allow related classes to be deened independently. This solution is more exible, more general, and we believe, simpler than other type-safe solutions previously proposed. This approach can be applied to several languages with parametric polymorphism that can already type binary methods and have structural object types. We conclude that parametric polymorphism is always better than virtual types. Moreover, it avoids the introduction of a new non-atomic primitive construct.