Multiple Inheritance via Intersection Types

Combining intersection types with higher-order subtyping yields a typed model of object-oriented programming with multiple inheritance. Objects, message passing, subtyping, and inheritance appear as programming idioms in a typed-calculus, a modelling technique that facilitates experimentation and helps in distinguishing between essential aspects of the object-oriented style |encapsulation and sub-type polymorphism, which are directly reeected in the low-level type system | and useful but inessential programming idioms such as inheritance. The target calculus, a natural generalization of system F ! with intersection types, is of independent interest. We establish basic structural properties and give a proof of type soundness using a simple semantics based on partial equivalence relations.