A Proposal for Harmonising Types, Inheritance and Polymorphism for Object-oriented Programming

Object-Oriented Programming (OOP) has attracted a large following in recent years. Goals for the paradigm have included bringing computational implementations closer to abstractions (the HCI school, exemplified by Smalltalk []), partitioning spaces of concepts (the AI school, exemplified by CLOS []) and software engineering for reuse and extensibility (the SE school, exemplified by Eiffel []). The present trend is away from type-free or dynamically typed languages and towards strong static typing, with some dynamic binding. Attempts to provide formal typed models of OOP have been frustrated by the great flexibility in languages that permit unrestricted redefinition of class properties. The principal difficulty lies in devising a typed functional algebra that conforms to the operational definition of OOP languages, which are usually described in completely different terms.