Abstract from the Introduction

This volume comprises fifteen chapters, by selected authors, on theoretical aspects of object-oriented programming languages. The focus is on type systems and semantic models, and how advances in these areas can contribute to new language designs. The collection is divided into five parts: Objects and Subtypes, Type Inference, Coherence, Record Calculi, Inheritance. The chapters are organized approximately in order of increasing complexity of the language constructs they consider. Put briefly, the collection begins with variations on Pascal- and Algol-like languages, develops the theory of illustrative record object models, and concludes with research directions for developing a more comprehensive theory of object-oriented programming languages. Part I discusses the similarities and differences between objects and algebraic-style abstract data types, and address general problems associated with subtyping (or subclasses) in the presence of operations that may be applied to objects of more than one type. Parts II--IV, which form the core of the collection, are concerned with what may be called the record model of object-oriented languages. More specifically, these chapters discuss static and dynamic semantics of languages with simple object models that include a type or class hierarchy, but do not explicitly provide what is often called dynamic binding or dynamic method lookup. Part II develops the record model incrementally, beginning with a simple extension of the record operations from the language ML. The denotational semantics of these languages are considered in Part III, with more elaborate record object models and more precise connections with object-oriented methodology developed in Part IV. Extensions and modifications to record object models are considered in Part V. These chapters bring us closer to the full complexity of practical object-oriented languages. However, the complete theoretical underpinnings of the language features discussed in Part V remain a topic for future research.