A value can belong to many types

B H Venter
Department of Computer Science, University of Port Elizabeth
P.O. Box 1600, Port Elizabeth, 6000 South Africa
e-mail: csabhv@upe.ac.za (now hermanv@microsoft.com)

Abstract

Most statically typed Algol-style languages were designed to conform with the view that a value belongs to one and only one type. The adoption of this view bought compiler simplicity at the expense of language expressivity. This trade off has been partially offset by the introduction of subtypes. The adoption of the view that types may intersect in arbitrary ways, on the other hand, requires complicated compilers or costly run-time type checks. However, language expressivity is enhanced, language semantics are simplified and object-oriented and database concepts can be integrated smoothly with the Algol style.

Keywords: Data abstraction, object-oriented programming, polymorphism, type checking

Computing Reviews Categories: D.3.3

• Introduction
• Types as sets
• Related work
• Type equivalence
• Assignment compatibility
• Problems with records
• Types as values
• Dynamic Types
• Object Classes
• Beyond Classes
• Summary
• Conclusion
• References