Strong typing of object-oriented languages revisited

  • Authors:

  • Ole Lehrmann Madsen;Boris Magnusson;Birger Mølier-Pedersen

  • Affiliations:

  • Computer Science Department, Aarhus University, Ny Munkegade, DK-8000 Aarhus C, Denmark;Department of Computer Science, University of Lund, PoBox 118, S-221 00 Lund, Sweden;Norwegian Computing Center, P.O. Box 114, Bliudern, N-0314 Oslo 3, Norway

  • Venue:
  • OOPSLA/ECOOP '90 Proceedings of the European conference on object-oriented programming on Object-oriented programming systems, languages, and applications
  • Year:
  • 1990

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Abstract

This paper is concerned with the relation between subtyping and subclassing and their influence on programming language design. Traditionally subclassing as introduced by Simula has also been used for defining a hierarchical type system. The type system of a language can be characterized as strong or weak and the type checking mechanism as static or dynamic. Parameterized classes in combination with a hierarchical type-system is an example of a language construct that is known to create complicated type checking situations. In this paper these situations are analyzed and several different solutions are found. It is argued that an approach with a combination of static and dynamic type checking gives a reasonable balance also here. It is also concluded that this approach makes it possible to base the type system on the class/subclass mechanism.