A Tour of Hybrid A Language for Programming with Active Objects*

Object-oriented programming is a powerful paradigm for organizing software into reusable components. There have been several attempts to adapt and extend this paradigm to the programming of concurrent and distributed applications. Hybrid is a language whose design attempts to retain multiple inheritance, genericity and strong-typing, and incorporate a notion of active objects. Objects in Hybrid are potentially active entities that communicate with one another through a messagepassing protocol loosely based on remote procedure calls. Non-blocking calls and delay queues are the two basic mechanisms for interleaving and scheduling activities. A prototype implementation of a compiler and run-time system for Hybrid have been completed. We shall review aspects of the language design and attempt to evaluate its shortcomings. We conclude with a list of requirements that we pose as a challenge for the design of future concurrent object-oriented languages. *.In Advances in Object-Oriented Software Engineering, ed. D. Mandrioli and B. Meyer, Prentice-Hall, 1992, pp. 167-182. †.Author’s current address: Institut für Informatik und angewandte Mathematik (IAM), University of Berne , Länggassstrasse 51, CH-3012 Berne, Switzerland. Tel: +41 (31) 631.4618. E-mail: [email protected]. WWW: http://www.iam.unibe.ch/~oscar.