Variables and Parameters as References and Containers

Most designers of object-based languages adopt a reference model of variables without explicit justiication, despite its wide ranging consequences. This paper argues that the traditional container model of variables is more eecient than the reference model, nearly as exible, and more appropriate to parallel and distributed systems. The topics addressed are object lifetime and its implications for storage management, dynamic typing and its implications for object representation, aliasing and its implications for interference between operations, parameter passing and its implications for communication, and sharing and its implications for contention. We present our experience with the container model in a prototype parallel language. Neither model is always better than the other, and the choice of model should not be left to default.