Exception handling and object-oriented programming: towards a synthesis

The paper presents a discussion and a specification of an exception handling system dedicated to object-oriented programming. We show how a full object-oriented representation of exceptions and of protocols to handle them, using meta-classes, makes the system powerful as well as extendible and solves many classical exception handling issues. We explain the interest for object-oriented programming of handlers attached to classes and to expressions. We propose an original algorithm for propagating exceptions along the invocation chain which takes into account, at each stack level, both kind of handlers. Any class can control which exceptions will be propagated out of its methods; any method can provide context-dependant answers to exceptional events. The whole specification and some keys of our Smalltalk implementation are presented in the paper.