Object-oriented programming with protected types in Ada 95

Integrating concurrent and object-oriented language facilities is currently an active research area. There are a few experimental languages which attempt to combine various models of concurrency within an OOP framework. Most of these suffer from the so called inheritance anomaly where a concurrent object´s synchronisation code needs to be modified if the object is extended. Ada 95 has avoided some of these problems by integrating protected types into the model of type extensibility. However this has been at the expense of some loss of generality. This paper considers three paradigms of combining protected types with the type extension. The strengths and weaknesses of each approach is discussed. We conclude that none of the approaches are entirely satisfactory and they either suffer from the inheritance anomaly or preclude further extensions