. Support for modular evolution of objects is required in many application areas. However, existing mechanisms for incremental behavior composition either do not support evolving objects at all, or do not satisfactorily solve the encapsulation and name collision problems associated with them. In this paper, a new approach to behavior composition in a class-based environment is presented. It is based on the encapsulated object model of class-based inheritance, but introduces an additional abstraction layer between objects and classes. By being responsible for the compositional aspects of the behavior of objects, this layer provides support for the evolution of behavior while at the same time solving the name conflicts that may occur. A formal description of the approach is provided and its feasibility is demonstrated by implementing it as a metalevel extension of Smalltalk-80. 1 Introduction In several object-oriented application areas, support for dynamic and incremental evolution of ...

The definition of a class library is an iterative process involving both the designer who provides basic functionality, and the users who subsequently specialize it. In order to ensure the coherence of possible modifications, suitable means for coordinating the activity of both are required. In this paper, we propose a metaclass based approach for bridging the gap between library designers and specializers, by enabling the designer to express specialization constraints which are automatically imposed on all possible modifications. The approach adopted for the design of the meta-level provides for modularity and extensibility. It is based on a dispersed meta-representation of how classes behave and an automatic metaclass construction by deriving procedural code from a set of metadescriptions chosen according to the constraints to be satisfied. 1 Introduction In contrast to conventional procedural libraries, object-oriented class libraries allow users to extend the offered functionali...