Meta-programming Composers In Second-Generation Component Systems

Future component systems will require that components can be composed exibly. In contrast to current systems which only support a xed set of composition mechanisms, the component system should provide a composition language in which users can deene their own speciic composers. It is argued for an object-oriented setting that this will be possible by meta-programming the class-graph. Composers will be based on two important elements. First, they will express coupling by graph-based operators which transform parts of the class-graph (coupling design patterns). Second, during these transformations, elementary meta-operators will be used to transform data and code, rearranging slots and methods of parameter-components. Thus during their reuse, components are queried by introspection and transformed by meta-programming. Composers that use meta-programming generalize connectors in architectural languages. Hence they encapsulate context-dependent aspects of a system, and make components independent of their embedding context. Since meta-programming composers may change behavior of components transparently, meta-programming composers will lead to a nice form of grey-box reuse, which supports embedding of components (and classes) into application contexts in a new and exible way.