Modularity meets inheritance

Journal ArticleWe "unbundle" several roles of classes in existing languages, by providing a suite of operators independently controlling such effects as combination, modification, encapsulation, name resolution, and sharing, all on the single notion of module. All module operators are forms of inheritance. Thus, inheritance not only is not in conflict with modularity in our system, but is its foundation. This allows a previously unobtainable spectrum of features to be combined in a cohesive manner, including multiple inheritance, mixins, encapsulation and strong typing. We demonstrate our approach in a language (called Jigsaw, as in t h e tool, not the puzzle!). Our language is modular in two senses: it manipulates modules, and it is highly modular in its own conception, permitting various module combinators to be included, omitted, or newly constructed in various realizations. We discuss two pragmatic avenues for the exploitation of this approach: 1. Adding modules to languages without modularity constructs. 2. Embedding selected new modularity capabilities within existing object-oriented languages (which we are undertaking as a "proof of concept" in the case of Modula-3 [5]).