Calculi for Object Evolution and Adaptation Sample Clauses

Calculi for Object Evolution and Adaptation. Object-oriented languages are usually classified in two families: the object-based and the class-based. In object- based languages (e.g., Self, Python, JavaScript), the unit of decomposition is the object; these are usually untyped or weakly typed. In class-based languages (e.g. Java and C++) the unit of decomposition is the class; these are usually strongly typed. The flexibility of weak typing, and the flexibility of individual objects, make object-based languages very useful in prototyping, where the software production cycle must be short, and also the code produced tends to be short lived. On the other hand, the robustness offered by strong typing, and the more robust design supported by classes, makes class-based languages better suited in the production environment, where software is meant to be the base for (a possibly long) evolution. We aim to design ways of combining the flexibility and the robustness. So far, the following approaches have been suggested: • For object-based languages, robustness has been sought through the addition of suitable type systems, which prevent run-time errors, in particular message-not-understood, see [BCM+93, FHM94, AC96, BCP99]. • For class-based languages, flexibility has been pursued by weakening the typing requirements in languages, like CLOS, where code is broken down on a per-function basis (see wide classes [Ser99], and predicate classes [Cha93]). • Recent research in class-based languages has suggested extensions of strongly typed languages, like Java, where code is broken down on a per-class basis, and where objects may be re-classified, i.e. change their class at run-time, without any need for dynamic checking [DDDCG01a]. We consider the first two approaches not completely satisfactory: the first risks to produce type systems which are too restrictive; the second produces systems that require dynamic checks, which may throw message-not- understood exceptions. We consider the third approach promissing, but it does not support a smooth transition from prototype pro- gramming to the robustness offered by class based languages. We shall therefore extend the work on object re-classification, and incorporate it into a full programming language. We shall also consider evolution of classes themselves, to model situations where code needs to be patched on the fly, without re-booting the system. In these cases, in order to ensure consistency, one needs to identify which objects might be affected, and which code need ...