Refined Effects for Unanticipated Object Re-classification: $\mathcal{F}ickle_{\rm 3}$

Abstract

In previous work on the language $\mathcal{F}ickle$ and its extension $\mathcal{F}ickle_{II}$ Dezani and us introduced language features for object re-classification for imperative, typed, class-based, object-oriented languages.

In this paper we present the language $\mathcal{F}ickle_{3}$, which on one side refines $\mathcal{F}ickle_{II}$ with more expressive effect annotations, and on the other eliminates the need to declare explicitly which are the classes of the objects that may be re-classified. Therefore, $\mathcal{F}ickle_{3}$ allows to correctly type meaningful programs which $\mathcal{F}ickle_{II}$ rejects. Moreover, re-classification may be decided by the client of a class, allowing unanticipated object re-classification. As for $\mathcal{F}ickle_{II}$, also the type and effect system for $\mathcal{F}ickle_{3}$ guarantees that, even though objects may be re-classified across classes with different members, they will never attempt to access non existing members.

The type and effect system of $\mathcal{F}ickle_{3}$ has some significant differences from the one of $\mathcal{F}ickle_{II}$. In particular, besides the fact that intra-class type checking has to track the more refined effects, when a class is combined with other classes some additional inter-class checking is introduced.

Work partially supported by IST-2001-33477 DART, MIUR Cofin ‘01 NAPOLI, and MIUR Cofin’02 McTati projects. The founding bodies are not responsible for any use that might be made of the results presented here.