Matching ThisType with Subtyping

By Chieri Saito and Atsushi Igarashi. In Proceedings of the 24th Annual ACM Symposium on Applied Computing (SAC2009), pages 1851-1858, Honolulu, HI, March 2009.


The notion of ThisType has been proposed to promote type-safe reuse of binary methods and recently extended to mutually recursive definitions. It is well-known, however, that ThisType does not match with subtyping well. In the current type systems, type safety is guaranteed by the sacrifice of subtyping, hence dynamic dispatch. In this paper, we propose two mechanisms, namely, nonheritable methods and local exactization to remedy the mismatch between ThisType and subtyping. We rigorously prove their safety by modeling them in a small calculus.