4.5 Related Work

We categorize related work on polymorphic type systems for object-oriented languages into several groups: languages based on F-bounded polymorphism and explicit subtyping, languages based on SelfType or matching, languages based on signature constraints and implicit structural subtyping, languages based on instantiation-time checking, languages based on covariant redefinition, and languages offering local type inference. Cecil includes the core expressiveness of both F-bounded polymorphism (and its restrictions SelfType and matching) and signature constraints, provided uniformly over a wide range of declarations. Except where noted below, other languages based on these ideas support strict subsets of the expressiveness of Cecil, although sometimes with more compact syntax. Also, the other languages do not support multi-methods, complete separation of inheritance from subtyping, and least-upper-bound and greatest-lower-bound type expressions, except where noted below. In most other systems, classes corresponds to Cecil's abstract or template objects with parallel subtype and inheritance hierarchies.