Dynamic contracts for adaptive specification

We present a novel approach to the reuse of classes and specifications. To match the flexibility provided at implementation level by notions like inheritance, we propose Dynamic Contracts to extend the expressiveness of specification assertions. We also show that a stronger notion of behavioural subtyping is necessary in this setting and for this purpose provide Reinforced Behavioural Subtyping. We show that the resulting formalism can handle the Fragile Base Class problem and can specify the behaviour associated with the Observer Design Pattern.