Delegation vs Inheritance for Typestate Analysis

For several decades, inheritance and delegation have been widely adopted for code reuse in object-oriented languages. Though extensive research has explored the expressiveness of these techniques, little is known about how the choice be-tween them affects formal reasoning. In this paper, we ex-plore this question by describing two core languages that are identical except for the use of inheritance and delega-tion, respectively. We add support for formal reasoning about typestate to both languages, and evaluate the complexity of the formal semantics and compare the example specifica-tions. Our study suggests that our variant of delegation can substantially simplify typestate reasoning, while inheritance makes code more succinct in the case where open recursion is used. 1