Generic Immutability and Nullity Types for an imperative object-oriented programming language with flexible initialization

We present a type system for parametric object mutability and reference nullity in an imperative object oriented language. We present a simple but powerful system for generic nullity constraints, and build on previous work to provide safe initialization of objects which is not bound to constructors. The system is expressive enough to handle initialization of cyclic immutable data structures, and to enforce their cyclic nature through the type system. We provide the crucial parts of soundness arguments (though the full proof is not yet complete). Our arguments are novel, in that they do not require auxiliary runtime constructs (ghost state) in order to express or demonstrate our desired properties.