A Parameterized Type System for Simple Loose Ownership Domains

Ownership Domains generalize ownership types. They support programming patterns such as iterators that are not possible with ordinary ownership types. However, they are still too restrictive for cases in which an object X wants to access the public domains of an arbitrary number of other objects, which often happens in observer scenarios. To overcome this restriction, we develop so-called loose domains which abstract over several precise domains. Similar to the relation between supertypes and subtypes, we get a relation between loose and precise domains. In addition, we simplify ownership domains by reducing the number of domains per object to two and hard-wiring the access permissions between domains. We formalize the resulting type system for an OO core language and prove type soundness and a fundamental accessibility property.