Tribal ownership.

Tribal Ownership unifies class nesting and object ownership. Tribal Ownership is based on Tribe, a language with nested classes and object families. In Tribal Ownership, a program's runtime object ownership structure is characterised by the lexical nesting structure of its classes. We build on a variant of Tribe to present a descriptive ownership system, using object nesting to describe heap partitions, but without imposing any restrictions on programming disciplines. We then demonstrate how a range of different prescriptive ownership policies can be supported on top of the descriptive Tribal Ownership mechanism; including a novel owners-as-local-dominators policy. We formalise our type system and prove soundness and several ownership invariants. The resulting system requires strikingly few annotations, and uses well-understood encapsulation techniques to create ownership systems that should be intuitive for programmers.