Correctness of intrusive data structures using mixins

A dynamic mixin is a code fragment that is meant to be dynamically bound to an object. Dynamic mixins support more flexible code composition than class inheritance and can be used to implement roles that objects acquire dynamically. We propose a theory, based on data refinement, for reasoning about the correctness of programs with mixins. The theory is suited for applications of mixins to intrusive data structures, where the data structure is spread over existing objects. We illustrate this with two examples, one-to-one association and union-find data structures.