Dynamically extensible objects in a class-based language

Object oriented programming techniques support the construction of reusable and extensible code. However, class-based languages have poor support for implementing type-orthogonal behavior and extending non-leaf classes, which results in implementations with poor performance or limited functionality. We present dynamic slots, a mechanism for extending objects at runtime. We show how this mechanism can be used to build efficient implementations of type-orthogonal abstractions. Dynamic slots are statically typed and have been integrated into the BETA programming language. Measurements of a persistent store show that they significantly improve performance.