Dynamic Inheritance and Static

In the area of object-orientation there is a long-standing schism between the rigid but safe statically typed languages, and the expressive and exible but less safe \typeless" languages. Many eeorts have aimed at combining the best of both. This paper presents a language mechanism which enhances the exibility and expressivity of static languages while preserving the safety properties. It is an inheritance mechanism, with standard single inheritance as a special case. It allows both compile-time and run-time construction of new classes. Moreover , it supports specialization of existing objects at run-time. This helps avoiding the combinatorial explosion in the number of classes associated with multiple inheritance, and it supports a better separation of concerns in large systems. Pre-methoding|inheritance applied to behavioral descriptors|has been used for the construction of control structures for many years, in Beta. With dynamic inheritance, pre-methoding becomes more expressive, supporting control structures as rst class values which may be constructed and combined dynamically. Even though the concept of pre-methoding is missing from most other languages, the basic idea could be applied to any statically typed object-oriented language.