Fast Algorithms for Compressed Multi-Method Dispatch Tables Generation

The eeciency of dynamic dispatch is a major impediment to the adoption of multi-methods in object-oriented languages. In this paper, we propose a simple multi-method dispatch scheme based on compressed dispatch tables. This scheme is applicable to any object-oriented language using a method precedence order that satisses a speciic monotonous property (e.g., as Cecil and Dylan), and guarantees that dynamic dispatch is performed in constant time, a major requirement for some languages and applications. We provide eecient algorithms to build the dispatch tables, provide their worst-case complexity, and demonstrate the eeectiveness of our scheme by real measurements performed on two large object-oriented applications. Finally, we provide a detailed comparison of our technique with other existing techniques. 1. INTRODUCTION In traditional object-oriented systems such as Smalltalk Goldberg and Robson 1983] and C++ Ellis and Stroustrup 1992], functions have a specially designated target argument, sometimes called receiver, whose type, determined either at run-time or at compile-time, serves to select the method to execute in response to a function invocation. Multiple dispatching, rst introduced in CommonLoops Bo-brow et al. 1986] and CLOS Bobrow et al. 1988], generalizes this form of dynamic binding by selecting a method depending on the run-time type of a subset of the arguments of a function invocation. Methods in this generalized scheme are called