Partial Dispatch: Optimizing Dynamically-Dispatched Multimethod Calls with Compile-Time Types and Runtime Feedback

Dylan is an object-oriented language with a combination of features that present both difficulties and opportunities for efficient compilation. The language is thoroughly objectoriented and supports multimethod dispatch as well as dynamic typing. The semantics of the language are consistently defined in terms of a program runtime model. However, the design goals included providing significant opportunities for compile-time optimizations that are consistent with this runtime model. Additionally, the ability to dynamically add classes and methods is balanced by the ability to seal branches of the class and method hierarchy, thereby declaring them invariant. Optimization proceeds through a pay-as-you-go strategy. Programmers are not required to choose between the extremes of full static dispatch with strict typing and full runtime dispatch with dynamic typing. Instead, type information and constraints can be added incrementally, with resulting incremental improvements in performance, ultimately resulting in performance equivalent to static languages when full type information is available at compile-time. Additional requirements on Functional Developer include the need to support interactive software development and the production of components using separate compilation. The latter requirement a real world constraint for commercial development rules out the possibility of using many whole program analysis techniques. Instead, Functional Developer makes aggressive use of partial type information available at compile-time, and uses novel techniques to combine this with runtime information to produce highly efficient code.