A reflective implementation of Java multi-methods

Abstract

Abstract-In Java, method implementations are chosen at runtime by late-binding with respect to the runtime class of just the receiver argument. However, in order to simplify many programming designs, late-binding with respect to the dynamic type of all arguments is sometimes desirable. This behavior, usually provided by multi-methods, is known as multi-polymorphism. This paper presents a new multi-method implementation based on the standard Java reflection mechanism. Provided as a package, it does not require any language extension nor any virtual machine modification. The design issues of this reflective implementation are presented together with a new and simple multi-method dispatch algorithm that efficiently supports class loading at runtime. This implementation provides a practicable and fully portable multi-method solution.

Reflection-based implementation of Java extensions: the double-dispatch use-case.

“…For instance, they could wish to have a double-dispatch mechanism to ease implementations dealing with tree-like structures or binary methods [4,17]. This feature, which is a special case of multi-methods [11,21,8,3,22,23,10,12,1,27,2,14], allows a method implementation to be chosen with respect to the dynamic type (late-binding) of both the receiver and a single argument. It can be achieved programmatically through the visitor design pattern [19,15].…”