Generalized Message Passing in a Virtual Reality Application

The message passing semantics of an object-oriented programming language is one of the factors that determines how powerful the language is. Whether it is referred to as a \method invocation, " a \dispatching call, " an \event, " a \signal, " or something else, each object-oriented programming language supports some operation that is similar in e ect to \message passing." What di ers from language to language is the semantics of that message passing. These semantics largely determine the degree to which an object-oriented language supports polymorphism, overloading, type checking, and abstraction. Although it is theoretically possible to implement anygiven application in any computationally complete language, the exibility of the language that is used will, in practice, have a great in uence over the shape of the nal product. Those features that are extremely di cult to implement in the language being used are less likely to be implemented. If the project is one where the choice of programming language is not as important as the quality of the nal product, such as in a research environment, then it is wise to investigate the alternatives. Virtual reality is one research application that can easily be hampered by the limitations inherent in a programming language. We de ne the concepts of recipient resolution and action resolution, discuss their application to virtual reality, and suggest an approach for extending Objective C to support them.