Message Passing - Mathematical Models

Mathematical Models

The prominent mathematical models of message passing are the Actor model and Pi calculus.

In the terminology of some object-oriented programming languages, a message is the single means to pass control to an object. If the object "responds" to the message, it has a method for that message. In pure object-oriented programming, message passing is performed exclusively through a dynamic dispatch strategy.

Objects can send messages to other objects from within their method bodies. Message passing enables extreme late binding in systems. Sending the same message to an object twice will usually result in the object applying the method twice. Two messages are considered to be the same message type, if the name and the arguments of the message are identical. Some languages support the forwarding or delegation of method invocations from one object to another if the former has no method to handle the message, but "knows" another object that may have one. See also Inversion of Control.

Alan Kay has argued that message passing is more important than objects in OOP, and that objects themselves are often over-emphasized. The live distributed objects programming model builds upon this observation; it uses the concept of a distributed data flow to characterize the behavior of a complex distributed system in terms of message patterns, using high-level, functional-style specifications.