Command Revisited

This pattern revisits the Command [GoF] and Command Processor [POSA1] patterns. The reasons for this revisiting is that we think that the Command and Command Processor patterns do not really capture the essence of what the Command pattern is. We think that Command is basically a way to emulate the concept of closures in object-oriented languages that don't natively have this feature. The Command Revisited pattern packages a piece of application functionality as well as its parameterization in an object in order to make it usable in another context, such as later in time or in a different thread. Example Suppose you are building a complex communication software. The individual sub-sequences of the protocol are similar, but not quite identical. The sub-sequences contain logic that operates on some form of state, also called context. For the various sub-sequences, adapted context information is necessary. Because of maintainability and to keep the footprint small—the communication software is to be used in an embedded device—you want to reuse repeating sub-sequences. For example in the figure above you can detect process step " B " be involved in protocol I as well as in protocol II. The state on which the sub-sequence depends is similar in both cases. The isolation of reusable sub-sequences is the result of an in-depth analysis of the communication protocol. How can