Arguments and Results

If an object-oriented program is a collection of communicating objects, then the objects' protocols define the languages the program speaks. Unfortunately, protocols are difficult to design in isolation, so many programs' protocols are not as well designed as they could be. This paper presents six patterns which describe how objects' protocols can be designed or redesigned, by considering the arguments the protocols accept and the results the protocols return. By using these patterns, programs and designs can be made simpler, more general, and easier to change.