9.10 Looking Ahead

Mechanistic design is concerned with specifying the details of inter-object collaboration. Parameterized patterns for small groups of objects acting together within collaborations are referred to as mechanisms. Mechanistic design takes the collaborative groups of objects identified in analysis and adds design-level objects to facilitate and optimize their implementation. For example, containers and iterators are added to manage associations consisting of multiple objects. Smart Pointer objects glue associations together in such a way as to eliminate memory leaks and inappropriate pointer dereferencing. Policy objects abstract away strategies and algorithms from their context so that they can be easily modified or replaced, even while the system executes.

Many of the objects added during mechanistic design reappear in many designs because they solve problems common to many systems. These collaborations are reified into mechanistic design patterns. These patterns are templates of object interaction consisting of a problem, context, and a structural solution. The reification of the patterns allows them to be cataloged and studied systematically so they can be used again in future projects. This chapter presented a number of patterns useful in mechanistic design. You are invited to explore the references at the end of the chapter for more patterns.

Chapter 10 discusses the detailed design of object-oriented systems in a real-time context. Detailed design is concerned with the implementation of data structures and algorithms within the scope of a single class. Space and time complexity tradeoffs are made during detailed design in order to achieve the performance requirements specified for your system.