C# 3.0 Design Patterns

Pattern Comparison

The careful reader might have noticed that the three patterns described in this chapter seem to offer much the same service. At a high level, they are all helping to extend classes in novel ways, and they all provide alternatives to inheritance. A summary of when each pattern might be used was provided at the end of each section. Because this is also a programming book, we'll now summarize the object mechanisms the patterns use (see Table 2-2) and draw conclusions about their comparative operation. This summary is based on the UML diagrams and theory code for each of the patterns.

In each pattern, we can identify four roles, which can fall under the headings original, new, interface, and client. The actual names given to these meta-roles are shown in the first three rows of the table. Note that the Bridge pattern can work in two ways. In our examples, we used the "Bridge-up" option. We assumed that we had one implementation already and wanted to share its interface with other implementations yet to be built. To do so, we needed to create an Abstraction that was closely connected to the Bridge interface. An equally valid application for the Bridge pattern would be to have an original abstraction in mind and to build it hand-in-hand with the implementations (the "Bridge-down" approach).

Table 2-2. Comparison of Decorator, Proxy, and Bridge patterns

Â	Decorator	Proxy	Bridge-down	Bridge-up
Original	Component	Subject	Abstraction	Implementation
Interface	IComponent	ISubject	Bridge ...