C# 3.0 Design Patterns

Pattern Comparison

I grouped the Composite and Flyweight patterns in this chapter because they both deal with structures of multiple objects. The Composite pattern is concerned with reacting to commands for accessing and altering a data structure in a uniform way, whereas the Flyweight pattern is a clever way of saving space when there are multiple identical objects. They both have the property that the types making up the pattern can be packaged into a namespace and then used by a client.

In our examples, the CompositePattern namespace was programmed generically, giving any client the built-in flexibility of instantiating the pattern to suit its needs. The constraints that I mentioned at the time were that a type used for instantiating Component needed to have Equals and ToString methods defined. The Equals method is essential for the correct working of the Find method, but the ToString requirement can be dispensed with if different output is arranged. The FlyweightPattern namespace, on the other hand, contains the IFlyweight and Flyweight types, which are very specific to the photo application used for illustration. (It also contains the FlyweightFactory class, which is not dependent on any class from the client.)

Flyweight is a server pattern in the sense that it can be useful to many other patterns to keep data compact. Examples we will encounter later are the Interpreter, State, and Strategy patterns. The Composite pattern is also useful in combination with other patterns that ...