Design Patterns Explained

2O8 Part IV • Putting It All Together: Thinking in Patterns
Start with the
canonical form
.. . and map classes
into it
Figure 12-6 Using inheritance to handle the two model types.
Figure 12-7 Using the Bridge pattern to handle the two model types.
Note that I do not really have a Bridge pattern in Figure 12-7
because Model is not varying except for the implementation. In the
Feature, I have different types of Features that have different
types of implementations— a Bridge pattern does exist here.
I start implementing the Bridge pattern by using Feature as the
abstraction and using V1 and V2 as the basis for the implementations.
To translate the problem into the Bridge pattern, I start with
the standard example of the Bridge pattern and then substitute
classes into it. Figure 12-8 shows the standardized, simplified form
(sometimes called the canonical form).
In the problem, Feature maps to Abstraction. There are five dif -
ferent kinds of features: slot, hole, cutout, irregular, and special.
The implementations are the V1 and V2 systems; I choose to name
the classes responsible for these implementations viimp and
V2lmp, respectively.