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Source Code

The ICloneableExample project is located under the Chapter 9 subdirectory.

Another limitation of traditional abstract base classes is that each and every derived type must

contend with the set of abstract members and provide an implementation. To see this problem,

recall the shapes hierarchy we defined in Chapter 6. Assume we defined a new abstract method in

the Shape base class named GetNumberOfPoints(), which allows derived types to return the number

of points required to render the shape:

abstract class Shape

{

...

// Every derived class must now support this method!

public abstract byte GetNumberOfPoints();

}

Clearly, the only type that has any points in the first place is Hexagon. However, with this

update,

every derived type (Circle, Hexagon, and ThreeDCircle) must now provide a concrete imple-

mentation of this function even if it makes no sense to do so.

Again, the interface type provides a solution. If we were to define an interface that represents

the behavior of “having points,” we could simply plug it into the Hexagon type, leaving Circle and

ThreeDCircle untouched.