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Source Code

The InterfaceNameClash project is located under the Chapter 9 subdirectory.

Designing Interface Hierarchies

Interfaces can be arranged into an interface hierarchy. Like a class hierarchy, when an interface

extends an existing interface, it inherits the abstract members defined by the parent type(s). Of

course, unlike class-based inheritance, derived interfaces never inherit true implementation.

Rather, a derived interface simply extends its own definition with additional abstract members.

Interface hierarchies can be useful when you wish to extend the functionality of an existing

interface without breaking existing code bases. To illustrate, create a new Console Application

named InterfaceHierarchy. Now, let’s redesign the previous set of rendering-centric interfaces

(from the InterfaceNameClash example) such that IDrawable is the root of the family tree:

public interface IDrawable

{

void Draw();

}

Given that IDrawable defines a basic drawing behavior, we could now create a derived interface

that extends this type with the ability to render its output to the printer. Assume this method is

called Print():

public interface IPrintable : IDrawable

{

void Print();

}

And just for good measure, we could define a final interface named IRenderToMemory, which

extends IPrintable with a new member named Render():

public interface IRenderToMemory : IPrintable

{

void Render();

}

Given this design, if a type were to implement IRenderToMemory, we would now be required to

implement each and every member defined up the chain of inheritance (specifically, the Render(),

Print(), and Draw() methods). On the other hand, if a type were to only implement IPrintable, we

would only need to contend with Print() and Draw(). For example:

public class SuperShape : IRenderToMemory

{

public void Draw()

{

Console.WriteLine("Drawing...");

}

public void Print()

{

Console.WriteLine("Printing...");

}

public void Render()

{

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