This print for content only-size & color not accurate 7" X 9-1/4" / casebound / malloy

// Error! This method is not deriving from Car!

return --Speed;

}

}

The problem here is that the static SlowDown() extension method is attempting to access the

Speed field of the Car type; however, because SlowDown() is a static member of the CarExtensions

class, Speed does not exist in this context! What is permissible, however, is to make use of the this-

qualified parameter to access all public members (and 

only the public members) of the type being

extending. Thus, the following code compiles as expected:

public static class CarExtensions

{

public static int SlowDown(this Car c)

{

// OK!

return --c.Speed;

}

}

At this point, you could create a Car object and invoke the SpeedUp() and SlowDown() methods

as follows:

static void UseCar()

{

Car c = new Car();

Console.WriteLine("Speed: {0}", c.SpeedUp());

Console.WriteLine("Speed: {0}", c.SlowDown());

}

C H A P T E R   1 3  

■

C #   2 0 0 8   L A N G U A G E   F E AT U R E S

428

8849CH13.qxd  10/2/07  12:42 PM  Page 428

---