C# 0 The Complete Reference

PART I

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PART IPART I

    // X references know only about X members

    x2.a = 19; // OK

//    x2.b = 27; // Error, X doesn't have a b member

  }

}

In this program, 

Y

 is derived from 

X

. Now, the assignment

x2 = y; // OK because Y is derived from X

is permissible because a base class reference, 

x2

 in this case, can refer to a derived class 

object (which is the object referred to by 

y

).

It is important to understand that it is the type of the reference variable—not the type of 

the object that it refers to—that determines what members can be accessed. That is, when a 

reference to a derived class object is assigned to a base class reference variable, you will 

have access only to those parts of the object defined by the base class. This is why