Section 11.4 created a commission-employee class hierarchy, in which class
BasePlusCommissionEmployee inherited from class
CommissionEmployee. The examples in that section manipulated
BasePlusCommissionEmployee objects by using references to them to invoke their methods. We aimed base-class references at base-class objects and derived-class references at derived-class objects. These assignments are natural and straightforward—base-class references are intended to refer to base-class objects, and derived-class references are intended to refer to derived-class objects. However, other assignments are possible.
In the next example, we aim a base-class reference at a derived-class object. ...