Hiding Unnecessary Information from the class User
That rule applies only to functions that are accessible to the user of the polymorphic object. The GetType function is intended for use only in the implementation of the polymorphic object, not by its users; therefore, it is not only possible but desirable to keep it “hidden” by declaring it inside one of the worker classes. Because the user never creates an object of any of the worker classes directly, declaring a function in one of those classes has much the same effect as making it a private member function. As we have already seen, hiding as many implementation details as possible helps to improve the robustness of our programs.
I should also mention the different data types for member variables ...
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