"Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it."
This means that all of the derived classes should retain the existing behavior of the base class as expected by the client while extending the functionality as fulfilled by the parent class. This also means that the client code that consumes a specific class or interface should be able to use a derived class or a different implementation of the interface without affecting or having to change its internal behavior, which ultimately minimizes the impact on the consumer code as a result of a change added by the derived class.
Let's demonstrate this principle with an example. We create ...
