Chapter 10 Virtual functions and polymorphism

1. With virtual functions and polymorphism, it becomes possible to design and 
   implement systems that are more easily extensible. Programs can be written 
   to process objects of types that may not exist when the program is under 
   development.

2. Polymorphic programming with virtual functions can eliminate the need for 
   switch logic. The programmer can use the virtual function mechanism to perform
   the equivalent logic automatically, thus avoiding the kinds of errors 
   typically associated with switch logic. Client code making decisions about 
   object types and representations indicates poor class design.

3. Derived classes can provide their own implementations of a base class virtual 
   function if necessary, but if they do not, the base class's implementation is 
   used.

4. C++ enables polymorphism -- the ability for objects of different classes 
   related by inheritance to respond differently to the same function call.

5. Polymorphism is implemented via virtual functions.

6. Through the use of virtual functions and polymorphism, one member function call
   can cause different actions depending on the type of object receiving the call.

7. When a base class provides a virtual member function, derived classes can 
   override the virtual function, but they do not have to override it. Thus a 
   derived class can use a base class's version of a virtual member function, 
   and this would be indicated in the vtable.

8. Polymorphism as implemented with virtual functions and dynamic binding is 
   efficient.

9. Virtual functions and dynamic binding enable polymorphic programming as 
   opposed to switch logic programming.

10. An interesting consequence of using virtual functions and polymorphism is 
    that programs take on a simplified appearance. They contain less branching 
    logic in favor of simpler sequential code. This facilitates testing, 
    debugging, program maintenance and bug avoidance.

11. When a derived class chooses not to define a virtual function, the derived 
    class simply inherits its immediate base class's virtual function definition.

12. With virtual functions and polymorphism, the programmer can deal in 
    generalities and let the execution-time environment concern itself with the 
    specifics. The programmer can command a wide varirty of objects to behave 
    in manners appropriate to those objects without even knowing the types of 
    those objects.

13. Polymorphism promotes extensibility: software written to invoke polymorphic 
    behavior is written independently of the types of the objects to which 
    messages are sent. Thus  new types of objects that can respond to existing 
    messages can be added into such a system without modifying the base system. 
    Except for client code that instantiates new objects, programs need not be 
    recompiled.