C++ program part6

1. When should you use multiple inheritance?
   There are three acceptable answers: "Never," "Rarely," and "When the problem domain cannot be accurately modeled any other way."
   There are some famous C++ pundits and luminaries who disagree with that third answer, so be careful.
   Let's digress to consider this issue lest your interview turn into a religious debate. Consider an Asset class, Building class, Vehicle class, and CompanyCar class. All company cars are vehicles. Some company cars are assets because the organizations own them. Others might be leased. Not all assets are vehicles. Money accounts are assets. Real-estate holdings are assets. Some real-estate holdings are buildings. Not all buildings are assets. Ad infinitum. When you diagram these relationships, it becomes apparent that multiple inheritance is an intuitive way to model this common problem domain. You should understand, however, that multiple inheritance, like a chainsaw, is a useful tool that has its perils, needs respect, and is best avoided except when nothing else will do. Stress this understanding because your interviewer might share the common bias against multiple inheritance that many object-oriented designers hold.
   
   
2. What is a virtual destructor?
   The simple answer is that a virtual destructor is one that is declared with the virtual attribute.
   The behavior of a virtual destructor is what is important. If you destroy an object through a pointer or reference to a base class, and the base-class destructor is not virtual, the derived-class destructors are not executed, and the destruction might not be complete.
   
   
   
3. Explain the ISA and HASA class relationships. How would you implement each in a class design?
   A specialized class "is a" specialization of another class and, therefore, has the ISA relationship with the other class. An Employee ISA Person. This relationship is best implemented with inheritance. Employee is derived from Person. A class may have an instance of another class. For example, an Employee "has a" Salary, therefore the Employee class has the HASA relationship with the Salary class. This relationship is best implemented by embedding an object of the Salary class in the Employee class.
   The answer to this question reveals whether you have an understanding of the fundamentals of object-oriented design, which is important to reliable class design.
   There are other relationships. The USESA relationship is when one class uses the services of another. The Employee class uses an object (cout) of the ostream class to display the employee's name onscreen, for example. But if you get ISA and HASA right, you usually don't need to go any further.