Lecture Notes for Advanced Programming II

13 March 2001 - Virtual Classes

1. to review

   1. classes without inheritance are great

   2. use inheritance to get polymorphism amoung classes

   3. virtual members give useful polymorphism - search from the bottom

2. the virtual issues -

   1. what should be virtual

   2. destructors

   3. coupling

3. what should be virtual

   1. make everything virtual - but that's expensive

   2. cost in time and space

4. destructors

   1. what's the problem?

   2. non-virtual destructors in the parent class

   3. the child-class destructors can get skipped

   4. a puzzle

      1. class p {
           public:
            ~p() { cout << "delete a p.\n"; }
           };
         
         class c : public p {
           public:
             virtual ~c() { cout << "delete a c.\n"; }
           };
         
         void main(void) {
           p * pp = new c;
           delete pp;
           c * cp = new c;
           delete cp;
           }
         

      2. what's the output

5. coupling

   1. coupling is a measure of independence among modules the more coupling between two modules, the less independent they are

   2. low coupling is important - easy to create, understand, modify

   3. coupling is hard to quantify

   4. value couples less strongly than behavior - behavior is function; value is data

This page last modified on 27 February 2001.