1. Virtual Functions & Polymorphism

2. Geometric Object Example Function also available in Circle & Rectagle Circle & Rectangle could use toString() but chose to override

3. Dispatch Normal functions only use "obvious" version of function:

4. Virtual Functions virtual function If you are trying to use this behavior, first check for a new version in any subtypes I am

5. Virtual Functions Everything else the same…

6. Polymorphism Polymorphism : many forms – Ability of one function call to produce different results depending on exact type of object

7. Virtual Lookup On toString() call… – We know we have a GeometricObject Could use that toString() GeometricObj& Geometric Object Circle ?

8. Virtual Lookup On toString() call… – We know we have a GeometricObject Could use that toString() – But since virtual, go look for other version GeometricObj& Geometric Object Circle !!

9. VTables Vtable : Table of function pointers – Objects have pointer to vtable for their class

10. VTables Virtual Dispatch: – Start with object pointer

11. VTables Virtual Dispatch: – Look up vtable address for this object

12. VTables Virtual Dispatch: – Look up function address for desired function

13. VTables Virtual Dispatch: – Start with object pointer – Look up vtable address for this object – Look up function address for desired function – Call that function Normal Dispatch: – Call the function

14. Virtual Advice Virtual tips: – Use anytime child class may need to change behavior of a function – Slight overhead to vtable lookup

15. Virtual Advice Virtual tips: – Declare function virtual in parent.h – No changes to.cpp – Do not have to declare as virtual in child classes

16. Other modifiers C++11 adds override and final – Final : Child classes cannot provide new versions – Override : Make sure I am actually overriding a parent function

17. Last Virtual Tip Classes that are inherited from should declare virtual destructor GeometricObject* gp = //mystery pointer delete GeometricObject; If virtual – go see if we have child destructor to call If NOT virtual – only use GeometricObject's destructor