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()
Geometric Object
Circle ?
GeometricObj&

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

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: Normal 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