1. Aggregation

2. Pointer Uses Objects need pointers for: Dynamic Memory Sharing Objects
Need to create data on heap and have pointers to it
Sharing Objects
Want two things to know about same "Bob"

3. A riddle… Bob, Candace, Ernie and Sue are People
Ernie and Sue are Childs
Both are children of Bob and Candace
How many people are there named Bob?

4. 3 Child Versions Plain Old Variable Version
Father/mother are Person objects

5. Plain Old Explored
Child has their own Person as parent

6. 3 Child Versions Plain Old Variable Version
Father/mother are objects that exist within Child
Each Child has own copies of father/mother

7. 3 Children Versions
Pointer Version
father/mother pointers to Person

8. Plain Old Explored
Child points to a shared parent

9. 3 Children Versions Pointer Version
Father/mother are pointers to external objects
Parent's shared… probably not owned

10. 3 Child Versions
References Version
Can share with reference vars:

11. 3 Children Versions ReferenceVersion Fussy
No way to change parent later
Definitely not owned

12. Ownership
General rules of thumb:
Plain Variable
Owns memory it labels

13. Ownership General rules of thumb: Plain Variable Owns memory it labels
Reference Variable
Does not own memory of thing it references

14. Ownership General rules of thumb: Plain Variable Owns memory it labels
Reference Variable
Does not own memory of thing it references
Pointer
May or may not own memory Only one pointer can

15. UML Aggregation vs Compostion
Composition : has-a built using other object, object only exists as part of this one
C++ standard variable

16. UML Aggregation vs Compostion
Aggregation : has-a built using other object, but not necessarily owned
C++ pointer/reference

17. Class vs Object Diagrams
Class Diagram: Object Diagram: 1 box per class box per object

18. Self-Reference
C++ does not allow self-composition

19. Self-Reference
Self-Aggregation is perfectly fine:

20. Self-Reference
Class: Objects: