The Assignment Operator

1. The Assignment Operator

2. Rule of Three • Any object which manages memory needs: • Custom Destructor • Custom Copy Constructor • Custom Assignment Operator (now)

3. Copy Constructor • Generally need a deep copy not a shallow one: YES NO

4. Copy Constructor Recipee • Basic copy constructor recipe:

5. Using Copy Ctor Explicitly • Explicit copy constructor call:

6. Using Copy Ctor Implicitly • Initialization while declaring uses copy constructor:

7. Using Assignment Operator • Assign existing object uses assignment operator

8. Default Assignment Operator • Every class gets default assignment operator • Copies each member directly: • Shallow copy!!!

9. Custom Assignment Operator • Custom assignment operator similar to copy constructor • Copy over basic information • Allocate own dynamic memory • Copy values that are in dynamic memory

10. Custom Assignment Operator • Custom assignment operator similar to copy constructor • Copy over basic information • Allocate own dynamic memory • Copy values that are in dynamic memory • Differences: • Signature : returns a object reference • Already have an object… which already owns memory • Have to watch for self assignment

11. Custom Assignment Operator • Course assignment operator: I will return a reference to the course that we are copying into I take a reference to a course we will not change Interpreted as course2.=(course1)

12. Why return reference • Chained assignments are allowed in C++ Only makes sense if y = 2 resolves to y when done

13. Why return reference • Chained assignments are allowed in C++ Only makes sense if y = 2 resolves to y when done y

14. Copy Constructor First Pass… • On assignment: • Two existing objects • Want to turn one into deep copy of other course2 = course1course2.=(other)course2 is thiscourse1 is other

15. Copy Constructor First Pass… Copy basics:

16. Copy Constructor First Pass… Delete oldstorage

17. Copy Constructor First Pass… Allocate newstorage andcopy data

18. Copy Constructor First Pass… Return theobject that wascopied into

19. Self Assignment Danger • Self assignment will clear an object / blow up your program:

20. Bad Self Assignment Copying basicinfo does nothing

21. Bad Self Assignment Deleting wipes outstorage!!!

22. Bad Self Assignment Allocate a newempty array

23. Bad Self Assignment Loop either copiesempty objectsor maybe blowsup

24. Bad Self Assignment Loop either copiesempty objectsor maybe blowsup

25. Final Version • Final version : • Compare address of self to address of otherOnly copy if not same

26. Recipe • Basic recipe:

27. Applied to ArrayList • Combine operator overloads with templates and we get a much easier to use array:

28. Vectors • Vector is C++'s official ArrayList • Programmers should use instead of arrays most of the time • We'll study week 10 • Take a peek if you want Ch 12.6-12.8