1. The Assignment Operator

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

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:
Usually returns a reference to the object
Already have an object… which already owns memory

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++ y
Only makes sense if y = 2 resolves to y when done y

14. Assignment First Pass…
On assignment:
Two existing objects
Want to turn one into deep copy of other
course2 = course1 course2.=(other) course2 is this course1 is other

15. Flawed first attempt…
Copy basic stuff

16. Flawed first attempt…
Delete old storage

17. Flawed first attempt…
Allocate new storage

18. Flawed first attempt…
Copy data

19. Flawed first attempt…
Return the object that was copied into

20. Self Assignment Danger
Flaw : self assignment deletes data

21. Bad Self Assignment
Copying basic info does nothing

22. Bad Self Assignment
Deleting wipes out storage!!!

23. Bad Self Assignment
Allocate a new empty array

24. Bad Self Assignment
Loop either copies empty data or blows up array up

25. Final Version Avoid modifying on self assignment:
If address of other is same as this (my address), don't copy

26. Recipe Basic recipe: Step Pseudocode Verify not self assigning
Copy basics
Delete old memory Make new array
Copy array
No matter what, return self
if( this != &other) {
this.size = other.size
… delete [] array
array = new whatever[other.size]
for(i = 0 to other.size -1) array[i] = other.array[i] }
return *this

27. Rule of 3 If you manage memory you need: Custom Destructor
Custom Copy Constructor
Custom Assignment Operator

28. Rule of 5 If you manage memory you need: You may want to provide:
Custom Destructor
Custom Copy Constructor
Custom Assignment Operator
You may want to provide:
Move assignment operator
Move copy constructor

29. Move semantics
C++ allows us to specify that data should be moved from one place to another:

30. Moving
Copy:

31. Moving
Copy:

32. Moving
Copy:

33. Moving
Move:

34. Moving
Move:

35. Moving
Move:

36. Defining && = Rvalue reference
Move constructor/assignment take rvalue reference:
Move constructor:

37. Defining && = Rvalue reference
Move constructor/assignment take rvalue reference:
Move assignment: