Object Oriented Programming in Swift Ch1 - Inheritance

1. Object Oriented Programming
in Swift
Ch 1: Inheritance
Sai Li @ Yowoo Tech.
2016/12/5

2. References
• Agile Software Development: Principles, Patterns,
and Practice ( : )
by Robert C. Martin
• Fundamental Object Oriented Programming
by Hsuan-Tien Lin
•
by Teddy Chen
• Essential Object-Oriented Programming
by Josh Ko

3. OOP
• Encapsulation
• Inheritance
• Polymorphism

4. Spaghetti
v.s
Ravioli

5. Inheritance

6. Has-A
• Has-A: a basic way to reuse variables/methods
in other classes

7. Has-A
• Has-A: a basic way to define components of a system
• iPhone has a camera

8. Has-A
• Has-A: a basic mechanism for
objects to connect with each other
• He has 2 friends: Tom and Jerry

9. Has-A: most basic design component of OOP

10. chi
• Admin is a user
• can be implemented via has-a:
Everyone has Brokeback Mountain in mind
child

11. • Type A inherit TypeB: TypeA is a (special case of) TypeB
• TypeSubClass (TypeDerivedClass or ChildClass) inherit
TypeSuperClass (TypeBaseClass or ParentClass)

12. is-a != has-a

13. Uses of Is-A
• CDAndCassetePlayer is a CassettePlayer

14. Uses of Is-A
• CassettePlayer is a (concrete type of) Player
• CDPlayer is a (concrete type of) Player

15. Uses of Is-A
• CDplayer is a (update of) CassettePlayer
• some behaviors “changed”
• no as clear as the previous case, but a potential trick
in OOP

16. • Multiple inheritance: Not supported in Swift
• Swift: single inheritance (Java)

17. Diamond Problem
?

18. Diamond Problem

19. Is-A
• is an extended type of
- FunPerson is Person who can tell jokes
• is a more concrete/restricted description of
- YoungPerson is Person who is young
• (is an update of)
- NewStaff replaces ExistingStaff

21. • Over-use of inherit for is-a: 1 class -> 1 instance
• Usual goal of OOP: one class, many instances

22. Is-A
• Under-user of inherit for is-a: overly complicated class
YowooStaff
• Bugs/hacks?
cali = YowooStaff(id: “”, name: “CYLi”, title: “CFO”)

23. Terminology

24. Instance Variables and Inheritance
• Staff: 1 instance variables
• YowooStaff: 2 instance variables

25. Instance Variables and Inheritance

26. • instance variable binding: determined at
compile time
• same “name” can NOT co-exist in a class,
binding determined by compile-time type.

27. Instance Methods and Inheritance
• Staff: 1 instance method
• RD: 2 instance methods

28. • what output?

29. • instance method binding: dynamic, depending
on run-time instance types

30. Reference Assignment
• saiLi is an instance of GoodStudent
• saiLi is an instance of Student, too
• one instance, many coherent types

31. Constructor and Inheritance
• initialize self first, ancestor last
• the GoodStudent part of the memory initialized first,
the Student part

32. Swift Constructor Calls
Designate
Convenience

33. Swift Constructor Calls
Parent
Child

34. Private Variables and Inheritance

35. private variables are still “inherited” in
memory, but not “visible” to the subclass
because of encapsulation (security)

36. • protected: accessible to Child(subclass)

37. • public: everyone
• internal (default): same package classes
• protected: sub-classes
• private: class self
Swift Access Permissions

38. Access Permission (Swift)
• Child: same or more close than Parent

39. References
• Apple: Access Control and protected
• http://commons.oreilly.com/wiki/images/a/a7/
Beyond_Java_I_2_tt13.png
• https://upload.wikimedia.org/wikipedia/commons/
thumb/4/47/C3_linearization_example.svg/600px-
C3_linearization_example.svg.png
• https://developer.apple.com/library/content/
documentation/Swift/Conceptual/
Swift_Programming_Language/Art/
initializerDelegation02_2x.png