Object Oriented Programming in Swift

Ch 1: Inheritance

Sai Li @ Yowoo Tech. 2016/12/5

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 Programmingby Josh Ko

OOP

• Encapsulation • Inheritance• Polymorphism

Spaghetti

v.s

Ravioli

Inheritance

Has-A

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

Has-A

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

Has-A

• Has-A: a basic mechanism for objects to connect with each other

• He has 2 friends: Tom and Jerry

Has-A: most basic design component of OOP

chi

• Admin is a user • can be implemented via has-a:

Everyone has Brokeback Mountain in mindchild

• Type A inherit TypeB: TypeA is a (special case of) TypeB • TypeSubClass (TypeDerivedClass or ChildClass) inherit

TypeSuperClass (TypeBaseClass or ParentClass)

is-a != has-a

Uses of Is-A

• CDAndCassetePlayer is a CassettePlayer

Uses of Is-A

• CassettePlayer is a (concrete type of) Player • CDPlayer is a (concrete type of) Player

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

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

Diamond Problem

?

Diamond Problem

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

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

Is-A

• Under-user of inherit for is-a: overly complicated class YowooStaff

• Bugs/hacks?cali = YowooStaff(id: “”, name: “CYLi”, title: “CFO”)

Terminology

Instance Variables and Inheritance

• Staff: 1 instance variables • YowooStaff: 2 instance variables

Instance Variables and Inheritance

• instance variable binding: determined at compile time

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

Instance Methods and Inheritance

• Staff: 1 instance method • RD: 2 instance methods

• what output?

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

Reference Assignment

• saiLi is an instance of GoodStudent • saiLi is an instance of Student, too • one instance, many coherent types

Constructor and Inheritance

• initialize self first, ancestor last• the GoodStudent part of the memory initialized first,

the Student part

Swift Constructor Calls

Designate

Convenience

Swift Constructor Calls

Parent

Child

Private Variables and Inheritance

private variables are still “inherited” in memory, but not “visible” to the subclass

because of encapsulation (security)

• protected: accessible to Child(subclass)

• public: everyone

• internal (default): same package classes

• protected: sub-classes

• private: class self

Swift Access Permissions

Access Permission (Swift)

• Child: same or more close than Parent

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