[swift] Class 상속

import UIKit


struct Grade {
    var letter: String
    var points: Double
    var credits: Double
}


class Person {
    var firstName: String
    var lastName: String
    
    init(firstName: String, lastName: String) {
        self.firstName = firstName
        self.lastName = lastName
    }
    
    func printMyName() {
        print("My name is \(firstName) \(lastName)")
    }
}

class Student {
    var firstName: String
    var lastName: String
    var grades: [Grade] = []
    
    init(firstName: String, lastName: String) {
        self.firstName = firstName
        self.lastName = lastName
    }
    
    func printMyName() {
        print("My name is \(firstName) \(lastName)")
    }
    
    func recordGrade(_ grade: Grade){
        grades.append(grade)
    }
}

person과 student가 중복되는 부분이 많음.

개발하면서 제일 피해야하는 것이 중복

중복은 상속(inheritence)으로 해결할 수 있다.

 

상속하는 방법 :Person

class Person {
    var firstName: String
    var lastName: String
    
    init(firstName: String, lastName: String) {
        self.firstName = firstName
        self.lastName = lastName
    }
    
    func printMyName() {
        print("My name is \(firstName) \(lastName)")
    }
}

class Student: Person{
 
    var grades: [Grade] = []
    
    //Person이 쓰는 initializer 그대로 사용 가능
    
    //Person이 쓰는 함수도 그대로 사용 가능
    
    func recordGrade(_ grade: Grade){
        grades.append(grade)
    }
}

 

상속(inheritence)

Person : Base Class (Super Class, Parent Class)

Student: SubClass

- 1개의 Base Class만 상속 받을 수 있음

- 상속의 깊이는 상관 없음

 

class StudentAthlete: Student{
    var minimumTrainingTime: Int = 2
    var trainedTime: Int = 0
    
    func train(){
        trainedTime += 1
    }
}

class FootballPlayer: StudentAthlete {
    var footballTeam = "FC Swift"
    
    //override -> StudentAthlete 에서 정의된 함수에 기능 추가
    override func train() {
        trainedTime += 2
    }
}

var athlete1 = StudentAthlete(firstName: "yuna", lastName: "kim")
athlete1.trainedTime
athlete1.train() //train을 하고 나면 1시간 증가
athlete1.trainedTime

var athlete2 = FootballPlayer(firstName: "HM", lastName: "Son")
athlete2.trainedTime
athlete2.train()
athlete2.trainedTime
athlete2.footballTeam

 

 

✍️ upper casting  ( 자식 -> 부모 )     as

StudentAthlete으로 타입캐스팅했는데 왜 +2가되는지 모르겠다.

타입캐스팅을 했는데도 FootballPlayer의 오버라이드된 train()함수가 작동하는거같다.

 

✍️ down casting  ( 부모 -> 자식 )

 

될지 안될지 모르므로 ?를 붙여준다. = Optional타입으로 나온다

-> if let으로 바인딩

 

import UIKit


struct Grade {
    var letter: String
    var points: Double
    var credits: Double //학점
}


class Person {
    var firstName: String
    var lastName: String
    
    init(firstName: String, lastName: String) {
        self.firstName = firstName
        self.lastName = lastName
    }
    
    func printMyName() {
        print("My name is \(firstName) \(lastName)")
    }
}

class Student: Person{
 
    var grades: [Grade] = []
    
    //Person이 쓰는 initializer 그대로 사용 가능
    
    //Person이 쓰는 함수도 그대로 사용 가능
    
    func recordGrade(_ grade: Grade){
        grades.append(grade)
    }
}

let puang = Person(firstName: "Puang", lastName: "Lee")
let yj = Student(firstName: "yj", lastName: "kim")

puang.firstName
yj.firstName


//puang.printMyName()
//yj.printMyName() //상속받은 함수가 잘 작동함


let math = Grade(letter: "B", points: 8.5, credits: 3.0)
let history = Grade(letter: "A+", points: 10.0, credits: 4.0)

yj.recordGrade(math)
yj.recordGrade(history)
yj.grades.count


class StudentAthlete: Student{
    var minimumTrainingTime: Int = 2
    var trainedTime: Int = 0
    
    func train(){
        trainedTime += 1
    }
}

class FootballPlayer: StudentAthlete {
    var footballTeam = "FC Swift"
    
    //override -> StudentAthlete 에서 정의된 함수에 기능 추가
    override func train() {
        trainedTime += 2
    }
}

var athlete1 = StudentAthlete(firstName: "yuna", lastName: "kim")
athlete1.trainedTime
athlete1.train() //train을 하고 나면 1시간 증가
athlete1.trainedTime

var athlete2 = FootballPlayer(firstName: "HM", lastName: "Son")
athlete2.trainedTime
athlete2.train()
athlete2.trainedTime
athlete2.footballTeam


func printFirstName(_ person: Person) {
    print("---> first name: \(person.firstName)")
}

//Person -> Student -> StudentAthlete -> FootballPlayer
//Person 클래스를 상속받고있기 때문에 가능
printFirstName(athlete1)
printFirstName(yj)


//athlete1: StudentAthlete, athlete2:FootballPlayer
//자식의 타입을 부모타입으로 type casting
athlete1 = athlete2 as StudentAthlete

athlete1.lastName
athlete1.train()
athlete1.trainedTime
//athlete1.footballTeam
//athlete1의 타입이 StudentAthlete이기 때문


//StudentAthlete -> FootballPlayer 로 다운캐스팅
if let son = athlete1 as? FootballPlayer {
    print("---> name: \(son.lastName), team: \(son.footballTeam)")
}