Swift Objects and Classes #2 - Properties getter setter

- Properties

properties는 getter와 setter를 가진다.

class NamedShape {

    var numberOfSides: Int = 0

    var name: String

    

    init(name: String) {

        self.name = name

    }

    

    func simpleDescription() -> String {

        return "A shape with \(numberOfSides) sides."

    }

}

class EquilateralTriangle: NamedShape {

    var sideLength: Double = 0.0

    

    init(sideLength: Double, name: String) {

        self.sideLength = sideLength

        super.init(name: name)

        numberOfSides = 3

    }

    

    var perimeter: Double {

    get {

        return 3.0 * sideLength

    }

    set {

        sideLength = newValue / 3.0

    }

    }

    

    override func simpleDescription() -> String {

        return "An equilateral triagle with sides of length \(sideLength)."

    }

}

var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")

triangle.perimeter

triangle.perimeter = 9.9

triangle.sideLength

perimeter속성에서 setter는 newValue라는 키워드로 값을 표현한다. 

이것은 set후에 {}안에서 사용될 수 있다.

willSet, didSet을 사용하면 값을 설정하기 전이나 설정한 후에 원하는 추가 작업을 수행할

수 있다.

예1)

class TriangleAndSquare {

    var triangle: EquilateralTriangle {

    willSet {

        square.sideLength = newValue.sideLength

    }

    }

    var square: Square {

    willSet {

        triangle.sideLength = newValue.sideLength

    }

    }

    init(size: Double, name: String) {

        square = Square(sideLength: size, name: name)

        triangle = EquilateralTriangle(sideLength: size, name: name)

    }

}

var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")

triangleAndSquare.square.sideLength

triangleAndSquare.triangle.sideLength

triangleAndSquare.square = Square(sideLength: 50, name: "larger square")

triangleAndSquare.triangle.sideLength

예2)

class StepCounter {

    var totalSteps: Int = 0 {

        willSet(newTotalSteps) {

            println("[willSet] 호출, 새로운 값: \(newTotalSteps)")

        }

        didSet {

            println("[didSet] 호출")

            if totalSteps > oldValue {

                println("Added \(totalSteps - oldValue) steps")

            }

        }

    }

}

let stepCounter = StepCounter()

stepCounter.totalSteps = 200

stepCounter.totalSteps = 360

stepCounter.totalSteps = 896

/*

[willSet] 호출, 새로운 값: 200

[didSet] 호출

Added 200 steps

[willSet] 호출, 새로운 값: 360

[didSet] 호출

Added 160 steps

[willSet] 호출, 새로운 값: 896

[didSet] 호출

Added 536 steps

*/