/*
對(duì)象和類
*/
//注意 self 被用來(lái)區(qū)別實(shí)例變量赘风。當(dāng)你創(chuàng)建實(shí)例的時(shí)候,像傳入函數(shù)參數(shù)一樣給類傳入構(gòu)造器的參數(shù)雁佳。
//每個(gè)屬性都 需要賦值——無(wú)論是通過(guò)聲明(就像 numberOfSides )還是通過(guò)構(gòu)造器(就像 name )
class Shape {
var numberOfSides = 0
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()
class NamedShape {
var numberOfSides: Int = 0
var name: String
init(name: String) {
self.name = name
}
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
//如果你需要在刪除對(duì)象之前進(jìn)行一些清理工作,使用 deinit 創(chuàng)建一個(gè)析構(gòu)函數(shù)
class Square: NamedShape {
var sideLength: Double
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 4
}
func area() ->? Double {
return sideLength * sideLength
}
override func simpleDescription() -> String {
return "A square with sides of length \(sideLength)."
} }
let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()
//了儲(chǔ)存簡(jiǎn)單的屬性之外,屬性可以有 getter 和 setter,在 perimeter 的 setter 中,新值的名字是 newValue
//注意 EquilateralTriangle 類的構(gòu)造器執(zhí)行了三步:
//1. 設(shè)置子類聲明的屬性值
//2. 調(diào)用父類的構(gòu)造器
//3. 改變父類定義的屬性值。其他的工作比如調(diào)用方法姻灶、getters和setters也可以在這個(gè)階段完成。
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")
print(triangle.perimeter)
triangle.perimeter = 9.9
print(triangle.sideLength)
//如果不需要計(jì)算屬性,但是仍然需要在設(shè)置一個(gè)新值之前或者之后運(yùn)行代碼,使用 willSet 和 didSet
//下面的類確保三角形的邊長(zhǎng)總是和正方形的邊長(zhǎng)相同
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")
print(triangleAndSquare.square.sideLength)
print(triangleAndSquare.triangle.sideLength)
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
print(triangleAndSquare.triangle.sideLength)
//處理變量的可選值時(shí),你可以在操作(比如方法、屬性和子腳本)之前加 ? 宝当。如果 ? 之前的值是 nil , ? 后面 的東西都會(huì)被忽略,并且整個(gè)表達(dá)式返回 nil 。否則, ? 之后的東西都會(huì)被運(yùn)行胆萧。在這兩種情況下,整個(gè)表達(dá)式 的值也是一個(gè)可選值庆揩。
let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square")
let sideLength = optionalSquare?.sideLength
