/*
对象和类
*/
//注意 self 被用来区别实例变量。当你创建实例的时候,像传入函数参数一样给类传入构造器的参数。
//每个属性都 需要赋值——无论是通过声明(就像 numberOfSides )还是通过构造器(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."
}
}
//如果你需要在删除对象之前进行一些清理工作,使用 deinit 创建一个析构函数
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()
//了储存简单的属性之外,属性可以有 getter 和 setter,在 perimeter 的 setter 中,新值的名字是 newValue
//注意 EquilateralTriangle 类的构造器执行了三步:
//1. 设置子类声明的属性值
//2. 调用父类的构造器
//3. 改变父类定义的属性值。其他的工作比如调用方法、getters和setters也可以在这个阶段完成。
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)
//如果不需要计算属性,但是仍然需要在设置一个新值之前或者之后运行代码,使用 willSet 和 didSet
//下面的类确保三角形的边长总是和正方形的边长相同
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)
//处理变量的可选值时,你可以在操作(比如方法、属性和子脚本)之前加 ? 。如果 ? 之前的值是 nil , ? 后面 的东西都会被忽略,并且整个表达式返回 nil 。否则, ? 之后的东西都会被运行。在这两种情况下,整个表达式 的值也是一个可选值。
let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square")
let sideLength = optionalSquare?.sideLength
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