#学习笔记#Swift中Class的声明与运用

import Foundation

class NamedShape {
    var numberOfSides: Int = 0
    var name: String

    init(name: String) {
        self.name = name
    }

    func simpleDescription() ->String {
        return "A shape with \(numberOfSides) sides."
    }
}

// 注意这里的对象初始，需要传递name的属性数值进去
// 初始的时候一定要写上“name:“，否则编译器会认为没有进行初始化工作
var shape = NamedShape(name: "Bob")

// 下面是继承类的声明与使用
class Square: NamedShape {
    var sideLength: Double

    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        // 由于name属性是通过父类初始函数初始化的
        // 所以必须调用父类的init方法初始化name属性
        super.init(name: name)
        // 可以直接使用父类属性
        numberOfSides = 4
    }

    func area() -> Double {
        return sideLength * sideLength
    }

    // 重载父类方法，一定要写明override，否则编译器会报错
    override func simpleDescription() ->String {
        return "A square with sides of length \(sideLength)."
    }
}

let test = Square(sideLength: 5.2, name: "my test squre")
println(test.area())
println(test.simpleDescription())

以下是getter和setter的用法示例

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 quilateral triagle with side of length \(sideLength)"
    }
}

var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
println(triangle.perimeter)
triangle.perimeter = 9.9
println(triangle.sideLength)

以下是介绍类模块中willSet和didSet的用法，这部分比较特别
willSet可以在设置新的属性值之前运行，下面的示例是保证triangle和square的sideLength始终保持相等

class TriangleAndSquare {
    var square: Square {
    willSet {
        triangle.sideLength = newValue.sideLength
    }
    }

    var triangle: EquilateralTriangle {
    willSet {
        square.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")
println(triangleAndSquare.square.sideLength)
println(triangleAndSquare.triangle.sideLength)
// 如果是直接改变square中的sideLength的值，那么triangle中的sideLength是不会发生变化的
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
println(triangleAndSquare.triangle.sideLength)

类和结构体的主要区别是，结构体是值传递(依靠值的复制进行代码内部的传递），类是引用传递