//使用class 和類名來創(chuàng)建一個類愧捕，類中屬性的聲明和常量酌泰，變量聲明一樣荠察，唯一的區(qū)別就是它們的上下文是類，同樣，方法和函數(shù)聲明也一樣
    class Shape {
        
        var numberOfSides = 0
        func simpleDescription() -> String {
            return "A shap with \(numberOfSides) sides."
        }
        
    }

    //要創(chuàng)建一個類的實(shí)例，在類后面加上括號，使用點(diǎn)語法來訪問實(shí)例的屬性和方法
    let shape = Shape()
    shape.numberOfSides = 7
    let shapeDescription = shape.simpleDescription()
    
    print(shapeDescription)
    
    
    //使用init來創(chuàng)建一個構(gòu)造器
    class NameShape {
    
        var numberOfSides:NSInteger = 0
        var name : String
        init(name:String) {
            self.name = name
        }
        
        func simpleDescription() -> String {
            
            return "A shape with \(numberOfSides) \(name) sides."
            
        }
        
    }
    //注意self被用來區(qū)別實(shí)例變量壶冒，當(dāng)你創(chuàng)建實(shí)例的時候，像傳入函數(shù)參數(shù)一樣給類傳入構(gòu)造器的參數(shù)截歉，每個屬性都需要賦值-無論是通過聲明（就像numberOfSides   還是通過構(gòu)造器）
    let nameShape = NameShape(name:"hello")
    nameShape.numberOfSides = 10
    let nameshapeDis = nameShape.simpleDescription()
    print(nameshapeDis)
    
    
    //如果需要在刪除對象之前進(jìn)行一些清理工作胖腾，使用deinit創(chuàng)建一個析構(gòu)函數(shù)。子類的定義方法是在它們的類名后面加上父類的名字怎披，用冒號分割胸嘁。創(chuàng)建類的時候并不需要一個標(biāo)準(zhǔn)的根類，所以你可以忽略父類凉逛。子類如果要重寫父類的方法的話，需要用override標(biāo)記--如果沒有添加override就重寫父類方法的話編譯器會報錯群井，編譯器同樣會檢測override標(biāo)記的方法是否確實(shí)在父類中
    class Square:NameShape {
    
        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 "B square with sides of length \(sideLength)"
        }
    }
    
    let test = Square(sideLength:5.2,name:"my test squate")
    
    print(test.area(),test.simpleDescription())
    
    
    //除了儲存簡單的屬性之外状飞，屬性可以有g(shù)etter 和 setter 。
    class EquilateralTriangle:NameShape {
    
        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)
    
    //在perimeter 的 setter 中书斜，新值得名字是newValue诬辈。你可以在set之后顯示的設(shè)置一個名字
    //注意 EquilateralTriangle，類的構(gòu)造器執(zhí)行了三步：1荐吉，設(shè)置子類聲明的屬性值焙糟，2：調(diào)用父類的構(gòu)造器，3:改變父類定義的屬性值样屠。其他的工作比如調(diào)用方法穿撮，getters和setters也可以在這個階段完成。
    
    //如果不需要計(jì)算屬性痪欲，但是任然需要在設(shè)置一個新值之前或者之后運(yùn)行代碼悦穿，使用willSet和didSet。
    //比如业踢，下面的類確保三角形的邊長總是和正方形的邊長相同
    
    class TriangleAndSuqare {
    
        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)
        }
        
    }
    
    let triangleAndSquare = TriangleAndSuqare(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栗柒，可以在操作（比如方法，屬性知举，和子腳本）之前加瞬沦？，如果雇锡？之前的值是nil逛钻，？后面的東西都會被忽略遮糖，并且整個表達(dá)式返回nil绣的，否則，？之后的東西都會被運(yùn)行屡江，在這兩種情況下芭概，整個表達(dá)式的值也是一個可選值
    let optionalSquare:Square? = Square(sideLength:2.5,name:"optional square")
    let sideLength = optionalSquare?.sideLength
    
    print(sideLength ?? 2)