感谢Github上The Swift Programming Language开源翻译的中文版，感谢极客学院wiki提供的PDF版本
SwiftTour是对Swift主要的语言特性有个速览，后续的教程会逐个展开阐述。
代码上传至Github，有兴趣的可以下载下来试试

// 使用class和类名创建一个类 class Shape { var numberOfSides = 0 func simpleDescription() ->String { return "A Shape with \(numberOfSides) sides" } } var shape = Shape() shape.numberOfSides = 7 var shapeDescription = shape.simpleDescription() // 使用init创建构造器,使用deinit创建一个析构函数 class NameShape { var numberOfSides: Int = 0
    var name: String
    init(name: String) {
        self.name = name
    }
    func simpleDescription() ->String {
        return "A Shape with \(numberOfSides) sides"
    }
}

// 子类重写父类的方法需要用override标记
class Squre: 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 "A square with sides of length \(sideLength)"
    }
}
let test = Squre(sideLength: 5.2,name: "My test Square")
test.area()
test.simpleDescription()

// 类的getter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 triangle with sides of length \(sideLength)"
    }
}
var triangel = EquilateralTriangle(sideLength: 3.1,name: "a triangle")
print(triangel.perimeter)
triangel.perimeter = 9.9
print(triangel.sideLength)

// 不需要计算属性，仍然需要在设置新值之前或之后运行代码，使用willset和didset
// 确保三角形的边长综合正方形的边长相同
class TriangleAndSquare { var triangle: EquilateralTriangle {
        willSet {
            square.sideLength = newValue.sideLength
        }
    }
    var square: Squre {
        willSet {
            triangel.sideLength = newValue.sideLength
        }
    }
    init(size: Double,name: String) {
        square = Squre(sideLength: size,name: name)
        triangle = EquilateralTriangle(sideLength: size,name: name)
    }
}
var triangleAndSquare = TriangleAndSquare(size: 10,name: "Another tested Shape")
print(triangleAndSquare.square.sideLength)
print(triangleAndSquare.triangle.sideLength)
triangleAndSquare.triangle = EquilateralTriangle(sideLength: 30,name: "Other")
print(triangleAndSquare.triangle.sideLength)
print(triangleAndSquare.square.sideLength)

// 处理变量的可选值时，可以在操作前加？
let optionalSquare: Squre? = Squre(sideLength: 2.5,name: "Optional square")
let sideLength = optionalSquare?.sideLength
print(sideLength)