swift菜鸟教程26-27（类型转换，拓展)

今日学习内容：

1.Swift 类型转换： is 和 as 操作符实现，is 用于检测值的类型，as 用于转换类型。

1.1检查类型

class Subjects {
    var physics: String
    init(physics: String) {
        self.physics = physics
    }
}

class Chemistry: Subjects {
    var equations: String
    init(physics: String, equations: String) {
        self.equations = equations
        super.init(physics: physics)
    }
}

class Maths: Subjects {
    var formulae: String
    init(physics: String, formulae: String) {
        self.formulae = formulae
        super.init(physics: physics)
    }
}

let sa = [
    Chemistry(physics: "固体物理", equations: "赫兹"),
    Maths(physics: "流体动力学", formulae: "千兆赫"),
    Chemistry(physics: "热物理学", equations: "分贝"),
    Maths(physics: "天体物理学", formulae: "兆赫"),
    Maths(physics: "微分方程", formulae: "余弦级数")]


let samplechem = Chemistry(physics: "固体物理", equations: "赫兹")
print("实例物理学是: \(samplechem.physics)")
print("实例方程式: \(samplechem.equations)")


let samplemaths = Maths(physics: "流体动力学", formulae: "千兆赫")
print("实例物理学是: \(samplemaths.physics)")
print("实例公式是: \(samplemaths.formulae)")

var chemCount = 0
var mathsCount = 0
for item in sa {
    // 如果是一个 Chemistry 类型的实例，返回 true，相反返回 false。
    if item is Chemistry {
        ++chemCount
    } else if item is Maths {
        ++mathsCount
    }
}

print("化学科目包含 \(chemCount) 个主题，数学包含 \(mathsCount) 个主题")
以上程序执行输出结果为：

实例物理学是: 固体物理
实例方程式: 赫兹
实例物理学是: 流体动力学
实例公式是: 千兆赫
化学科目包含 2 个主题，数学包含 3 个主题

1.2向下转型

let sa = [
    Chemistry(physics: "固体物理", equations: "赫兹"),
    Maths(physics: "流体动力学", formulae: "千兆赫"),
    Chemistry(physics: "热物理学", equations: "分贝"),
    Maths(physics: "天体物理学", formulae: "兆赫"),
    Maths(physics: "微分方程", formulae: "余弦级数")]


let samplechem = Chemistry(physics: "固体物理", equations: "赫兹")
print("实例物理学是: \(samplechem.physics)")
print("实例方程式: \(samplechem.equations)")


let samplemaths = Maths(physics: "流体动力学", formulae: "千兆赫")
print("实例物理学是: \(samplemaths.physics)")
print("实例公式是: \(samplemaths.formulae)")

var chemCount = 0
var mathsCount = 0

for item in sa {
    // 类型转换的条件形式
    if let show = item as? Chemistry {
        print("化学主题是: '\(show.physics)', \(show.equations)")
        // 强制形式
    } else if let example = item as? Maths {
        print("数学主题是: '\(example.physics)',  \(example.formulae)")
    }
    
以上程序执行输出结果为：

实例物理学是: 固体物理
实例方程式: 赫兹
实例物理学是: 流体动力学
实例公式是: 千兆赫
化学主题是: '固体物理', 赫兹
数学主题是: '流体动力学',  千兆赫
化学主题是: '热物理学', 分贝
数学主题是: '天体物理学',  兆赫
数学主题是: '微分方程',  余弦级数

1.3Any 实例

// 可以存储Any类型的数组 exampleany
var exampleany = [Any]()

exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("Any 实例")
exampleany.append(Chemistry(physics: "固体物理", equations: "兆赫"))

for item2 in exampleany {
    switch item2 {
    case let someInt as Int:
        print("整型值为 \(someInt)")
    case let someDouble as Double where someDouble > 0:
        print("Pi 值为 \(someDouble)")
    case let someString as String:
        print("\(someString)")
    case let phy as Chemistry:
        print("主题 '\(phy.physics)', \(phy.equations)")
    default:
        print("None")
    }

以上程序执行输出结果为：
整型值为 12
Pi 值为 3.14159
Any 实例
主题 '固体物理', 兆赫

1.4AnyObject 实例

// [AnyObject] 类型的数组
let saprint: [AnyObject] = [
    Chemistry(physics: "固体物理", equations: "赫兹"),
    Maths(physics: "流体动力学", formulae: "千兆赫"),
    Chemistry(physics: "热物理学", equations: "分贝"),
    Maths(physics: "天体物理学", formulae: "兆赫"),
    Maths(physics: "微分方程", formulae: "余弦级数")]


let samplechem = Chemistry(physics: "固体物理", equations: "赫兹")
print("实例物理学是: \(samplechem.physics)")
print("实例方程式: \(samplechem.equations)")


let samplemaths = Maths(physics: "流体动力学", formulae: "千兆赫")
print("实例物理学是: \(samplemaths.physics)")
print("实例公式是: \(samplemaths.formulae)")

var chemCount = 0
var mathsCount = 0

for item in saprint {
    // 类型转换的条件形式
    if let show = item as? Chemistry {
        print("化学主题是: '\(show.physics)', \(show.equations)")
        // 强制形式
    } else if let example = item as? Maths {
        print("数学主题是: '\(example.physics)',  \(example.formulae)")
    }
}

2.Swift 扩展：一个扩展可以扩展一个已有类型，使其能够适配一个或多个协议

2.1计算型属性

extension Int {
   var add: Int {return self + 100 }
   var sub: Int { return self - 10 }
   var mul: Int { return self * 10 }
   var div: Int { return self / 5 }
}
    
let addition = 3.add
print("加法运算后的值：\(addition)")
    
let subtraction = 120.sub
print("减法运算后的值：\(subtraction)")
    
let multiplication = 39.mul
print("乘法运算后的值：\(multiplication)")
    
let division = 55.div
print("除法运算后的值: \(division)")

let mix = 30.add + 34.sub
print("混合运算结果：\(mix)")
以上程序执行输出结果为：

加法运算后的值：103
减法运算后的值：110
乘法运算后的值：390
除法运算后的值: 11
混合运算结果：154

2.2向类中添加新的便利构造器 init()

struct sum {
    var num1 = 100, num2 = 200
}

struct diff {
    var no1 = 200, no2 = 100
}

struct mult {
    var a = sum()
    var b = diff()
}


extension mult {
    init(x: sum, y: diff) {
        _ = x.num1 + x.num2
        _ = y.no1 + y.no2
    }
}


let a = sum(num1: 100, num2: 200)
let b = diff(no1: 200, no2: 100)

let getMult = mult(x: a, y: b)
print("getMult sum\(getMult.a.num1, getMult.a.num2)")
print("getMult diff\(getMult.b.no1, getMult.b.no2)")
以上程序执行输出结果为：

getMult sum(100, 200)
getMult diff(200, 100)

2.3向Int类型添加一个名为 topics 的新实例方法：

extension Int {
   func topics(summation: () -> ()) {
      for _ in 0..<self {
         summation() 
      }
   }
}  

4.topics({
   print("扩展模块内")       
})    
    
3.topics({
   print("内型转换模块内")       
})  
以上程序执行输出结果为：

扩展模块内
扩展模块内
扩展模块内
扩展模块内
内型转换模块内
内型转换模块内
内型转换模块内

2.4修改该实例本身

extension Double {
   mutating func square() {
      let pi = 3.1415
      self = pi * self * self
   }
}

var Trial1 = 3.3
Trial1.square()
print("圆的面积为: \(Trial1)")


var Trial2 = 5.8
Trial2.square()
print("圆的面积为: \(Trial2)")


var Trial3 = 120.3
Trial3.square()
print("圆的面积为: \(Trial3)")
以上程序执行输出结果为：

圆的面积为: 34.210935
圆的面积为: 105.68006
圆的面积为: 45464.070735

2.5添加新下标。

extension Int {
    subscript(multtable: Int) -> Int {
        var powerOf10 = 1
        var index = multtable
        while index > 0 {
            powerOf10 *= 10
            index -= 1
        }
        return (self / powerOf10) % 10
    }
}

print(12[0])     // 输出：2
print(7869[1])   // 输出：6
print(786543[2]) // 输出：5
以上程序执行输出结果为：

2
6
5

2.6向已有的类、结构体和枚举添加新的嵌套类型：

extension Int {
   enum calc
   {
      case add
      case sub
      case mult
      case div
      case anything
   }

   var print: calc {
      switch self
      {
         case 0:
            return .add
         case 1:
            return .sub
         case 2:
            return .mult
         case 3:
            return .div
         default:
            return .anything
       }
   }
}

func result(numb: [Int]) {
   for i in numb {
      switch i.print {
         case .add:
            print(" 10 ")
          case .sub:
            print(" 20 ")
         case .mult:
         print(" 30 ")
         case .div:
         print(" 40 ")
         default:
         print(" 50 ")

      }
   }
}

result([0, 1, 2, 3, 4, 7])
以上程序执行输出结果为：

 10 
 20 
 30 
 40 
 50 
 50