变态的枚举类型-Swift的变化

一 .枚举基本的写法和使用

enum Month {
    case January
    case February
    case March
    case April
    case May
    case June
    case July
    case Auguest
    case September
    case October
    case November
    case December
}

print(Month.January)

let curMonth = Month.July

/**
 有限值 枚举是一种新的类型
 */
func season(month:Month) -> String {
    
    switch month {
    case Month.March,Month.April,Month.May:
        return "Spring"
    case Month.June,Month.July,Month.Auguest:
        return "Summer"
    case Month.September,Month.October,Month.November:
        return "Autumn"
    case .December,Month.January,Month.February:
        return "Spring"
//    default:
//        return "Not valid"
    }
    /**
     *  枚举类型的话,可以被穷举 ,Default 可以去掉
     */
}

二 .枚举与原始值

enum Month :Int{
    case January = 1
    case February
    case March
    case April
    case May
    case June
    case July
    case Auguest
    case September
    case October
    case November
    case December
}


print(12-Month.January.rawValue)

let curMonth = Month.July

func monthsBeforeNewYear(month:Month) -> Int {
    return 12 - month.rawValue
}

let input = 11;
let month = Month(rawValue: input) // int  类型 和 枚举类型之间的转化  //返回值是一个可选型

if let month = month{  //解包操作
   monthsBeforeNewYear(curMonth)
}

// 枚举 和原始值得简写
enum Grade:Int{
    case F,E,D,C,B,A
}

let grade:Grade = .A
print("Your score is \(grade.rawValue)")


// 枚举原始值 可以不按顺序  这种写法给了我们很大的使用空间
enum Coin:Int {
    case Penny = 1
    case Nickel = 5
    case Dime = 10
    case Quarter = 25
}

let coin:Coin = .Quarter
print("It's \(coin.rawValue) cents")


// 枚举原始值 可以默认推导
enum ProgrammingLanguage:String {
    case Swift
    case ObjectiveC = "Objective-C"
    case C
    case Java
}

let myFavoriteLanguage:ProgrammingLanguage = .ObjectiveC
print("\(myFavoriteLanguage.rawValue) is my FavoriteLanguage")

三,枚举中 关联数值的使用 有多态既视感的运用,炫酷

// Associate Value  原始值 和 关联值 不能同时设置

enum ATMStatus {
    case Success(Int)
    case Error(String)
    case Warning  //也可以不设置关联值
}



var balance = 1000

func withdraw(amount:Int)->ATMStatus{
    if balance >= amount{
        balance -= amount
        return .Success(balance)
    }else{
        return .Error("Not enough money")
    }
}

let result = withdraw(10000) //表示提款 100


/**
 *  解析值 不是必须的.
 */
switch result{
case let .Success(newBalance):  //这里 有一个解包的过程  值会放在newBalance 中,新语法
    print("\(newBalance) Yan left in you account")
case let .Error(errorMessge):
    print("Error:\(errorMessge)")
case .Warning:
    print("Warning")
}

/**
 *  不解析
 */
switch result{
case .Success:
    print("Success")
case .Error:
    print("Error")
case .Warning:
    print("Warning")
}


/**
 
 枚举类型 关联多个值 的一个应用, 有那种多态的既视感
 */

enum Shape {
    case Square(side:Double)
    case Rectangle(width:Double,height:Double)
    case Circle(centerx:Double,centery:Double,radius:Double)
    case Point
}



let square = Shape.Square(side: 10)
let rectangel = Shape.Rectangle(width: 20, height: 30)
let circle = Shape.Circle(centerx: 0, centery: 0,radius: 10)
let point = Shape.Point

func area(shape:Shape)-> Double{
    switch shape {
    case let .Square(side):
        return side*side
    case let .Rectangle(width,height):
        return width * height
    case let .Circle(_,_,r):  //下划线 忽略参数
        return M_PI*r*r
    case .Point:
        return 0
//        
//    default:
//        return 0
    }
}

area(square)
area(rectangel)
area(circle)
area(point)

四.可选型和枚举类型的 渊源

var age:Int? = 17

print(age)

/**
 *  enum Optional<Wrapped> : _Reflectable, NilLiteralConvertible
 点击查看发现 Optional 就是 enum 枚举类型 中的关联数据,包含 
enum Option{
       Some(AnyObject)
       None
}
 Some 是Optional 一个可选性
 */
var website:Optional<String> = Optional.Some("www.baidu.com")
// 
website = "www.baidu.com"

//website = nil
//website = .None

switch website{
case .None:
    print("No website")
case let .Some(website):
    print("The website is \(website)")
}



/// 解包 来源于  上面swich 的赋值 简写
if let website = website{
    print("The website is \(website)")
}

五. 枚举关联数据类型 使用递归的变态实例

/**
 递归声明
 添加关键字  indirect
 
 */

indirect enum ArithmeticExpression {
    case Number(Int)
    case Addition(ArithmeticExpression,ArithmeticExpression)
    case Multiplication(ArithmeticExpression,ArithmeticExpression)
}


let five  = ArithmeticExpression.Number(5)
let four  = ArithmeticExpression.Number(4)
let two   = ArithmeticExpression.Number(2)
let sum   = ArithmeticExpression.Addition(five, four)
let product = ArithmeticExpression.Multiplication(sum, two)


func evaluate(expression:ArithmeticExpression) -> Int {
    switch expression {
    case let .Number(value):
        return value
    case let .Addition(left,right):
        return evaluate(left)+evaluate(right)
    case let .Multiplication(left,right):
        return evaluate(left)*evaluate(right)
        
    }
}


evaluate(product)