Swift 3.0 学习笔记之枚举

enum CompassPoint{

    case north

    case south

    case east

    case west

} Swift中没有默认值 ，在C和OC中north=0，south=1，east=2，west=3

enum Planet{

       case mercury,venus,earth,mars,jupiter,saturn,uranus,neptune

}

var directionToHead=CompassPoint.west

directionToHead= .east

directionToHead= .south

switch directionToHead{

case  .north:

        print("Lots of planets have a north")

case  .south:

        print("Watch out for penguins") 

case  .east:

        print("Where the sun rises")

case  .west:

        print("Where the skies are blue")

}

// Prints "Watch out for penguins"

enum Barcode{

   case upc(Int,Int,Int,Int)//条形码

   case qrCode(String)//二维码

}

var productBarcode = Barcode.upc(8,85909,51226,3)

productBarcode= .qrCode("ABCDEFGHIJKLMNOP")

switch productBarcode{

case  .upc(let numberSystem,let manufacturer,let product,let check):

         print("UPC:\(numberSystem),\(manufacturer),\(product),\(check).")

case  .qrCode(let productCode):

         print("QR code:\(productCode).") 

}

// Prints "QR code: ABCDEFGHIJKLMNOP."

Raw Values // 初始值

enum  ASCIIControlCharacter:Character{

      case tab="\t"

      case lineFeed="\n"

      case carriageReturn="\r"

}

Implicitly Assigned Raw Values // 隐式分配的原始值

enum Planet:Int{

      case  mercury=1,venus,earth,mars,jupiter,saturn,uranus,neptune

} // venus=2,后面的一次递增

enum  CompassPoint:String{

        case  north,south,east,west

} // 默认初始值 north = "north" south = "south" 后面雷同

let positionToFind=11

if let somePlanet = Planet(rawValue:positionToFind)  {

          switch somePlanet{

                    case  .earth:

                         print("Mostly harmless")

                    default:

                         print("Not a safe place for humans")

          }

}else{

         print("There isn't a planet at position\(positionToFind)")

}

// Prints "There isn't a planet at position 11"

Recursive Enumerations  // 递归枚举

enum ArithmeticExpression{

       case number(Int)

       indirect case addition(ArithmeticExpression,ArithmeticExpression)

       indirect case multiplication(ArithmeticExpression,ArithmeticExpression)

}

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 sum=ArithmeticExpression.addition(five,four)

let product=ArithmeticExpression.multiplication(sum,ArithmeticExpression.number(2))

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)

           }

}

print(evaluate(product))               // Prints "18"