《浅入浅出Swift》Enumerations 枚举

####Enumerations

        //首字母大写
        enum SomeEnumeration{
            
        }
        /*        enum CompassPoint{            case North            case South            case East            case West        }        */
        enum CompassPoint{
            case North
            case South
            case East
            case West
        }
        */
        //or
        enum CompassPoint{
            case North,South,East,West
        }
        enum Planet {
            case Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
        }
        
        //既然是类型,就用enum定义变量
        var directionToHead = CompassPoint.West
        //初始化了CompassPoint后，就不再需要再写枚举的类型了
        directionToHead = .East
        
        //switch中也是类似
        switch directionToHead{
        case .North:println("Lots of planets have a north")
        case .South:println("Watch out for penguins")
        case .East:println("Where the sun rises")
        case .West:println("Where the skies are blue")
        //prints "Where the sun rises"
        }
        
        let somePlanet = Planet.Earth
        switch somePlanet{
        case .Earth:println("Mostly harmless")
        default:println("Not a safe place for humans")
        }
        
        //关联值，Associated Values
        //Barcod不存储任何东西，仅仅定义了类型，需要再定义变量
        enum Barcode{
            case UPCA(Int,Int,Int,Int)
            case QRCode(String)
        }
        var productBarcode = Barcode.UPCA(8, 85909, 51226, 3)
        productBarcode = .QRCode("ABCDEFGHIJKLMNOP")
        
//        switch productBarcode{
//            case .UPCA(let numberSystem, let manufacturer, let product, let check):
//            println("UPC-A: \(numberSystem),\(manufacturer),\(product),\(check)")
//            case .QRCode(let productCde):
//            println("QR code:\(productBarcode)")
//        }
        //值是var or let 可以提前
        switch productBarcode{
        case let .UPCA(numberSystem, manufacturer, product, check):
            println("UPC-A: \(numberSystem),\(manufacturer),\(product),\(check)")
        case let .QRCode(productCde):
            println("QR code:\(productBarcode)")
        }
        
        
        //可以为enum定义值，Raw Values
        enum ASCIIControlCharacter :Character{
            case Tab = "\t", LineFeed = "\n", CarriageReturn = "\r"
        }
        enum NewPlanet:Int{
            case Mercury = 1, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
        }
        //toRaw 取到枚举的值
        let earthsOrder = NewPlanet.Earth.toRaw()
        println("earthsOrder 取值 ＝ \(earthsOrder)")
        //fromRaw 通过值取到NewPlanet成员
        let possiblePlanet = NewPlanet.fromRaw(7)
        println("possiblePlanet 取枚举 = \(possiblePlanet)")
        
        var whichPlanet: NewPlanet? = NewPlanet.fromRaw(10000)
        println("whichPlanet = \(whichPlanet)")

Reference

• The Swift Programming Language