swift2 枚举类型

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枚举语法

enum CompassPoint {    case North    case South    case East    case West}var directionToHead = CompassPoint.WestdirectionToHead = .South

directionToHead的类型被推断当它被CompassPoint的一个可能值初始化。

一旦directionToHead被声明为一个CompassPoint，你可以使用更短的点（.）语法将其设置为另一个CompassPoint的值.

匹配枚举值

enum CompassPoint {    case North    case South    case East    case West}var directionToHead = CompassPoint.WestdirectionToHead = .Southswitch 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")}// 输出 "Watch out for penguins”

相关值

enum Barcode {    case UPCA(Int, Int, Int)    case QRCode(String)}var productBarcode = Barcode.UPCA(8, 85909_51226, 3)productBarcode = .QRCode("ABCDEFGHIJKLMNOP")switch productBarcode {case .UPCA(let numberSystem, let identifier, let check):    print("UPC-A with value of \(numberSystem), \(identifier), \(check).")case .QRCode(let productCode):    print("QR code with value of \(productCode).")}// 输出 "QR code with value of ABCDEFGHIJKLMNOP.”

如果一个枚举成员的所有相关值被提取为常量，或者它们全部被提取为变量，为了简洁，你可以只放置一个var或者let标注在成员名称前：

switch productBarcode {case let .UPCA(numberSystem, identifier, check):    print("UPC-A with value of \(numberSystem), \(identifier), \(check).")case let .QRCode(productCode):    print("QR code with value of \(productCode).")}// 输出 "QR code with value of ABCDEFGHIJKLMNOP."

原始值

enum Planet: Int {    case Mercury = 1, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune}let earthsOrder = Planet.Earth.rawValue// earthsOrder is 3

枚举类型可以用原始值进行预先填充，上述枚举的原始值类型为int

同时可以通过rawValue访问原始值，可以通过原始值创建枚举

let possiblePlanet = Planet(rawValue: 7)// possiblePlanet is of type Planet? and equals Planet.Uranuslet positionToFind = 9if 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)")}// 输出 "There isn't a planet at position 9

这个范例使用可选绑定（optional binding），通过原始值9试图访问一个行星。

if let somePlanet = Planet(rawValue: 9)语句获得一个可选Planet，如果可选Planet可以被获得，把somePlanet设置成该可选Planet的内容。

在这个范例中，无法检索到位置为9的行星，所以else分支被执行。

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