swift2 枚举类型

枚举语法

enum Compasspoint {
    case north
    case South
    case East
    case West
}
var directionToHead = Compasspoint.West
directionToHead = .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.West

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")
}
// 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),\(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.Uranus
let positionToFind = 9
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)")
}
// 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。