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), \(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.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。