1、枚举语法

• 每个成员值通过关键字 case 来定义。
• 成员名字必须以一个大写字母开头。
• 多个成员值可以出现在同一行上，用逗号隔开。

// 定义枚举
enum CompassPoint {
    case North
    case South
    case East
    case West
}
enum Planet {
    case Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
}

var directionToHead: CompassPoint = CompassPoint.West
directionToHead = .East		// 当已经推断出变量或常量的枚举类型后，访问时可以不写枚举名

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"

2、关联值（Associated Values）

// 定义了一个包含条形码和二维码的枚举
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 productCode):
    println("QR code: \(productCode).")
}
// prints "QR code: ABCDEFGHIJKLMNOP."

// 如果关联值中的数据类型一致，可将声明类型提取到成员值前
switch productBarcode {
case let .UPCA(numberSystem, manufacturer, product, check):
    println("UPC-A: \(numberSystem), \(manufacturer), \(product), \(check).")
case let .QRCode(productCode):
    println("QR code: \(productCode).")
}
// prints "QR code: ABCDEFGHIJKLMNOP."

3、原始值（Raw Values）

每个原始值在它的枚举声明中必须是唯一的。当整型值被用于原始值，如果其它枚举成员没有值时，它们会自动递增。

enum Planet: Int {
    case Mercury = 1, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
}

let earthsOrder = Planet.Earth.rawValue
let possiblePlanet = Planet(rawValue: 7)

let positionToFind = 9
if let somePlanet = Planet(rawValue: positionToFind) {
    switch somePlanet {
    case .Earth:
        println("Mostly harmless")
    default:
        println("Not a safe place for humans")
    }
} else {
    println("There isn't a planet at position \(positionToFind)")
}
// prints "There isn't a planet at position 9"

5、枚举是值类型

6、结语