--- /dev/null
+//: [Previous](@previous)
+
+import UIKit
+
+enum CompassPoint {
+ case North
+ case East
+ case South
+ case West
+}
+
+var directionToHead = CompassPoint.North
+directionToHead = .East
+
+switch directionToHead {
+ case .North: print("Losts of Plantes Have a North")
+ case .East : print("Where the Sun Rises")
+ case .South: print("Watch Out for Penguins")
+ case .West : print("Where the Skies are Blue")
+}
+
+
+// Associated Values
+printLine("Enumeration Associated Values")
+enum BarCode {
+ case UPCA(Int, Int, Int, Int)
+ case QRCode(String)
+}
+
+var productBarCode = BarCode.UPCA(8, 88488, 66366, 2)
+productBarCode = .QRCode("QRCode-123456")
+
+switch productBarCode {
+case let .UPCA(numberSystem, manufacturer, product, check) :
+ print("UPC-A: \(numberSystem), \(manufacturer), \(product), \(check)")
+case let .QRCode(productCode) :
+ print("QR Code: \(productBarCode)")
+}
+
+
+printLine("RawValues")
+// Raw Values
+enum ASCIIControlCharacter: Character {
+ case Tab = "\t"
+ case LineFeed = "\n"
+ case CarriageReturn = "\r"
+}
+
+// Implicitly Assigned Raw Values
+// 整型从0开始自增1，每个项的rawValue不能相同
+enum Planet: Int {
+ case Mercury
+ case Venus
+ case Earth
+ case Mars
+ case Jupiter
+ case Saturn
+ case Uranus
+ case Netpune
+}
+
+print(Planet.Mercury, Planet.Mercury.rawValue)
+print(Planet.Mars, Planet.Mars.rawValue)
+print(Planet(rawValue: 5)!, Planet(rawValue: 5)!.rawValue)
+
+
+// String型，每项默认为枚举项的字符串值
+enum CompassPointString: String {
+ case North
+ case East
+ case Sourth
+ case West
+}
+
+
+print(CompassPointString.North, CompassPointString.North.rawValue)
+print(CompassPointString.East, CompassPointString.East.rawValue)
+print(CompassPointString.Sourth,CompassPointString.Sourth.rawValue)
+print(CompassPointString.West, CompassPointString.West.rawValue)
+
+
+printLine("Resursive Enumerations")
+// 不能忘记 indirect
+indirect enum Exp {
+ case Number(Int)
+ case Add(Exp, Exp) // indirect 也可以放在case语句之前
+ case Mul(Exp, Exp)
+}
+
+
+let exp = Exp.Mul(Exp.Add(Exp.Number(2), Exp.Number(5)), Exp.Number(7))
+
+func evaluateExp(exp: Exp) -> Int {
+ switch exp {
+ case let .Number(n):
+ return n
+ case let .Add(a, b) :
+ return evaluateExp(a) + evaluateExp(b)
+ case let .Mul(a, b):
+ return evaluateExp(a) * evaluateExp(b)
+ }
+}
+
+print(evaluateExp(exp))