空枚举
//空枚举
enum SomeEnumeration {
// enumeration definition goes here
}
枚举基本类型
//枚举基本类型
enum CompassPoint {
case north
case south
case east
case west
}
简写
//简写
enum Planet {
case mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
}
枚举语法
//枚举语法
func testEnumerationSyntax() {
//使用
var directionToHead = CompassPoint.west
//可不写 前面的枚举名
directionToHead = .east
print("\(directionToHead)")
/* print
east
*/
}
枚举匹配
//枚举匹配
func testMatchingEnumeration() {
var directionToHead = CompassPoint.south
//if匹配
if directionToHead == CompassPoint.south {
directionToHead = .east
}
//switch匹配
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")
default:
print("default")
}
/* print
Where the sun rises
*/
}
关联值
//关联值
func testAssociatedValues() {
//枚举可以和结构体类型的数据关联使用
enum Barcode {
case upca(Int, Int, Int, Int)
case qrCode(String)
}
// 初始化
var productBarcode = Barcode.upca(, , , )
productBarcode = .qrCode("ABCDEFGHIJKLMNOP")
//匹配
switch productBarcode {//有警告 要求是常数
case .upca(let numberSystem, let manufacturer, let product, let check):
print("UPC-A: \(numberSystem), \(manufacturer), \(product), \(check).")
case .qrCode(let productCode):
print("QR code: \(productCode).")
}
//可以不写let
switch productBarcode {
case let .upca(numberSystem, manufacturer, product, check):
print("UPC-A: \(numberSystem), \(manufacturer), \(product), \(check).")
case let .qrCode(productCode):
print("QR code: \(productCode).")
}
/* print
QR code: ABCDEFGHIJKLMNOP.
QR code: ABCDEFGHIJKLMNOP.
*/
}
原始值
//原始值
func testRawValues() {
enum ASCIIControlCharacter: Character {
case tab = "\t"
case lineFeed = "\n"
case carriageReturn = "\r"
}
//隐式分配原始值
enum Planet: Int {
case mercury = , venus, earth, mars, jupiter, saturn, uranus, neptune
}
//原始值为属性名转换
enum CompassPoint: String {
case North, South, East, West
}
print("\(Planet.earth.rawValue)")
print("\(CompassPoint.West.rawValue)")
// 通过原始值初始化
let possiblePlanet = Planet(rawValue: )
print("\(possiblePlanet)")
let positionToFind =
print("\(possiblePlanet)")
// 当原始值不匹配时，返回为nil
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)")
}
/* print
3
West
Optional(Swift_枚举.(testRawValues () -> ()).(Planet #1).uranus)
Optional(Swift_枚举.(testRawValues () -> ()).(Planet #1).uranus)
There isn't a planet at position 9
*/
}
枚举循环
//枚举循环
func testRecursiveEnumerations() {
//indirect循环关键字
// enum ArithmeticExpression {
// case Number(Int)
// indirect case Addition(ArithmeticExpression, ArithmeticExpression)
// indirect case Multiplication(ArithmeticExpression, ArithmeticExpression)
// }
// 可将indirect写到枚举前
indirect enum ArithmeticExpression {
case number(Int) // 值
case addition(ArithmeticExpression, ArithmeticExpression) // 加
case multiplication(ArithmeticExpression, ArithmeticExpression) // 乘
}
// 函数使用
func evaluate(_ expression: ArithmeticExpression) -> Int {
switch expression {
case .number(let value):
return value
case .addition(let left, let right):
return evaluate(left) + evaluate(right)
case .multiplication(let left, let right):
return evaluate(left) * evaluate(right)
}
}
// evaluate (5 + 4) * 2
let five = ArithmeticExpression.number()
let four = ArithmeticExpression.number()
let sum = ArithmeticExpression.addition(five, four)
let product = ArithmeticExpression.multiplication(sum, ArithmeticExpression.number())
print(evaluate(product))
/* print
18
*/
}
