枚举的定义和使用

import UIKit

// 枚举的定义和使用
enum CompassPoint {
    case north
    case south
    case east
    case west
}

enum Planet {
    case mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
}

var directionToHead = CompassPoint.west

directionToHead = .east
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")
}

let somePlanet = Planet.earth
switch somePlanet {
case .earth:
    print("Mostly harmless")
default:
    print("Not a safe place for humans")
}

console log 如下

枚举的定义和使用.png

关联值

// 关联值
enum Barcode {
    case upc(Int, Int, Int, Int)
    case qrCode(String)
}

var productBarcode = Barcode.upc(1992, 8, 5, 520)
productBarcode = Barcode.qrCode("ILoveU,Y")

switch productBarcode {
case .upc(let year, let month, let day, let check):
    print("UPC: \(year)年\(month)月\(day)日\(check)")
case .qrCode(let productCode):
    print("QR code:\(productCode)")
}

console log 如下

关联值.png

枚举的初始值

// 枚举的初始值
enum ASCIIControlCharacter: Character {
    case tab = "\t"
    case lineFeed = "\n"
    case carriageReturn = "\r"
}

enum AnotherPlanet: Int {
    case mercury = 1, venus, earth, mars, jupiter, saturn, uranus, neptune
}

let earthsOrder = AnotherPlanet.earth.rawValue
print("Earth order is \(earthsOrder)")

console log 如下

枚举的初始值.png

初始值初始化枚举值

// 初始值初始化枚举值
let positionToFind = 5
if let somePlanet = AnotherPlanet(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)")
}

console log 如下

初始值初始化枚举值.png

递归枚举

// 递归枚举
enum ArithmeticExpression {
    case number(Int)
    indirect case addition(ArithmeticExpression, ArithmeticExpression)
    indirect case multiplication(ArithmeticExpression, ArithmeticExpression)
}

let four = ArithmeticExpression.number(4)
let five = ArithmeticExpression.number(5)
let sum = ArithmeticExpression.addition(four, five)
let product = ArithmeticExpression.multiplication(sum, ArithmeticExpression.number(2))

func evaluate(expression: ArithmeticExpression) -> Int {
    switch expression {
    case let .number(value):
        return value
    case let .addition(left, right):
        return evaluate(left) + evaluate(right)
    case let .multiplication(left, right):
        return evaluate(left) * evaluate(right)
    }
}

print(evaluate(sum))
print(evaluate(product))

console log 如下

递归枚举.png