Swift枚举

枚举的基本用法

enum Direction {
    case north
    case south
    case east
    case west 
}

enum Direction {
    case north, south, east, west
}

var dir = Direction.west
dir = Direction.east
dir = .north
print(dir) // north

switch dir {
case .north:
    print("north")
case .south:
    print("south")
case .east:
    print("east")
case .west:
    print("west")
}

---

关联值(Associated Values)

有时将枚举的成员值跟其他类型的值关联存储在一起，会非常有用

enum Score {
    case points(Int)
    case grade(Character)
}

var score = Score.points(96)
score = .grade("A")

enum Date {
    case digit(year: Int, month: Int, day: Int)
    case string(String)
}

var date = Date.digit(year: 2011, month: 9, day: 10)
date = .string("2011-09-10")

switch date {
case .digit(let year, let month, let day):
    print(year, month, day)
case let .string(value):
    print(value)
}

switch score {
case let .points(i):
    print(i, "points")
case let .grade(i):
    print("grade", i)
} // grade A

必要时let也可以改为var

---

关联值举例

enum Password {
    case number(Int, Int, Int, Int)
    case gesture(String)
}

var pwd = Password.number(3, 5, 7, 8)
pwd = .gesture("12369")

switch pwd {
case let .number(n1, n2, n3, n4):
    print("number is ", n1, n2, n3, n4)
case let .gesture(str):
    print("gesture is", str)
}

---

原始值(Raw Values)

枚举成员可以使用相同类型的默认值预先对应，这个默认值叫做:原始值

enum PokerSuit : Character {
    case spade = "♠"
    case heart = "♥"
    case diamond = "♦"
    case club = "♣"
}
enum Grade : String {
    case perfect = "A"
    case great = "B"
    case good = "C"
    case bad = "D"
}
print(Grade.perfect.rawValue) // A
print(Grade.great.rawValue) // B
print(Grade.good.rawValue) // C
print(Grade.bad.rawValue) // D
var suit = PokerSuit.spade print(suit) // spade print(suit.rawValue) // ♠ print(PokerSuit.club.rawValue) // ♣

注意:原始值不占用枚举变量的内存

---

隐式原始值(Implicitly Assigned Raw Values)

如果枚举的原始值类型是Int、String，Swift会自动分配原始值

enum Direction : String {
    case north = "north"
    case south = "south"
    case east = "east"
    case west = "west"
}
// 等价于
enum Direction : String {
    case north, south, east, west
}
print(Direction.north) // north
print(Direction.north.rawValue) // north

enum Season : Int {
    case spring, summer, autumn, winter
}
print(Season.spring.rawValue) // 0
print(Season.summer.rawValue) // 1
print(Season.autumn.rawValue) // 2
print(Season.winter.rawValue) // 3

enum Season : Int {
    case spring = 1, summer, autumn = 4, winter
}
print(Season.spring.rawValue) // 1
print(Season.summer.rawValue) // 2
print(Season.autumn.rawValue) // 4
print(Season.winter.rawValue) // 5

---

递归枚举(Recursive Enumeration)

indirect enum ArithExpr {
    case number(Int)
    case sum(ArithExpr, ArithExpr)
    case difference(ArithExpr, ArithExpr)
}
func calculate(_ expr: ArithExpr) -> Int { switch expr {
    case let .number(value):
        return value
    case let .sum(left, right):
        return calculate(left) + calculate(right)
    case let .difference(left, right):
        return calculate(left) - calculate(right)
} }
calculate(difference)

enum ArithExpr {
    case number(Int)
    indirect case sum(ArithExpr, ArithExpr) indirect case difference(ArithExpr, ArithExpr)
}
let five = ArithExpr.number(5)
let four = ArithExpr.number(4)
let two = ArithExpr.number(2)
let sum = ArithExpr.sum(five, four)
let difference = ArithExpr.difference(sum, two)

---

MemoryLayout

可以使用MemoryLayout获取数据类型占用的内存大小

enum Password {
    case number(Int, Int, Int, Int)
    case other
}
MemoryLayout.stride // 40, 分配占用的空间大小 MemoryLayout.size // 33, 实际用到的空间大小 MemoryLayout.alignment // 8, 对齐参数
var pwd = Password.number(9, 8, 6, 4)
pwd = .other

MemoryLayout.stride(ofValue: pwd) // 40
MemoryLayout.size(ofValue: pwd) // 33
MemoryLayout.alignment(ofValue: pwd) // 8