Swift开发基础04-枚举
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)
有时会将枚举的成员值跟其他类型的关联存储在一起,会非常有用
enum Score { case points(Int) case grade(Character) } var score = Score.points(96) score = .grade("A") switch score { case let .points(i): print(i, "points") case let .grade(i): print("grade", i) } // 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) } // 必要时let也可以改为var
原始值(Raw Values)
枚举成员可以使用相同类型的默认值预先关联,这个默认值叫做:原始值
enum PokerSuit : Character { case spade = "♠" case heart = "♥" case diamond = "♦" case club = "♣" } var suit = PokerSuit.spade print(suit) // spade print(suit.rawValue) // ♠ print(PokerSuit.club.rawValue) // ♣
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
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 (indirect)
indirect enum ArithExpr { case number(Int) case sum(ArithExpr, ArithExpr) case difference(ArithExpr, ArithExpr) } 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)
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)
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<Password>.stride // 40, 分配占用的空间大小 MemoryLayout<Password>.size // 33, 实际用到的空间大小 MemoryLayout<Password>.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
窥探枚举的内存
1、枚举有2个case及以上的情况
enum TestEnum { case test1(Int, Int, Int) case test2(Int, Int) case test3(Int) case test4(Bool) case test5 }
MemoryLayout<TestEnum>.stride // 32, 分配占用的空间大小
MemoryLayout<TestEnum>.size // 25, 实际用到的空间大小
MemoryLayout<TestEnum>.alignment // 8, 对齐参数
通过观察枚举变量e的内存布局:
test1
// 1个字节存储成员值 // N个字节存储关联值(N取占用内存最大的关联值),任何一个case的关联值都共用这N个字节 // 共用体 // 小端:高高低低 // 01 00 00 00 00 00 00 00 // 02 00 00 00 00 00 00 00 // 03 00 00 00 00 00 00 00 // 00 // 00 00 00 00 00 00 00 var e = TestEnum.test1(1, 2, 3)
test2
// 04 00 00 00 00 00 00 00 // 05 00 00 00 00 00 00 00 // 00 00 00 00 00 00 00 00 // 01 // 00 00 00 00 00 00 00 e = .test2(4, 5)
test3
// 06 00 00 00 00 00 00 00 // 00 00 00 00 00 00 00 00 // 00 00 00 00 00 00 00 00 // 02 // 00 00 00 00 00 00 00 e = .test3(6)
test4
// 01 00 00 00 00 00 00 00 // 00 00 00 00 00 00 00 00 // 00 00 00 00 00 00 00 00 // 03 // 00 00 00 00 00 00 00 e = .test4(true)
test5
// 00 00 00 00 00 00 00 00 // 00 00 00 00 00 00 00 00 // 00 00 00 00 00 00 00 00 // 04 // 00 00 00 00 00 00 00 e = .test5
2、枚举只有1个case的情况(其实一个case也多大意义了)
enum TestEnum { case test1(Int, Int, Int) } var e = TestEnum.test1(10, 20, 30) MemoryLayout.stride(ofValue: e) // 24, 分配占用的空间大小 MemoryLayout.size(ofValue: e) // 24, 实际用到的空间大小 MemoryLayout.alignment(ofValue: e) // 8, 对齐参数
test1
// 0A 00 00 00 00 00 00 00 // 14 00 00 00 00 00 00 00 // 1E 00 00 00 00 00 00 00 var e = TestEnum.test1(10, 20, 30)
这种情况就不需要存储成员值了,直接开辟24个字节存关联值
将来的你会感谢今天如此努力的你!
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