Swift---8.枚举

• 枚举
  • 写法(以enum关键字开头,后跟名称,{}内是枚举内容,每一个枚举值使用关键字case标志)

  enum Week {
      case Monday
      case Tuesday
      case Wednesday
      case Thursday
      case Friday
      case Saturday
      case Sunday
  }
  enum anotherWeek {
      case Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,Sunday
  }
  

  • Swift中,枚举会定义一个全新的类型

  //简单写法
  enum Week {
      case Monday
      case Tuesday
      case Wednesday
      case Thursday
      case Friday
      case Saturday
      case Sunday
  }
  //合并写法
  enum anotherWeek {
      case Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,Sunday
  }
  //定义枚举变量
  var first = Week.Monday
  var second = anotherWeek.Saturday
  //枚举值匹配,匹配时,我们必须明确枚举内的每个值都不会遗漏
  switch first {
  case .Monday,.Tuesday,.Wednesday,.Thursday,.Friday:
      print("工作日")
  case .Saturday,.Sunday:
      print("休息")
  }
  //当不需要详尽匹配时,我们也可以使用"default"来标识不需要明确处理的成员
  switch second {
  case .Monday,.Tuesday,.Wednesday,.Thursday,.Friday:
      print("工作日")
  default:
      print("休息")
  }
  

  • 值关联(我们可以在枚举中提供相关类型的关联值,在使用switch进行匹配时,我们可以用let或者var来提取每个变量,当整个分支语句的所有变量都需要提取时,我们可以把let或者var写在成员变量前)

  enum Request {
      case result(Int,String)
  }
  var success = Request.result(200, "Success")
  switch success {
  case .result(let code,let message):
      print("the resultCode is \(code) request \(message)")
  }
  switch success {
  case let .result(code,message):
      print("the resultCode is \(code) request \(message)")
  }
  

  • 原始值:
    在Swift中,定义枚举时,如果我们给枚举设置类型,那么枚举的每个成员都会相应的附上一个对应类型的原始值,此时我们可以根据这个原始值来生成枚举中的一个变量.
    以下面代码为例,Week(rawValue:str)会返回一个Week?的类型,所以我们对他进行枚举时,必须确保其不为nil

  enum Week:String {
      case Monday
      case Tuesday
      case Wednesday
      case Thursday
      case Friday
      case Saturday
      case Sunday
  }
  var str = "Monday"
  if var strOfWeek = Week(rawValue: str) {
      switch strOfWeek {
      case .Monday,.Tuesday,.Wednesday,.Thursday,.Friday:
          print("工作日")
      default:
          print("休息")
      }
  }
  

  • 递归枚举(在成员变量前,加indirect关键字,表明该成员可以被递归)

  enum ArithmeticExpression {
      case number(Int)
      indirect case addition(ArithmeticExpression, ArithmeticExpression)
      indirect case multiplication(ArithmeticExpression, ArithmeticExpression)
  }
  let value1 = ArithmeticExpression.number(4)
  let value2 = ArithmeticExpression.number(5)
  let sum = ArithmeticExpression.addition(value1, value2)
  let product = ArithmeticExpression.multiplication(sum, ArithmeticExpression.number(2))
  func evalute(_ expression:ArithmeticExpression) ->Int {
      switch expression {
      case let .number(a):
          return a
      case let .addition(value1, value2):
          return evalute(value1) + evalute(value2)
      case let .multiplication(value1,value2):
          return evalute(value1) * evalute(value2)
      }
  }
  evalute(product)