Nested Types

为了表示更复杂的结构，swift中类、结构体和枚举可以使用内嵌类型

在结构体中嵌套枚举的复杂实例

  //Nested Types in Action
  struct BlackJackCard {
  
  //nested Suit enumeration
  enum Suit:Character {
      case spades = "♠️", hearts = "♥️", diamonds = "◇", clubs = "♣️"
  }
  
  //nested Rank enumeration
  enum Rank: Int {
      case two = 2, three, four, five, six, seven, eight, nine, ten
      case jack, queen, king, ace
      struct Values {
          let first:Int, second: Int?
      }
      var values:Values {
          switch self {
          case .ace:
              return Values(first: 1, second: 11)
          case .jack, .queen, .king:
              return Values(first: 10, second: nil)
          default:
              return Values(first: self.rawValue, second: nil)
          }
      }
      
  }
  
  //BlackJackCard properities and methods
  let rank: Rank, suit:Suit
  var description: String {
      var output = "suit is \(suit.rawValue)"
      output += "value is \(rank.values.first)"
      if let second = rank.values.second {
          output += "or \(second)"
      }
      return output
  }
  
}

let theAceOfSpades = BlackJackCard(rank: .ace, suit: .spades)
print("theAceOfSpades: \(theAceOfSpades.description)")

可以直接只用类型.类型访问

let heartSymbol = BlackJackCard.Suit.hearts.rawValue