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