Swift从入门到精通第十六篇 - 嵌套类型 初识

嵌套类型（学习笔记）

环境Xcode 11.0 beta4 swift 5.1

• 嵌套类型的应用

  • 示例如下

    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 properties 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
        }
    }
    // BlackjackCard 内嵌套了两个枚举类型 Rank、Suit，Rank有一个更深的嵌套类型Values

    // BlackjackCard 有两个存储属性，没有显示的构造器， 由于Rank、Suit 都是其嵌套类型，所以可以推导出类型，下面可以直接（
    .ace .spades）
    let theAceOfSpades = BlackjackCard(rank: .ace, suit: .spades)
    print("theAceOfSpades: \(theAceOfSpades.description)")
    // Prints "theAceOfSpades: suit is ♠, value is 1 or 11"

• 嵌套类型的引用

  • 示例

    let heartSymbol = BlackjackCard.Suit.hearts.rawValue
    // heartSymbol is "♡"