要在一個類型中嵌套另一個類型秀仲，將嵌套類型的定義寫在其外部類型的{}
內(nèi)，而且可以根據(jù)需要定義多級嵌套神僵。在外部引用嵌套類型時，在嵌套類型的類型名前加上其外部類型的類型名作為前綴保礼。
struct BlackjackCard {
// 嵌套的 Suit 枚舉
enum Suit: Character {
case Spades = "?", Hearts = "?", Diamonds = "?", Clubs = "?"
}
// 嵌套的 Rank 枚舉
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 的屬性和方法
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)")
// 打印 “theAceOfSpades: suit is ?, value is 1 or 11”
let heartsSymbol = BlackjackCard.Suit.Hearts.rawValue
// 紅心符號為 “?”
- 一般來說，類相對較大侯勉，結(jié)構(gòu)體或者枚舉相對較小铝阐，所以在適當(dāng)?shù)臅r候址貌，在類中嵌套枚舉或者結(jié)構(gòu)體作為數(shù)據(jù)結(jié)構(gòu)
- 將一些零散的小定義放到一個大的名字空間里徘键，封裝一下
- 不是必要的情況，這種方式不要用吹害，影響可讀性
