Swift 如何枚举字符串类型的枚举

发布于03月31日

enum Suit: String {
    case spades = "♠"
    case hearts = "♥"
    case diamonds = "♦"
    case clubs = "♣"
}

例如，我如何做以下事情:

for suit in Suit {
    // do something with suit
    print(suit.rawValue)
}

结果示例:

♠
♥
♦
♣

推荐答案

Swift 4.2+

从Swift 4.2开始(使用Xcode 10)，只需将协议一致性添加到CaseIterable即可从allCases中获益.要添加此协议一致性，只需在某个地方编写:

extension Suit: CaseIterable {}

如果枚举是您自己的，您可以直接在声明中指定一致性:

enum Suit: String, CaseIterable { case spades = "♠"; case hearts = "♥"; case diamonds = "♦"; case clubs = "♣" }

然后，以下代码将打印所有可能的值:

Suit.allCases.forEach {
    print($0.rawValue)
}

与早期Swift版本(3.x和4.x)的兼容性

如果你需要支持Swift 3.在x或4.0中，您可以通过添加以下代码来模拟Swift 4.2的实现:

#if !swift(>=4.2)
public protocol CaseIterable {
    associatedtype AllCases: Collection where AllCases.Element == Self
    static var allCases: AllCases { get }
}
extension CaseIterable where Self: Hashable {
    static var allCases: [Self] {
        return [Self](AnySequence { () -> AnyIterator<Self> in
            var raw = 0
            var first: Self?
            return AnyIterator {
                let current = withUnsafeBytes(of: &raw) { $0.load(as: Self.self) }
                if raw == 0 {
                    first = current
                } else if current == first {
                    return nil
                }
                raw += 1
                return current
            }
        })
    }
}
#endif