如何在Swift中获取枚举值的名称？

  • Z时代
  • 2024-01-10
  • 分类：问答

如果我有一个带有原始Integer值的枚举：

enum City: Int {
  case Melbourne = 1, Chelyabinsk, Bursa
}
let city = City.Melbourne

如何将city值转换为字符串Melbourne？语言中是否可用这种类型名称自省？

类似的东西（此代码将不起作用）：

println("Your city is \(city.magicFunction)")
> Your city is Melbourne

回答：

从Xcode 7 beta

5（Swift版本2）开始，您现在可以默认使用来打印类型名称和枚举大小写print(_:)，或者String使用String的init(_:)初始值设定项或字符串插值语法转换为。因此，对于您的示例：

enum City: Int {
    case Melbourne = 1, Chelyabinsk, Bursa
}
let city = City.Melbourne
print(city)
// prints "Melbourne"
let cityName = "\(city)"   // or `let cityName = String(city)`
// cityName contains "Melbourne"

因此，不再需要定义和维护一个方便函数，该函数在每种情况下都可以打开以返回字符串文字。此外，即使未指定原始值类型，此方法也可自动用于任何枚举。

debugPrint(_:)＆String(reflecting:)可以用作标准名称：

debugPrint(city)
// prints "App.City.Melbourne" (or similar, depending on the full scope)
let cityDebugName = String(reflecting: city)
// cityDebugName contains "App.City.Melbourne"

请注意，您可以自定义在每种情况下打印的内容：

extension City: CustomStringConvertible {
    var description: String {
        return "City \(rawValue)"
    }
}
print(city)
// prints "City 1"
extension City: CustomDebugStringConvertible {
    var debugDescription: String {
        return "City (rawValue: \(rawValue))"
    }
}
debugPrint(city)
// prints "City (rawValue: 1)"

（我还没有找到一种方法来调用此“默认”值，例如，在不诉诸switch语句的情况下打印“城市是墨尔本”。\(self)在description/

的实现中使用debugDescription会导致无限递归。）

上面String的init(_:)＆init(reflecting:)初始值设定项中的注释确切描述了打印的内容，具体取决于所反映的类型符合：

extension String {
    /// Initialize `self` with the textual representation of `instance`.
    ///
    /// * If `T` conforms to `Streamable`, the result is obtained by
    ///   calling `instance.writeTo(s)` on an empty string s.
    /// * Otherwise, if `T` conforms to `CustomStringConvertible`, the
    ///   result is `instance`'s `description`
    /// * Otherwise, if `T` conforms to `CustomDebugStringConvertible`,
    ///   the result is `instance`'s `debugDescription`
    /// * Otherwise, an unspecified result is supplied automatically by
    ///   the Swift standard library.
    ///
    /// - SeeAlso: `String.init<T>(reflecting: T)`
    public init<T>(_ instance: T)
    /// Initialize `self` with a detailed textual representation of
    /// `subject`, suitable for debugging.
    ///
    /// * If `T` conforms to `CustomDebugStringConvertible`, the result
    ///   is `subject`'s `debugDescription`.
    ///
    /// * Otherwise, if `T` conforms to `CustomStringConvertible`, the result
    ///   is `subject`'s `description`.
    ///
    /// * Otherwise, if `T` conforms to `Streamable`, the result is
    ///   obtained by calling `subject.writeTo(s)` on an empty string s.
    ///
    /// * Otherwise, an unspecified result is supplied automatically by
    ///   the Swift standard library.
    ///
    /// - SeeAlso: `String.init<T>(T)`
    public init<T>(reflecting subject: T)
}

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