如何在Swift中获取枚举值的名称? [英] How to get the name of enumeration value in Swift?

问题描述

如果我使用原始的 Integer 值进行枚举:

If I have an enumeration with raw Integer values:

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

let city = City.Melbourne

如何将 city 值转换为字符串 Melbourne ?这种语言类型的自省可以使用吗?

How can I convert a city value to a string Melbourne? Is this kind of a type name introspection available in the language?

类似的东西(此代码将不起作用):

Something like (this code will not work):

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

推荐答案

从Xcode 7 beta 5(Swift版本2)开始，您现在可以使用 print(_ :)默认打印类型名称和枚举大小写，或使用 String 的 init(_:)初始值设定项或字符串插值语法转换为 String .因此，对于您的示例:

As of Xcode 7 beta 5 (Swift version 2) you can now print type names and enum cases by default using print(_:), or convert to String using String's init(_:) initializer or string interpolation syntax. So for your example:

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&维护一个便利函数，该函数在每种情况下均会打开以返回字符串文字.此外，即使未指定原始值类型，此方法也可以自动用于任何枚举.

So there is no longer a need to define & maintain a convenience function that switches on each case to return a string literal. In addition, this works automatically for any enum, even if no raw-value type is specified.

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

debugPrint(_:) & String(reflecting:) can be used for a fully-qualified name:

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，您可以自定义以下每种情况下的打印内容:

Note that you can customise what is printed in each of these scenarios:

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，在不求助于switch语句的情况下，打印城市是墨尔本".使用 \(self)在 description / debugDescription 的实现中会导致无限递归.)

(I haven't found a way to call into this "default" value, for example, to print "The city is Melbourne" without resorting back to a switch statement. Using \(self) in the implementation of description/debugDescription causes an infinite recursion.)

String 的 init(_:)&上方的注释 init(reflecting:)初始值设定项准确描述要打印的内容，具体取决于所反映的类型符合以下条件:

The comments above String's init(_:) & init(reflecting:) initializers describe exactly what is printed, depending on what the reflected type conforms to:

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)
}

请参见发行说明以获取有关此更改的信息.

See the release notes for info about this change.

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