如果我有一个带有原始Integer值的枚举:
Integer
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?
city
Melbourne
类似的东西(此代码将不起作用):
println("Your city is \(city.magicFunction)") > Your city is Melbourne
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:
print(_:)
String
init(_:)
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(_:)
String(reflecting:)
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。)
\(self)
description
debugDescription
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:
init(reflecting:)
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) }
有关此更改的信息, 请参见发行说明。