代码1:
protocol PickableEnum

{

    var displayName: String { get }

    var permanentID: String { get }

    static var allValues: [Self] { get }

    static func fromPermanentID(id: String) -> Self?

}

//下面的扩展表面了这个协议的实例必须实现了RawRepresentable协议,并且字面值必须是Int类型

extension PickableEnum where Self: RawRepresentable, Self.RawValue == Int

{

    var displayName: String

    {

        return Localised("\(self.dynamicType).\(self)")

    }

    var permanentID: String

    {

        return String(self)

    }

    static var allValues: [Self]

    {

        var result: [Self] = []

        var value =

        while let item = Self(rawValue: value)

        {

            result.append(item)

            value +=

        }

        return result

    }

    
　　//这个方法巧妙运用了函数式编程,通过id,在allValues数组中查询一个实现了此协议的对象

    static func fromPermanentID(id: String) -> Self?

    {

        return allValues.indexOf { $.permanentID == id }.flatMap { self.init(rawValue: $) }

    }

}