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 = 0
        while let item = Self(rawValue: value)
        {
            result.append(item)
            value += 1
        }
        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 { $0.permanentID == id }.flatMap { self.init(rawValue: $0) }
    }
}