swift 2 : Error handling: throw: How to pass an object with an error?

Question

Swift2抛错时如何传递userInfo引用对象？

像这样的东西会很好:

guard let refIDString = memberXMLElement.attributes["ref"] else {
     throw OSMVectorMapDescriptionError.ElementDoesntContainRequiredAttributes(userInfo:memberXMLElement)
}

然后:

catch OSMVectorMapDescriptionError.ElementDoesntContainRequiredAttributes {
  (userInfo:AnyObject) in
      //do stuff                 
 }

但是错误是枚举，我们确实可以像这里那样指定，但是如何捕捉呢？

public enum OSMVectorMapDescriptionError:ErrorType {
    case ElementDoesntContainRequiredAttributes(userInfo:AnyObject)
}

Answer 1

假设你不需要someLevel，你可以定义

public enum OSMVectorMapDescriptionError:ErrorType {
   case ElementDoesntContainRequiredAttributes(userInfo: ...)
}

保持警惕

guard let refIDString = memberXMLElement.attributes["ref"] else {
    throw OSMVectorMapDescriptionError.
              ElementDoesntContainRequiredAttributes(userInfo:memberXMLElement)
}

和

catch OSMVectorMapDescriptionError.
          ElementDoesntContainRequiredAttributes(let userInfo) {
  //do stuff using userInfo              
}