有没有办法在Swift中为ErrorType值指定错误代码？

Question

In my app I am using a custom error type ProgrammerError with three error values .Messiness , .Procrastination and .Arrogance (these are just examples). Later in the code I need to cast the errors to NSError . The NSError objects have code properties starting from 0 following the order or error values I declared: 0, 1, 2 etc.

enum ProgrammerError: ErrorType {
  case Messiness
  case Procrastination
  case Arrogance
}

(ProgrammerError.Messiness as NSError).code // 0
(ProgrammerError.Procrastination as NSError).code // 1
(ProgrammerError.Arrogance as NSError).code // 2

My question is : Is there a way to set different error codes for the enumeration values? For example, can I set Messiness to have code value of 100 instead of 0?

Answer 1

You can implement var _code: Int { get } property.

enum ProgrammerError: ErrorType {
    case Messiness
    case Procrastination
    case Arrogance

    var _code: Int {
        switch self {
        case .Messiness:
            return 100
        case .Procrastination:
            return 101
        case .Arrogance:
            return 102
        }
    }
}

(ProgrammerError.Messiness as NSError).code // 100
(ProgrammerError.Procrastination as NSError).code // 101
(ProgrammerError.Arrogance as NSError).code // 102

You can also implement var _domain: String { get } if you need.

But I must warn you, these methods are undocumented so they might stop working in future.

Answer 2

Or, you may try explicit conversion.

extension FileActionError {
    func getCode() -> Int {
        switch self {
        case .BadFileNodeIndex:     return 1
        case .BadFileNodePath:      return 2
        }
    }
    func toNSError() -> NSError {
        return NSError(domain: "", code: getCode(), userInfo: [NSLocalizedDescriptionKey: "\(self)"])
    }
}

Might not what you expected.