.mapError() not working?

[pablorecio]

We are using Promissum in a legacy project that we are trying to upgrade to Swift 3, but I found some issues when doing so.

Say that I have something like:

class Api {
  // ... 
  fileprivate func requestJSON(_ path: Path) -> Promise<SuccessResponse<AnyObject>, ApiError> {
    let url = path.url(baseUrl)
    return manager
      .request(url)
      .responseJSONPromise()
      .mapError(self.errorTransformer)
  }
  
  // MARK: Error helpers
  
  fileprivate func errorTransformer(_ error: ErrorResponse) -> ApiError {
    return .networkingError(error.result as NSError)
  }
    
  // ...
}

Where ApiError is:

import Foundation
import Statham

public enum ApiError : Error {
  case notFound
  case networkingError(NSError)
  case jsonDecodingError(Error)
}

extension ApiError: CustomStringConvertible {
  public var description: String {
    switch self {
    case .notFound: return NSLocalizedString("Not Found", comment: "Api Error: resource not found")
    case .networkingError(let error): return error.localizedDescription
    case .jsonDecodingError(let error):
      #if DEBUG
        if let error = error as? JsonDecodeError {
          print(error.fullDescription)
        }
      #endif
      return NSLocalizedString("Server error", comment: "Api Error: Server error")
    }
  }
}

The problem comes when using .mapError(), where the compiler complains about "Argument passed to call that takes no arguments". Digging in the github, I can see that indeed there is this following method mapError() that does not take any arguments and that is a new addition since the 0.5.0 version.

I can see however the right method here, but it seems that extension is sort of overriding the right one? Or am I missing something important here?

[tomlokhorst]

The swift compiler often shows the "wrong" type of error in case of a type error.

Looking at your code, I'm guessing you're using the responseJSONPromise from the Alamofire extension. That returns a Promise<SuccessResponse<Any>, ErrorResponse>, not a Promise<SuccessResponse<AnyObject>, ErrorResponse> as you're using here.

[pablorecio]

Wow, Xcode does not help sometimes.

Thank you.