Type-wrapper for dataTaskWithRequest

NSURLSession+DataTaskResult.swift

// known-good: Xcode 7.3, Swift 2.2

import Foundation

public enum DataTaskResult {
  case Success(data:NSData,response:NSURLResponse?)
  case Error(error:NSError,response:NSURLResponse?)
}

extension NSURLSession {
  public func dataTaskWithRequest(request:NSURLRequest,
                                  completion:(DataTaskResult)->Void) -> NSURLSessionDataTask
  {
    let t = self.dataTaskWithRequest(request) { (data, response, error) in
      if let data = data {
        completion(DataTaskResult.Success(data: data, response: response))
      }
      else if let error = error {
        completion(DataTaskResult.Error(error: error, response: response))
      }
      else {
        NSLog("ERROR: NSURLSession.dataTaskWithRequest(_:completion:) has violated its API contract by returning a result that contains neither an NSError nor an NSData.")
        let err = NSError(domain: "com.alexisgallagher.dataTaskWithRequest", code: 10, userInfo:
          [NSLocalizedFailureReasonErrorKey : "NSURLSession.dataTaskWithRequest(_:completion:) has violated its API contract by returning a result that contains neither an NSError nor an NSData.","result":response ?? NSNull()])
        completion(DataTaskResult.Error(error:err, response: response))
      }
    }
    return t
  }
}