AlamofireArgoExtension.swift

extension Alamofire.Request {
    public func responseObject<T: Decodable where T == T.DecodedType>(completionHandler: Response<T, NSError> -> Void) -> Self {
        let responseSerializer = ResponseSerializer<T, NSError> { request, response, data, error in
            guard error == nil else { return .Failure(error!) }
            
            let JSONResponseSerializer = Request.JSONResponseSerializer(options: .AllowFragments)
            let result = JSONResponseSerializer.serializeResponse(request, response, data, error)
            
            switch result {
            case .Success(let value):
                let decoded: Decoded<T> = decode(value)
                switch decoded {
                case .Success(let object):
                    return .Success(object)
                case .Failure(.MissingKey(let key)):
                    return .Failure(Error.errorWithCode(.JSONSerializationFailed, failureReason: "Missing key \(key): \(value)"))
                case .Failure(.TypeMismatch(let type)):
                    return .Failure(Error.errorWithCode(.JSONSerializationFailed, failureReason: "Type mismatch for \(type): \(value)"))
                }
            case .Failure(let error):
                return .Failure(error)
            }
        }
        return response(responseSerializer: responseSerializer, completionHandler: completionHandler)
    }
}