Generate your own Error code in swift 3

In your case, the error is that you're trying to generate an Error instance. Error in Swift 3 is a protocol that can be used to define a custom error. This feature is especially for pure Swift applications to run on different OS.

In iOS development the NSError class is still available and it conforms to Error protocol.

So, if your purpose is only to propagate this error code, you can easily replace

var errorTemp = Error(domain:"", code:httpResponse.statusCode, userInfo:nil)

with

var errorTemp = NSError(domain:"", code:httpResponse.statusCode, userInfo:nil)

Otherwise check the Sandeep Bhandari's answer regarding how to create a custom error type

You can create a protocol, conforming to the Swift LocalizedError protocol, with these values:

protocol OurErrorProtocol: LocalizedError {

    var title: String? { get }
    var code: Int { get }
}

This then enables us to create concrete errors like so:

struct CustomError: OurErrorProtocol {

    var title: String?
    var code: Int
    var errorDescription: String? { return _description }
    var failureReason: String? { return _description }

    private var _description: String

    init(title: String?, description: String, code: Int) {
        self.title = title ?? "Error"
        self._description = description
        self.code = code
    }
}

You should use NSError object.

let error = NSError(domain: "", code: 401, userInfo: [ NSLocalizedDescriptionKey: "Invalid access token"])

Then cast NSError to Error object.

You can create enums to deal with errors :)

enum RikhError: Error {
    case unknownError
    case connectionError
    case invalidCredentials
    case invalidRequest
    case notFound
    case invalidResponse
    case serverError
    case serverUnavailable
    case timeOut
    case unsuppotedURL
 }

and then create a method inside enum to receive the http response code and return the corresponding error in return :)

static func checkErrorCode(_ errorCode: Int) -> RikhError {
        switch errorCode {
        case 400:
            return .invalidRequest
        case 401:
            return .invalidCredentials
        case 404:
            return .notFound
        //bla bla bla
        default:
            return .unknownError
        }
    }

Finally update your failure block to accept single parameter of type RikhError :)

I have a detailed tutorial on how to restructure traditional Objective - C based Object Oriented network model to modern Protocol Oriented model using Swift3 here https://learnwithmehere.blogspot.in Have a look :)

Hope it helps :)