swift3 - Callback syntax in swift 3 -

i trying create callback on swift 3 haven't had luck far. taking @ question: link similar, answer gives me error.

basically have api struct static function need have callback.

import uikit  struct api {  public static func functionwithcallback(params: dictionary<string, string>, success: @escaping ((_ response: string) -> ticket), failure: @escaping((_ error:string) -> string) ) {         let app_server_url = "http://api.com" + params["key"]!          let url: url = url(string: app_server_url)!         var request: urlrequest = urlrequest(url: url)         request.httpmethod = "post"         {             request.httpbody = try jsonserialization.data(withjsonobject: params, options: .prettyprinted)          } catch let error {             print(error.localizeddescription)         }          request.addvalue("application/json charset=utf-8", forhttpheaderfield: "content-type")         request.addvalue("application/json charset=utf-8", forhttpheaderfield: "accept")          let session = urlsession.shared          let task = session.datatask(with: request urlrequest, completionhandler: { data, response, error in              guard error == nil else {                 return             }              guard let data = data else {                 return             }              dispatchqueue.main.async {                 {                     let json = try jsonserialization.jsonobject(with: data) as! [string: any]                     print(json)                     var message = ""                      if let result = json["result"] as? string {                         if(result == "success") {                             //attempt call callback gives me error: argument in call                             success("") {                                let ticket = json["ticket"] as! nsdictionary                                var date = ticket["date"] as! string                                var ticket: ticket = nil                                ticket.setdate(date: date)                                return ticket                             }                     }                     else {                         message = json["message"] as! string                         print(message)                     }                 } catch let error {                     print(error.localizeddescription)                      let description = error.localizeddescription                     if let data = description.data(using: .utf8) {                         {                             let jsonerror = try jsonserialization.jsonobject(with: data, options: []) as? [string: any]                             let message = jsonerror?["message"] as! string                         } catch {                          }                     }                 }             }         })         task.resume()     }  } 

so can't call callback success because gives me error: argument in call. idea on how fix it?

my goal call:

api.functionwithcallback(params: params, success() -> ticket {     //do returned ticket here }, error() -> () {    //do error message here } ) 

i believe have wrong on how use call closures, can understand of question want ticket in call closure , should parameter of closure not return type of closure.

replace function declaration this:

public static func functionwithcallback(params: dictionary<string, string>, success: @escaping ((_ response: string, _ ticket: ticket) -> void), failure: @escaping((_ error:string) -> void) ) { 

and inside function replace this:

success("") {     let ticket = json["ticket"] as! nsdictionary     var date = ticket["date"] as! string     var ticket: ticket = nil // im not sure trying line give error     ticket.setdate(date: date)     return ticket } 

with:

let ticket = json["ticket"] as! nsdictionary var date = ticket["date"] as! string var ticket: ticket = nil // fix line ticket.setdate(date: date) success("",ticket) 

and can call function this:

api.functionwithcallback(params: params, success: { response, ticket in     // can use ticket here     // , response text  }) { errormessage in     // use error message here }