How to use throw from within do block?

Question

I would like to throw error from within do block, if that is possible

I have a function getWeatherBy, it is signed as a throwing function. My code elsewhere in the app is depending on this throwing. I have inside of this function a JSONDecoder.decode that is throwing function itself, I have that inside of a do block. However, if there is an error with JSONDecoder, I would like to throw error from getWeatherBy, but since that throwing is happening inside of a JSONDecoder, it is being catched there.

Sorry for the messy code. I am still a newbie, any ideas how to make this code better is more than welcomed!

func getWeatherBy(city: String, completion: ((WeatherRecord) -> ())?) throws {
        let trimmedCityName = (city as NSString).replacingOccurrences(of: " ", with: "+")
        
        let url = URL(string: "https://api.openweathermap.org/data/2.5/weather?q=\(trimmedCityName.lowercased())&appid=\(self.OpenWeatherAPIkey)&units=metric")
        guard url != nil else { return }
        print(url!)

        let networkTask: URLSessionDataTask = URLSession.shared.dataTask(with: url!) {
            (data, response, error) in
            guard let data = data else { return }
            
            do {
                let decoded = try JSONDecoder().decode(WeatherData.self, from: data)
                if (decoded.main != nil) {
                    if (decoded.coord?.lat != nil) {
                        DispatchQueue.main.async {
                            let record = WeatherRecord(temperature: Float(decoded.main!.temp), date: Date(), coordinates: CLLocationCoordinate2D(latitude: decoded.coord!.lat, longitude: decoded.coord!.lon), distance: 0.0)
                            
                            if completion != nil {
                                completion!(record)
                                
                            }
                        }
                    }
                } else {
                    throw serviceError.cityNotFound
                }
                
                if (decoded.message != nil) {
                    print("Message: \(decoded.message!)")
                    
                    DispatchQueue.main.async {
                        if (String(describing: decoded.message!).contains("Your account is temporary blocked") == true) {
                            
                        }
                        
                        if (decoded.message! != "Nothing to geocode") || String(describing: decoded.message!).contains("Your account is temporary blocked") != false {
                            
                        }
                    }
                }
            } catch DecodingError.keyNotFound(let key, let context) {
                Swift.print("Could not find key \(key) in JSON: \(context.debugDescription)")
            } catch DecodingError.valueNotFound(let type, let context) {
                Swift.print("Could not find type \(type) in JSON: \(context.debugDescription)")
            } catch DecodingError.typeMismatch(let type, let context) {
                Swift.print("Type mismatch for type \(type) in JSON: \(context.debugDescription) \(context)")
            } catch DecodingError.dataCorrupted(let context) {
                Swift.print("Data found to be corrupted in JSON: \(context.debugDescription)")
            } catch let error as NSError {
                NSLog("Error in read(from:ofType:) domain= \(error.domain), description= \(error.localizedDescription)")
            }
        }

Answer 1

The most common way is to add an error with / without new Result

func getWeatherBy(city: String, completion: ((WeatherRecord? , Error?) -> ()))

you can't throw from an asynchronous method immediately