How to Return JSON object from function in Swift

Question

I have a code to download a json data from web and pass it to a variable.

func getJson(url:String){
            let url = URL(string: url)!
            URLSession.shared.dataTask(with: url) {
                data, _, _ in
                if let data = data {
                    let json = try! JSONSerialization.jsonObject(with: data)
                    return json
                }
            }.resume()
        }

I don't know how to set a return value signature to this function