Swift - 修改变量

Question

我有一个简单的功能，只有一个例外。

static func configSessionAndSend(request: URLRequest) -> Character {
        // Create and run a URLSession data task with our JSON encoded POST request
        var responseChar: Character = "1"
        let config = URLSessionConfiguration.default
        let session = URLSession(configuration: config)
        let task = session.dataTask(with: request) { (responseData, response, responseError) in
            guard responseError == nil else {
                //TODO: error handling
                return
            }

            // APIs usually respond with the data you just sent in your POST request

            if let data = responseData, let utf8Representation = String(data: data, encoding: .utf8), let httpUrlResponse = response as? HTTPURLResponse {

                responseChar = StringHelper.getSecondLetter(stringValue: utf8Representation)
                print("response: ", utf8Representation) //print server response
                //print(httpUrlResponse.allHeaderFields) //print server headers
                print("server response status: ", httpUrlResponse.statusCode) //print status code; use this later to check if 200 all OK
                print("server respose char: ", responseChar)
            } else {
                print("no readable data received in response")

            }
        }

        task.resume()
        return responseChar

    }

我的服务器应该返回0，并且我修改了变量responseChar，print("server respose char: ", responseChar)在if语句内部时给出了正确的值。但是return responseChar返回1，就像我的初始变量从未被修改过一样？我做错了什么？