class APIClient {
    let urlSession = URLSession(configuration: .default)
    func perform(_ urlRequest: URLRequest,
                 completion: @escaping (Data?, URLResponse?, Error?) -> Void) {
        let urlSessionTask =
            urlSession
                .dataTask(with: urlRequest) { [weak self] (data, response, error) in
                    completion(data, response, error)
        }
        urlSessionTask?.resume()
    }
}