URLSessionWithResult.playground

import UIKit

extension URLSession {
    func dataTask(with url: URL, completionHandler: @escaping (Result<Data, Error>, URLResponse?) -> Void) -> URLSessionDataTask {
        return dataTask(with: url) { (data, response, error) in
            if let error = error {
                completionHandler(.failure(error), response)
            } else {
                completionHandler(.success(data ?? Data()), response)
            }
        }
    }
}

extension Result where Success == Data {
    func decode<T: Decodable>(with decoder: JSONDecoder = .init()) -> Result<T, Error> {
        do {
            let data = try get()
            let decoded = try decoder.decode(T.self, from: data)
            return .success(decoded)
        } catch {
            return .failure(error)
        }
    }
}

class History: Decodable {
    var id = 0
}

class HistoryService {
    private let session: URLSession
    private let decoder: JSONDecoder
    
    init(session: URLSession, decoder: JSONDecoder) {
        self.session = session
        self.decoder = decoder
    }
    
    let url = URL(string: "https://xxxx.com/history/")!
    
    func fetch(handler: @escaping (Result<History, Error>) -> Void) {
        let task = session.dataTask(with: url) { (result, response) in
            handler(result.decode())
        }
        task.resume()
    }
}

let service = HistoryService(session: URLSession.shared, decoder: JSONDecoder())
service.fetch { (result) in
    switch result {
    case .success(let history):
        print(history.id)
    case .failure(let error):
        print(error.localizedDescription)
    }
}