Как организовать сетевой слой на URLSession без сторонних библиотек?

enum API {
    	case getUsers, getPosts(userId: Int)

    	var urlRequest: URLRequest {
        	var url = URL(string: "https://api.example.com")!
        	switch self {
        	case .getUsers:
            		url.appendPathComponent("/users")
        	case .getPosts(let id):
            		url.appendPathComponent("/posts")
            		url = URL(string: "\(url)?userId=\(id)")!
        	}
        	var req = URLRequest(url: url)
        	req.httpMethod = "GET"
        	req.setValue("application/json", forHTTPHeaderField: "Accept")
        	return req
    	}
}

class NetworkManager {
    	private let session = URLSession.shared

    	func request<T: Decodable>(_ api: API, completion: @escaping (Result<T, Error>) -> Void) {
        	let task = session.dataTask(with: api.urlRequest) { data, res, err in
            		if let e = err { return completion(.failure(e)) }
            		guard let d = data else { return /* ошибка */ }
            		do {
                		let obj = try JSONDecoder().decode(T.self, from: d)
                		completion(.success(obj))
            		} catch {
                		completion(.failure(error))
            		}
        	}
        	task.resume()
    	}
}

let nm = NetworkManager()
nm.request(.getUsers) { (result: Result<[User], Error>) in
    	switch result {
    	case .success(let users): print(users)
    	case .failure(let err): print(err)
    	}
}