1public interface IUserService
2{
3    User GetUserById(int userId);
4    void AddUser(User user);
5    void UpdateUser(User user);
6    void DeleteUser(int userId);
7}

1public class UserServiceImpl : IUserService
2{
3    private Dictionary<int, User> users;
4
5    public UserServiceImpl()
6    {
7        users = new Dictionary<int, User>();
8    }
9
10    public User GetUserById(int userId)
11    {
12        return users.ContainsKey(userId) ? users[userId] : null;
13    }
14
15    public void AddUser(User user)
16    {
17        users[user.Id] = user;
18    }
19
20    public void UpdateUser(User user)
21    {
22        if (users.ContainsKey(user.Id))
23        {
24            users[user.Id] = user;
25        }
26    }
27
28    public void DeleteUser(int userId)
29    {
30        users.Remove(userId);
31    }
32}

1public class LoggingUserService : IUserService
2{
3    private IUserService userService;
4
5    public LoggingUserService(IUserService userService)
6    {
7        this.userService = userService;
8    }
9
10    public User GetUserById(int userId)
11    {
12        Log("GetUserById");
13        return userService.GetUserById(userId);
14    }
15
16    public void AddUser(User user)
17    {
18        Log("AddUser");
19        userService.AddUser(user);
20    }
21
22    public void UpdateUser(User user)
23    {
24        Log("UpdateUser");
25        userService.UpdateUser(user);
26    }
27
28    public void DeleteUser(int userId)
29    {
30        Log("DeleteUser");
31        userService.DeleteUser(userId);
32    }
33
34    private void Log(string action)
35    {
36        Console.WriteLine($"Logging: User Service - {action}");
37    }
38}

1public class Program
2{
3    public static void Main()
4    {
5        // ایجاد سرویس اصلی
6        IUserService userService = new UserServiceImpl();
7
8        // ایجاد سرویس با قابلیت لاگ کردن
9        IUserService loggingUserService = new LoggingUserService(userService);
10
11        // مدیریت کاربران با ویژگی لاگ کردن
12        loggingUserService.AddUser(new User(1, "John"));
13        loggingUserService.UpdateUser(new User(1, "John Doe"));
14        loggingUserService.DeleteUser(1);
15    }
16}

Logging: User Service - AddUser
Logging: User Service - UpdateUser
Logging: User Service - DeleteUser