Decorator pattern

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Description

Attach additional responsibilities to an object dynamically.
Decorators provide a flexible alternative to subclassing for extending functionality

  • Add new functionalities dynamically to existing objects
  • The object does not know it is being « decorated »
  • Decorators both inherit the original class and contain an instantiation of it
  • It is an alternative to subclass to add new functionalities

Exemple

IUser.cs
public interface IUser
{
    string Name { get; set; }
}
User.cs
public class User : IUser
{
    public string Name { get; set; }

    public User(string name)
    {
        this.Name = name;
    }
}
UserTitle.cs
public class UserTitle : IUser
{
    private IUser user;

    public string Name
    {
        get => $"{user.Name} ({Title})";
        set => user.Name = value;
    }

    public string Title { get; set; }

    public UserTitle(IUser user, string title)
    {
        this.user = user;
        this.Title = title;
    }
}
UserEmail.cs
public class UserEmail : IUser
{
    private IUser user;

    public string Name
    {
        get => $"{user.Name} - {Email}";
        set => user.Name = value;
    }

    public string Email { get; set; }

    public UserEmail(IUser user, string email)
    {
        this.user = user;
        this.Email = email;
    }
}
Csharp.svg
var user = new User("Nicolas");
Console.WriteLine(user.Name);  // Nicolas

var userWithTitle = new UserTitle(user, "Big Boss");
Console.WriteLine(userWithTitle.Name);  // Nicolas (Big Boss)

var userWithEmail = new UserEmail(user, "nicolas@world-company.net");
Console.WriteLine(userWithEmail.Name);  // Nicolas (Big Boss) - nicolas@world-company.net