Why should you care?

ShopNest “OrderPaidAlert” should work over Email or Slack without a class explosion.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

public interface IMessageSender { void Send(string msg); }
public sealed class EmailSender : IMessageSender
{
    public void Send(string msg) => Console.WriteLine($"email: {msg}");
}
public abstract class Alert
{
    protected readonly IMessageSender Sender;
    protected Alert(IMessageSender sender) => Sender = sender;
    public abstract void Notify(string text);
}
public sealed class OrderPaidAlert : Alert
{
    public OrderPaidAlert(IMessageSender sender) : base(sender) { }
    public override void Notify(string text) => Sender.Send($"PAID {text}");
}

new OrderPaidAlert(new EmailSender()).Notify("Order 9");

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Alert hierarchy is the abstraction; IMessageSender is the implementation.
• Mix OrderPaidAlert with SlackSender later without new subclasses for every pair.

Practice next

1. Run OrderPaidAlert with EmailSender.
2. Add SlackSender and reuse OrderPaidAlert.
3. Add RefundAlert sharing the same senders.
4. Inject IMessageSender via DI.
5. Add SmsSender.

Remember

Abstraction ⟂ implementation. Avoid Cartesian subclass growth. Inject the implementor.

ShopNest alert bridge

Ops chooses Slack vs Email per environment.

Outcome: Same alert types; different transports.