How would you design a plugin system using interfaces?

Short answer: Define an interface like IPlugin with a Run() method.

Explain a bit more

Each plugin implements IPlugin and can be loaded dynamically. interface IPlugin { void Run(); } class PluginA : IPlugin { public void Run() => Console.WriteLine("Plugin A running"); } class PluginB : IPlugin { public void Run() => Console.WriteLine("Plugin B running"); } // Usage List<IPlugin> plugins = new List<IPlugin> { new PluginA(), new PluginB() }; foreach (var p in plugins) p.Run();

Example code

Define an interface like IPlugin with a Run() method. Each plugin implements IPlugin and can be loaded dynamically. interface IPlugin { void Run(); }
class PluginA : IPlugin { public void Run() => Console.WriteLine("Plugin A running"); } class PluginB : IPlugin { public void Run() => Console.WriteLine("Plugin B running"); } // Usage List<IPlugin> plugins = new List<IPlugin> { new PluginA(), new PluginB() }; foreach (var p in plugins) p.Run();

Real-world example (ShopNest)

Checkout calls IPaymentGateway.Charge(). Razorpay and Stripe adapters implement the same interface, so ShopNest can switch gateways without rewriting the order service.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.