What is the difference between IActionResult and ActionResult<T>?

Short answer: IActionResult: Represents a non-generic result of an action method. Can return any HTTP response (Ok, NotFound, Redirect, etc.). ActionResult<T>: Combines a result with a typed value (T). It allows returning typed data or an HTTP response. Improves clarity and enables better OpenAPI docs.

Real-world example (ShopNest)

ShopNest registers AppDbContext as Scoped and IMemoryCache as Singleton. Putting DbContext in a Singleton causes threading bugs.

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.