What are Clean Architecture and the Dependency Rule?

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The point

Clean Architecture (Robert Martin) is a way to organize code into concentric layers with business rules in the center and details outside:

1. Entities — domain models and rules (Account, Money).
2. Use Cases (Interactors) — application scenarios: "withdraw money", "place an order".
3. Interface Adapters — Presenter/ViewModel, Repository implementations, DTO-to-Entity mappers.
4. Frameworks & Drivers — UIKit/SwiftUI, URLSession, SwiftData/Core Data, SDKs.

Dependency Rule: source code may depend only inward. A Use Case does not know that data comes from URLSession, nor that the UI is SwiftUI. For an inner layer to call an outer one (save to a DB) it declares a port — a protocol — and the outer layer implements it. This is DIP at the scale of the whole app.