Clean Architecture

Clean Architecture separates code into layers: Presentation → Domain ← Data. Dependencies point inward.

Presentation Layer

• ViewModels must use @Observable (not ObservableObject) and be marked @MainActor.
• Views must be purely declarative – no business logic, no direct API calls, no database access.
• ViewModels must call Use Cases from Domain, never directly access repositories or network clients.
• Use @State for view-local UI state only (sheet presentation, focus), not domain data.
• Inject dependencies through initializers, never use singletons like NetworkManager.shared.
• ViewModels should expose private(set) state – views read, ViewModels write.

Domain Layer

• Entities must be pure Swift with no framework imports (no import SwiftUI, no import SwiftData).
• Mark entities as Sendable when passed across concurrency boundaries.
• Never add Codable to domain entities – use separate DTOs in Data layer.
• Use Cases must encapsulate single operations: GetProductsUseCase, AddToCartUseCase.
• Repository protocols belong in Domain, implementations in Data (dependency inversion).
• Domain layer must have zero dependencies on other layers.

Data Layer

• Repository implementations must map between DTOs and Domain entities.
• Never expose DTOs to Domain or Presentation layers.
• If using SwiftData, never mark @Model classes as Sendable – this causes runtime crashes.
• All SwiftData ModelContext operations must be on @MainActor.
• Repository implementations using SwiftData must be marked @MainActor.
• Keep SwiftData models in Data layer, separate from Domain entities.

Common Violations

Flag these architectural violations:

• ViewModel calling API client directly instead of Use Case
• Domain entities importing SwiftUI or SwiftData
• SwiftData @Model classes marked as Sendable
• Repository implementations in Presentation layer
• Business logic in Views or ViewModels instead of Use Cases
• Singletons (.shared) used for testable dependencies
• DTOs exposed to Presentation layer
• Domain entities with Codable conformance

Dependency Injection

• Create all dependencies at app entry point (Composition Root in @main struct).
• Use @Environment to pass dependencies down view hierarchy.
• Inject protocols, not concrete types, to enable mocking in tests.