SwiftUI Modular MVVM-C Architecture

Opinionated architecture enforcement for SwiftUI clinic-style apps. This skill aligns to the iOS 26 / Swift 6.2 clinic architecture: modular MVVM-C in local SPM packages, concrete coordinators and route shells in the App target, pure Domain protocols, and Data as the only I/O layer.

Mandated Architecture Stack

┌───────────────────────────────────────────────────────────────┐
│ App target: DependencyContainer, Coordinators, Route Shells   │
├───────────────┬───────────────┬───────────────┬──────────────┤
│ Feature* SPM  │ Feature* SPM  │ Feature* SPM  │ Feature* SPM │
│ View + VM     │ View + VM     │ View + VM     │ View + VM    │
├───────────────────────────────────────────────────────────────┤
│ Data SPM: repository impls, remote/local, retry, sync queue   │
├───────────────────────────────────────────────────────────────┤
│ Domain SPM: models, repository protocols, coordinator protocols│
│ and ErrorRouting/AppError                                      │
├───────────────────────────────────────────────────────────────┤
│ Shared SPMs: DesignSystem, SharedKit                           │
└───────────────────────────────────────────────────────────────┘

Dependency Rule: Feature modules import

Domain

DesignSystem

Data

Clinic Architecture Contract (iOS 26 / Swift 6.2)

All guidance in this skill assumes the clinic modular MVVM-C architecture:

• Feature modules import

  Domain

  +

  DesignSystem

  only (never

  Data

  , never sibling features)
• App target is the convergence point and owns

  DependencyContainer

  , concrete coordinators, and Route Shell wiring

• Domain

  stays pure Swift and defines models plus repository,

  *Coordinating

  ,

  ErrorRouting

  , and

  AppError

  contracts

• Data

  owns SwiftData/network/sync/retry/background I/O and implements Domain protocols
• Read/write flow defaults to stale-while-revalidate reads and optimistic queued writes
• ViewModels call repository protocols directly (no default use-case/interactor layer)

When to Apply

Reference these guidelines when:

• Building or refactoring feature modules under local SPM packages
• Wiring coordinators, route shells, and dependency container factories
• Defining Domain protocols for repositories, coordinators, and error routing
• Enforcing Data-only ownership of networking, persistence, and sync
• Reviewing stale-while-revalidate reads and optimistic queued writes

Non-Negotiable Constraints (iOS 26 / Swift 6.2)

• @Observable

  for ViewModels/coordinators,

  ObservableObject

  /

  @Published

  never
• No dedicated use-case/interactor layer: ViewModels call Domain repository protocols directly
• Coordinator protocols live in Domain; concrete coordinators own

  NavigationPath

  in App target
• Route shells live in App target and own

  .navigationDestination

  mapping

• AppError

  +

  ErrorRouting

  drive presentation policy; ViewModels do not hardcode global error UI
• SwiftData / URLSession / retry / sync queue logic stays in Data package only

Rule Categories by Priority

diff-

state-

view-

nav-

layer-

di-

list-

data-

Quick Reference

1. View Identity & Diffing (CRITICAL)

• diff-equatable-views

  - Apply @Equatable macro to every SwiftUI view

• diff-closure-skip

  - Use @SkipEquatable for closure/handler properties

• diff-reference-types

  - Never store reference types without Equatable conformance

• diff-identity-stability

  - Use stable O(1) identifiers in ForEach

• diff-avoid-anyview

  - Never use AnyView — use @ViewBuilder or generics

• diff-printchanges-debug

  - Use _printChanges() to diagnose unnecessary re-renders

2. State Architecture (CRITICAL)

• state-observable-class

  - Use @Observable classes for all ViewModels

• state-ownership

  - @State for owned data, plain property for injected data

• state-single-source

  - One source of truth per piece of state

• state-scoped-observation

  - Leverage @Observable property-level tracking

• state-binding-minimal

  - Pass @Binding only for two-way data flow

• state-environment-global

  - Use @Environment for app-wide shared dependencies

• state-no-published

  - Never use @Published or ObservableObject

3. View Composition (HIGH)

• view-body-complexity

  - Maximum 10 nodes in view body

• view-extract-subviews

  - Extract computed properties/helpers into separate View structs

• view-no-logic-in-body

  - Zero business logic in body

• view-minimal-dependencies

  - Pass only needed properties, not entire models

• view-viewbuilder-composition

  - Use @ViewBuilder for conditional composition

• view-no-init-sideeffects

  - Never perform work in View init

4. Navigation & Coordination (HIGH)

• nav-coordinator-pattern

  - Every feature has a coordinator owning NavigationStack

• nav-routes-enum

  - Define all routes as a Hashable enum

• nav-deeplink-support

  - Coordinators must support URL-based deep linking

• nav-modal-sheets

  - Present modals via coordinator, not inline

• nav-no-navigationlink

  - Never use NavigationLink(destination:) — use navigationDestination(for:)

5. Layer Architecture (HIGH)

• layer-dependency-rule

  - Domain layer has zero framework imports

• layer-usecase-protocol

  - Do not add a use-case layer; keep orchestration in ViewModel + repository protocols

• layer-repository-protocol

  - Repository protocols in Domain, implementations in Data

• layer-model-value-types

  - Domain models are structs, never classes

• layer-no-view-repository

  - Views never access repositories directly; ViewModel calls repository protocols

• layer-viewmodel-boundary

  - ViewModels expose display-ready state only

6. Dependency Injection (MEDIUM-HIGH)

• di-environment-injection

  - Inject container-managed protocol dependencies via @Environment

• di-protocol-abstraction

  - All injected dependencies are protocol types

• di-container-composition

  - Compose

  DependencyContainer

  in App target and expose VM factories

• di-mock-testing

  - Every protocol dependency has a mock for testing

7. List & Collection Performance (MEDIUM)

• list-constant-viewcount

  - ForEach must produce constant view count per element

• list-filter-in-model

  - Filter/sort in ViewModel, never inside ForEach

• list-lazy-stacks

  - Use LazyVStack/LazyHStack for unbounded content

• list-id-keypath

  - Provide explicit id keyPath — never rely on implicit identity

8. Async & Data Flow (MEDIUM)

• data-task-modifier

  - Use

  .task(id:)

  as the primary feature data-loading trigger

• data-async-init

  - Never perform async work in init

• data-error-loadable

  - Model loading states as enum, not booleans

• data-combine-avoid

  - Prefer async/await over Combine for new code

• data-cancellation

  - Use .task automatic cancellation — never manage Tasks manually

How to Use

Read individual reference files for detailed explanations and code examples:

• Section definitions - Category structure and impact levels
• Rule template - Template for adding new rules

Reference Files