dependency-injection

name	dependency-injection
description	Creates Features for dependency injection. Use when creating features, exposing public entry points, or wiring up dependencies.

Skill: Dependency Injection

Guide for creating dependency injection with Composition Root pattern.

References

• AppContainer (Composition Root, RootContainerView): See references/app-container.md
• Feature & Container (Feature struct, Container, navigation, simple feature): See references/feature-container.md
• Tests (feature tests, generic pattern): See references/tests.md

---

Architecture Overview

ChallengeApp
    │
    └── AppContainer (Composition Root)
        │
        ├── httpClient: HTTPClientContract
        ├── tracker: TrackerContract
        ├── imageLoader: ImageLoaderContract → SwiftUI Environment
        │
        └── features: [Feature]
            ├── CharacterFeature (navigation + deep links)
            │   └── CharacterContainer (DI composition)
            │       ├── repository
            │       ├── makeCharacterListView()
            │       └── makeCharacterDetailView()
            │
            └── HomeFeature (navigation)
                └── HomeContainer (DI composition)
                    └── makeHomeView()

---

Key Concepts

• AppContainer: Composition Root — creates shared dependencies (HTTPClient, Tracker) and all features
• {Feature}Container: Handles dependency composition (repositories, factories)
• {Feature}Feature: Handles navigation and deep links, delegates DI to Container
• Container factory methods create both ViewModel and View — callers receive a ready-to-use some View
• Navigation is handled by App using NavigationCoordinator

---

File Structure

App/
├── Sources/
│   └── {AppName}App.swift

AppKit/
├── Sources/
│   ├── AppContainer.swift
│   ├── Presentation/
│   │   ├── Navigation/
│   │   │   └── AppNavigationRedirect.swift
│   │   └── Views/
│   │       ├── NavigationContainerView.swift
│   │       ├── RootContainerView.swift
│   │       └── ModalContainerView.swift

Features/{Feature}/
├── Sources/
│   ├── {Feature}Feature.swift
│   ├── {Feature}Container.swift
│   ├── Navigation/
│   │   ├── {Feature}IncomingNavigation.swift
│   │   ├── {Feature}OutgoingNavigation.swift
│   │   └── {Feature}DeepLinkHandler.swift
│   └── Presentation/
│       └── {Screen}/
│           ├── Navigator/
│           ├── Tracker/
│           ├── Views/
│           └── ViewModels/
└── Tests/
    └── Feature/
        └── {Feature}FeatureTests.swift

---

Dependency Patterns

Type	Pattern	Reason
HTTPClient	Required init parameter	Injected by AppContainer
Tracker	Required init parameter	Injected by AppContainer
ImageLoader	SwiftUI Environment	Injected by RootContainerView from AppContainer
Container	Created in Feature init	Owns dependency composition
DataSource	Local variable in Container init	Only needed to build repositories
Repository	Stored property in Container (let)	Built in init, used by factory methods
Navigator	Created inline inside Container factory method	New instance per View
Screen Tracker	Created inline inside Container factory method	New instance per View
ViewModel	Created inline inside Container factory method	New instance per View
View	Container factory method (make{Name}View)	Wraps ViewModel; returned as some View
UseCase	Created inline	Stateless

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Visibility Summary

Component	Visibility	Reason
Contract (Protocol)	public	API for consumers, enables DI
{Feature}Feature	public	Entry point struct
{Feature}Container	internal	Created by Feature within same module
Feature.makeMainView()	public	Creates the feature's default entry point
Feature.resolve()	public	Returns view for navigation or nil
AppContainer.init	public	Only public member, created by ChallengeApp
AppContainer methods	internal/private	resolveView, handle, makeRootView are internal; rest private
Container factory methods (make{Name}View)	internal	Called by Feature; return some View
{Feature}IncomingNavigation	public	Used by AppNavigationRedirect
{Feature}OutgoingNavigation	public	Used by AppNavigationRedirect
{Feature}DeepLinkHandler	internal	Accessed via Feature.deepLinkHandler
Navigator / Tracker / Views	internal	Internal to feature

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Checklist

• Create AppContainer.swift in AppKit/Sources/ as Composition Root
• Create AppNavigationRedirect.swift in AppKit/Sources/Presentation/Navigation/
• Create RootContainerView.swift in AppKit/Sources/Presentation/Views/
• Create {Feature}Container.swift for dependency composition
• Create {Feature}Feature.swift as struct implementing FeatureContract protocol
• Feature requires httpClient and tracker in init
• Feature creates Container in init, passing tracker
• Container builds DataSources as local variables in init
• Container has stored repository properties (private let)
• Container has factory methods (make{Name}View) receiving navigator: any NavigatorContract, returning some View
• Create {Feature}IncomingNavigation.swift
• Create {Feature}OutgoingNavigation.swift for cross-feature navigation (if needed)
• Create {Feature}DeepLinkHandler.swift (only if feature handles deep links)
• Add feature to AppContainer.features array
• ChallengeApp imports ChallengeAppKit and uses RootContainerView
• Create feature tests