Swinject
Dependency injection framework for Swift and Objective-C. Swinject provides a DI Container with type-safe registration and resolution: container.register(AgentProtocol.self) { _ in RealAgent() }, container.resolve(AgentProtocol.self). Supports named registrations for multiple implementations, object scopes (transient, container, graph, weak), circular dependency detection, and SwinjectStoryboard for UIKit storyboard DI. Works alongside Swift's protocol-oriented design — register protocols, resolve implementations. Enables testability by swapping real agent implementations with mocks by registering different types in test container.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
DI framework — no network exposure. Dependency container can be used to inject security-sensitive services; ensure mock/test registrations never leak into production build. Container-scoped singleton agent auth services should be carefully lifecycle managed.
⚡ Reliability
Best When
You're building an iOS/macOS agent app with complex dependency graphs that need to be swapped for testing — Swinject provides clean DI container with protocol-based resolution that makes agent services testable.
Avoid When
Your app is simple enough for SwiftUI @Environment injection, you need compile-time dependency verification (use Needle), or you're not targeting Apple platforms.
Use Cases
- • Wire agent service dependencies in iOS app — Container registers AgentNetworkService, AgentCacheService, AgentRepository; ViewModel resolved with all dependencies injected; test uses mock registrations for isolated agent unit tests
- • Feature flag-based agent implementation switching — container.register(AgentService.self) { _ in featureFlags.newAgent ? NewAgentService() : LegacyAgentService() } for runtime agent implementation selection
- • Named registrations for multiple agent implementations — container.register(AgentProtocol.self, name: 'fast') { _ in FastAgent() } and register(AgentProtocol.self, name: 'accurate') { _ in AccurateAgent() }
- • Scoped agent services with container scope — .inObjectScope(.container) creates singleton agent service per Container; .inObjectScope(.transient) creates new instance per resolution for stateful agent components
- • Assembly pattern for modular agent DI — separate Assembly classes for each feature module (AgentAssembly, NetworkAssembly, AnalyticsAssembly) assembled into root Container at app startup
Not For
- • Teams using Swift's @Observable and dependency injection via environment — modern SwiftUI apps can use @Environment and @Observable for lightweight DI without Swinject; evaluate fit before adding framework dependency
- • Compile-time DI verification — Swinject resolves dependencies at runtime; resolution failure throws at runtime not compile time; use Needle (by Uber) for compile-time checked DI in large iOS agent apps
- • Android/cross-platform — Swinject is iOS/macOS only; use Hilt (Android) or Koin (Kotlin Multiplatform) for agent apps needing cross-platform DI
Interface
Authentication
DI framework — no auth concepts. Auth services registered as dependencies in Container like any other agent service.
Pricing
Swinject is MIT licensed, community-maintained. Free for all use including commercial apps.
Agent Metadata
Known Gotchas
- ⚠ Runtime resolution failure returns nil — container.resolve(AgentService.self) returns nil if not registered; missing registration in agent app delegate setup causes nil service silently; use container.resolve(AgentService.self)! only if 100% certain it's registered, or add precondition with clear message
- ⚠ Circular dependencies cause infinite loop — Swinject detects some circular dependencies but not all patterns; A depends on B, B depends on A causes stack overflow; redesign agent service graph to break cycles with lazy injection or initialization injection pattern
- ⚠ Assembly registration order matters for overrides — registering same type twice keeps last registration; in test assemblies that override production assemblies, register test implementations after production assembly; wrong order uses production agent implementations in tests
- ⚠ Thread safety requires explicit synchronization — Swinject Container is not thread-safe by default; concurrent resolve() calls from background agent threads require thread-safe container wrapper (Swinject's ThreadSafeResolver) or single-threaded DI resolution at startup
- ⚠ Object scope graph prevents cycles in tree resolution — .inObjectScope(.graph) shares instance within single resolve() call tree; useful for agent factory methods that should share a single instance during construction but create new instance per top-level resolve
- ⚠ SwinjectStoryboard requires registration before storyboard loads — SwinjectStoryboard must have Container registered before first storyboard instantiation; late registration (after viewDidLoad) causes nil injection for agent view controllers loaded from storyboard
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Swinject.
Scores are editorial opinions as of 2026-03-06.