Golang / GoLang System Architecture and Testing Interview Questions

How do you manage dependency injection at scale in a large Go service — wire, dig, or manual?

As a Go service grows beyond a few dependencies, main() becomes a complex wiring function. Three approaches: manual wiring (always readable), Google Wire (code generation), or Uber Dig (reflection-based runtime injection).

// APPROACH 1: Manual wiring in main() â clear, no magic, preferred for < 20 deps
func main() {
    cfg, err := config.Load()
    if err != nil { log.Fatal(err) }

    db, err := database.Open(cfg.Database)
    if err != nil { log.Fatal(err) }

    userRepo  := postgres.NewUserRepository(db)
    emailSvc  := smtp.NewEmailService(cfg.SMTP)
    cacheSvc  := redis.NewCache(cfg.Redis)
    userSvc   := service.NewUserService(userRepo, emailSvc, cacheSvc)
    grpcSrv   := grpc.NewUserServer(userSvc)
    httpSrv   := http.NewServer(cfg.HTTP, userSvc)

    // Start servers...
}

// APPROACH 2: Wire (google/wire) â compile-time code generation
// wire.go (build tag: //go:build wireinject)
//go:build wireinject
func InitializeApp(cfgPath string) (*App, func(), error) {
    wire.Build(
        config.Provider,      // func LoadConfig() (*Config, error)
        database.Provider,    // func Open(*Config) (*sql.DB, error)
        postgres.NewUserRepository,
        smtp.NewEmailService,
        service.NewUserService,
        NewApp,
    )
    return nil, nil, nil // wire generates the real implementation
}
// Run: wire gen ./...  â generates wire_gen.go

// APPROACH 3: Dig (uber-go/dig) â runtime reflection-based DI
container := dig.New()
container.Provide(config.Load)
container.Provide(database.Open)
container.Provide(postgres.NewUserRepository)
container.Provide(service.NewUserService)
container.Invoke(func(svc *service.UserService) {
    // svc is fully constructed with all deps injected
    startServer(svc)
})

Trade-offs: Manual wiring is the most debuggable (stack traces show actual constructor calls). Wire generates readable code at compile time (fails fast, zero runtime overhead). Dig is most concise but uses reflection (runtime errors, harder to trace). The Go community generally prefers manual or Wire over Dig for production services.

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What is the main advantage of Wire (google/wire) over runtime DI frameworks like Dig?Wire requires less boilerplate code

✗ Try again.

Wire generates Go code at compile time — dependency mismatches are compile errors, not runtime panics; the generated code is readable and has zero reflection overhead

✓ Correct! Well done.

Wire works with any interface automatically

✗ Try again.

Wire supports circular dependencies that Dig cannot

✗ Try again.

When does manual dependency injection in main() become problematic?It always causes issues — frameworks are always preferred

✗ Try again.

When the service grows to 20+ dependencies with complex lifecycle management — main() becomes hard to read and errors like missing dependencies are caught only at runtime

✓ Correct! Well done.

When the service uses gRPC instead of REST

✗ Try again.

Manual DI does not support interface-based injection

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Golang / GoLang System Architecture and Testing Interview Questions

How do you manage dependency injection at scale in a large Go service — wire, dig, or manual?

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