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Comprehensive guide for dependency injection (DI) in Golang. Covers why DI matters (testability, loose coupling, separation of concerns, lifecycle management), manual constructor injection, and DI lib
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Comprehensive guide for dependency injection (DI) in Golang. Covers why DI matters (testability, loose coupling, separation of concerns, lifecycle management), manual constructor injection, and DI library comparison (google/wire, uber-go/dig, uber-go/fx, samber/do). Use this skill when designing service architecture, setting up dependency injection, refactoring tightly coupled code, managing singletons or service factories, or when the user asks about inversion of control, service containers, or wiring dependencies in Go. For a specific DI library, → See `samber/cc-skills-golang@golang-google-wire`, `samber/cc-skills-golang@golang-uber-dig`, `samber/cc-skills-golang@golang-uber-fx`, or `samber/cc-skills-golang@golang-samber-do` skills.
Comprehensive guide for dependency injection (DI) in Golang. Covers why DI matters (testability, loose coupling, separation of concerns, lifecycle management), manual constructor injection, and DI library comparison (google/wire, uber-go/dig, uber-go/fx, samber/do). Use this skill when designing service architecture, setting up dependency injection, refactoring tightly coupled code, managing singletons or service factories, or when the user asks about inversion of control, service containers, or wiring dependencies in Go. For a specific DI library, → See `samber/cc-skills-golang@golang-google-wire`, `samber/cc-skills-golang@golang-uber-dig`, `samber/cc-skills-golang@golang-uber-fx`, or `samber/cc-skills-golang@golang-samber-do` skills.
name: golang-dependency-injection
description: "Comprehensive guide for dependency injection (DI) in Golang. Covers why DI matters (testability, loose coupling, separation of concerns, lifecycle management), manual constructor injection, and DI library comparison (google/wire, uber-go/dig, uber-go/fx, samber/do). Use this skill when designing service architecture, setting up dependency injection, refactoring tightly coupled code, managing singletons or service factories, or when the user asks about inversion of control, service containers, or wiring dependencies in Go. For a specific DI library, → See samber/cc-skills-golang@golang-google-wire, samber/cc-skills-golang@golang-uber-dig, samber/cc-skills-golang@golang-uber-fx, or samber/cc-skills-golang@golang-samber-do skills."
user-invocable: true
license: MIT
compatibility: Designed for Claude Code, Codex or similar harness, and for projects using Golang.
metadata:
author: samber
version: "1.3.1"
openclaw:
emoji: "🔌"
homepage: https://github.com/samber/cc-skills-golang
requires:
bins:
- go
install: []
allowed-tools: Read Edit Write Glob Grep Bash(go:) Bash(golangci-lint:) Bash(git:*) Agent WebFetch mcp__context7__resolve-library-id mcp__context7__query-docs AskUserQuestion
paths:
Persona: You are a Go software architect. You guide teams toward testable, loosely coupled designs — you choose the simplest DI approach that solves the problem, and you never over-engineer.
Orchestration mode: Fan out the three sub-agents described in Refactor mode (global/init discovery, concrete-dependency mapping, service-locator detection) when refactoring a large coupled codebase toward dependency injection, and consolidate into one migration plan. On Claude Code, use ultracode to opt into multi-agent orchestration explicitly.
Modes:
init() service setup, Agent 2 maps concrete type dependencies that should become interfaces, Agent 3 locates service-locator anti-patterns (container passed as argument) — then consolidate findings and propose a migration plan.Community default. A company skill that explicitly supersedes
samber/cc-skills-golang@golang-dependency-injectionskill takes precedence.
Dependency injection (DI) means passing dependencies to a component rather than having it create or find them. In Go, this is how you build testable, loosely coupled applications — your services declare what they need, and the caller (or container) provides it.
This skill is not exhaustive. When using a DI library (google/wire, uber-go/dig, uber-go/fx, samber/do), refer to the library's official documentation and code examples for current API signatures.
For interface-based design foundations (accept interfaces, return structs), see the samber/cc-skills-golang@golang-structs-interfaces skill.
init() for service setupmain() or app startup) — NEVER pass the container as a dependency| Problem without DI | How DI solves it |
|---|---|
| Functions create their own dependencies | Dependencies are injected — swap implementations freely |
| Testing requires real databases, APIs | Pass mock implementations in tests |
| Changing one component breaks others | Loose coupling via interfaces — components don't know each other's internals |
| Services initialized everywhere | Centralized container manages lifecycle (singleton, factory, lazy) |
| All services loaded at startup | Lazy loading — services created only when first requested |
Global state and init() functions | Explicit wiring at startup — predictable, debuggable |
DI shines in applications with many interconnected services — HTTP servers, microservices, CLI tools with plugins. For a small script with 2-3 functions, manual wiring is fine. Don't over-engineer.
For small projects, pass dependencies through constructors. See Manual DI examples for a complete application example.
// ✓ Good — explicit dependencies, testable
type UserService struct {
db UserStore
mailer Mailer
logger *slog.Logger
}
func NewUserService(db UserStore, mailer Mailer, logger *slog.Logger) *UserService {
return &UserService{db: db, mailer: mailer, logger: logger}
}
// main.go — manual wiring
func main() {
logger := slog.Default()
db := postgres.NewUserStore(connStr)
mailer := smtp.NewMailer(smtpAddr)
userSvc := NewUserService(db, mailer, logger)
orderSvc := NewOrderService(db, logger)
api := NewAPI(userSvc, orderSvc, logger)
api.ListenAndServe(":8080")
}
// ✗ Bad — hardcoded dependencies, untestable
type UserService struct {
db *sql.DB
}
func NewUserService() *UserService {
db, _ := sql.Open("postgres", os.Getenv("DATABASE_URL")) // hidden dependency
return &UserService{db: db}
}
Manual DI breaks down when:
Go has three main approaches to DI libraries:
| Criteria | Manual | google/wire | uber-go/dig + fx | samber/do |
|---|---|---|---|---|
| Project size | Small (< 10 services) | Medium-Large | Large | Any size |
| Type safety | Compile-time | Compile-time (codegen) | Runtime (reflection) | Compile-time (generics) |
| Code generation | None | Required (wire_gen.go) | None | None |
| Reflection | None | None | Yes | None |
| API style | N/A | Provider sets + build tags | Struct tags + decorators | Simple, generic functions |
| Lazy loading | Manual | N/A (all eager) | Built-in (fx) | Built-in |
| Singletons | Manual | Built-in | Built-in | Built-in |
| Transient/factory | Manual | Manual | Built-in | Built-in |
| Scopes/modules | Manual | Provider sets | Module system (fx) | Built-in (hierarchical) |
| Health checks | Manual | Manual | Manual | Built-in interface |
| Graceful shutdown | Manual | Manual | Built-in (fx) | Built-in interface |
| Container cloning | N/A | N/A | N/A | Built-in |
| Debugging | Print statements | Compile errors | fx.Visualize() | ExplainInjector(), web interface |
| Go version | Any | Any | Any | 1.18+ (generics) |
| Learning curve | None | Medium | High |
The same graph — Config -> Database -> UserStore -> UserService -> API — wired by hand and by a container. The contrast is what the wiring code encodes: an ordered call sequence you maintain, versus a set of providers the container orders for you.
// Manual — you own the order; adding a dependency means editing every call site downstream
cfg := NewConfig()
db := NewDatabase(cfg)
store := NewUserStore(db)
svc := NewUserService(store)
api := NewAPI(svc)
api.Run()
// No shutdown hooks, health checks, or lazy loading — add them yourself
// Container (samber/do) — order is derived from the constructor signatures
i := do.New()
do.Provide(i, NewConfig)
do.Provide(i, NewDatabase)
do.Provide(i, NewUserStore)
do.Provide(i, NewUserService)
api := do.MustInvoke[*API](i)
api.Run()
defer i.Shutdown() // shutdown and health checks come from the container
google/wire and uber-go/fx express the same graph differently: wire generates the manual sequence above at build time from a wire.Build provider list (cleanup via func() returned by providers, no lifecycle hooks), while fx registers providers with fx.Provide and resolves them by reflection at runtime with OnStart/OnStop hooks. Full wiring examples for each: google/wire, uber-go/dig + fx, samber/do.
DI makes testing straightforward — inject mocks instead of real implementations:
// Define a mock
type MockUserStore struct {
users map[string]*User
}
func (m *MockUserStore) FindByID(ctx context.Context, id string) (*User, error) {
u, ok := m.users[id]
if !ok {
return nil, ErrNotFound
}
return u, nil
}
// Test with manual injection
func TestUserService_GetUser(t *testing.T) {
mock := &MockUserStore{
users: map[string]*User{"1": {ID: "1", Name: "Alice"}},
}
svc := NewUserService(mock, nil, slog.Default())
user, err := svc.GetUser(context.Background(), "1")
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
if user.Name != "Alice" {
t.Errorf("got %q, want %q", user.Name, "Alice")
}
}
Container cloning creates an isolated copy where you override only the services you need to mock:
func TestUserService_WithDo(t *testing.T) {
// Create a test injector with mock implementation
testInjector := do.New()
// Provide the mock UserStore interface
do.OverrideValue[UserStore](testInjector, &MockUserStore{
users: map[string]*User{"1": {ID: "1", Name: "Alice"}},
})
// Provide other real services as needed
do.Provide[*slog.Logger](testInjector, func(i *do.Injector) (*slog.Logger, error) {
return slog.Default(), nil
})
svc := do.MustInvoke[*UserService](testInjector)
user, err := svc.GetUser(context.Background(), "1")
// ... assertions
}
This is particularly useful for integration tests where you want most services to be real but need to mock a specific boundary (database, external API, mailer).
| Signal | Action |
|---|---|
| < 10 services, simple dependencies | Stay with manual constructor injection |
| 10-20 services, some cross-cutting concerns | Consider a DI library |
| 20+ services, lifecycle management needed | Strongly recommended |
| Need health checks, graceful shutdown | Use a library with built-in lifecycle support |
| Team unfamiliar with DI concepts | Start manual, migrate incrementally |
| Mistake | Fix |
|---|---|
| Global variables as dependencies | Pass through constructors or DI container |
init() for service setup | Explicit initialization in main() or container |
| Depending on concrete types | Accept interfaces at consumption boundaries |
| Passing the container everywhere (service locator) | Inject specific dependencies, not the container |
| Deep dependency chains (A->B->C->D->E) | Flatten — most services should depend on repositories and config directly |
| Creating a new container per request | One container per application; use scopes for request-level isolation |
samber/cc-skills-golang@golang-samber-do skill for detailed samber/do usage patternssamber/cc-skills-golang@golang-structs-interfaces skill for interface design and compositionsamber/cc-skills-golang@golang-testing skill for testing with dependency injectionsamber/cc-skills-golang@golang-project-layout skill for DI initialization placement| Low |