使い方
- インストールコマンドをコピーし、自分の環境へ導入する前にソースを確認します。
- 必要なツール、認証情報、対応環境を原文で確認します。
- 入力と成果物を指定し、出力を資料と照合します。
npx skills add https://github.com/eduardo-sl/go-agent-skills --skill go-design-patterns開始前の確認
- 導入にはモデル契約、API枠、ファイルへのアクセス許可は含まれません。
- スター数や導入数は活動の指標であり、独立した品質・安全性試験ではありません。
見出し、例、コード、表、リンク、参照画像を含む原文を表示しています。
Go Design Patterns
Go favors composition over inheritance and simplicity over abstraction. These patterns are idiomatic Go — not Java patterns ported to Go.
Detailed reference material, loaded on demand:
references/creation-patterns.md— functional options (full example),
options vs config struct, constructors, factory.
references/behavioral-patterns.md— strategy, middleware/decorator,
result type, defer cleanup, sentinel vs zero values.
Read a reference file only when the summary below is not enough.
Pattern Selection
| Need | Pattern | Reference |
|---|---|---|
| Constructor with many optional settings | Functional options | creation-patterns.md |
| Config loaded from file/env, mostly required fields | Config struct | creation-patterns.md |
| Enforce invariants at creation | Constructor returning error | creation-patterns.md |
| Pick implementation from runtime config | Factory returning interface | creation-patterns.md |
| Swap simple behavior at runtime | Strategy via function type | behavioral-patterns.md |
| Swap complex behavior at runtime | Strategy via interface | behavioral-patterns.md |
| Wrap cross-cutting concerns (log, cache, metrics) | Middleware / decorator | behavioral-patterns.md |
| Value-or-error in concurrent pipelines | Result[T] struct | behavioral-patterns.md |
1. Functional Options (essentials)
type Option func(*Server)
func WithAddr(addr string) Option {
return func(s *Server) { s.addr = addr }
}
func NewServer(opts ...Option) *Server {
s := &Server{
addr: ":8080", // sensible defaults first
readTimeout: 5 * time.Second,
logger: slog.Default(),
}
for _, opt := range opts {
opt(s)
}
return s
}
srv := NewServer(WithAddr(":9090"))Use when: many optional parameters with sensible defaults, API evolves over time (new options don't break callers), options need validation. Use a plain config struct instead when most fields are required or the configuration is deserialized from file/env.
2. Constructor Rules
- Every exported type with invariants needs a constructor.
- Validate required dependencies; return an error, don't panic:
// ✅ Good — constructor enforces invariants
func NewUserService(repo UserRepository, logger *slog.Logger) (*UserService, error) {
if repo == nil {
return nil, errors.New("user service: nil repository")
}
return &UserService{repo: repo, logger: logger}, nil
}
// ❌ Bad — struct literal with no validation
svc := &UserService{} // nil dependencies → panic at runtime3. Factory
Return the interface, not a concrete type. The factory is the only place that knows about concrete implementations:
func NewStore(cfg Config) (Store, error) {
switch cfg.StoreType {
case "redis":
return newRedisStore(cfg.RedisAddr)
case "memory":
return newMemoryStore(), nil
default:
return nil, fmt.Errorf("unknown store type: %s", cfg.StoreType)
}
}4. Middleware Chain
The standard HTTP composition pattern:
type Middleware func(http.Handler) http.Handler
func Chain(handler http.Handler, middlewares ...Middleware) http.Handler {
for i := len(middlewares) - 1; i >= 0; i-- {
handler = middlewares[i](handler)
}
return handler
}
handler := Chain(appHandler, Recoverer, RequestID, Logger, Auth)The same shape works for any interface: stack decorators as cache → logging → metrics → actual repo (see references/behavioral-patterns.md).
5. Zero Values First
Prefer types whose zero value is useful (sync.Mutex, bytes.Buffer, nil slices). Reach for sentinel wrappers or pointers only when the zero value is ambiguous as an input (nil *float64 = "not configured").
Anti-Patterns to Avoid
// ❌ God interface — too many methods
type Service interface {
GetUser(ctx context.Context, id string) (*User, error)
CreateUser(ctx context.Context, u *User) error
DeleteUser(ctx context.Context, id string) error
ListOrders(ctx context.Context, userID string) ([]Order, error)
// 20 more methods...
}
// → Split into focused interfaces: UserReader, UserWriter, OrderLister
// ❌ Premature abstraction — interface for one implementation
type UserCache interface {
Get(key string) (*User, bool)
Set(key string, user *User)
}
// If there's only ever one implementation, use the concrete type.
// Extract an interface when a second consumer or implementation appears.
// ❌ Java-style inheritance simulation
type BaseService struct{ /* ... */ }
type UserService struct{ BaseService } // embedding is NOT inheritance
// → Use composition: UserService has a dependency, not a parent.Verification Checklist
- Functional options used for types with optional configuration
- Constructors validate required dependencies and return errors
- Factory functions return interfaces, not concrete types
- No god interfaces — each interface has 1-3 methods
- Middleware follows
func(http.Handler) http.Handlersignature - Decorators wrap interfaces, not concrete types
deferused for all resource cleanup (files, connections, locks)- Zero values are meaningful — no unnecessary initialization
- No premature abstractions — interfaces extracted only when needed
- Composition used instead of embedding for code reuse
