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This skill helps you apply idiomatic Go patterns to write simpler, safer, and more maintainable code.
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---
name: golang-patterns
description: Idiomatic Go patterns, best practices, and conventions for building robust, efficient, and maintainable Go applications.
---
# Go Development Patterns
Idiomatic Go patterns and best practices for building robust, efficient, and maintainable applications.
## When to Activate
- Writing new Go code
- Reviewing Go code
- Refactoring existing Go code
- Designing Go packages/modules
## Core Principles
### 1. Simplicity and Clarity
Go favors simplicity over cleverness. Code should be obvious and easy to read.
```go
// Good: Clear and direct
func GetUser(id string) (*User, error) {
user, err := db.FindUser(id)
if err != nil {
return nil, fmt.Errorf("get user %s: %w", id, err)
}
return user, nil
}
// Bad: Overly clever
func GetUser(id string) (*User, error) {
return func() (*User, error) {
if u, e := db.FindUser(id); e == nil {
return u, nil
} else {
return nil, e
}
}()
}
```
### 2. Make the Zero Value Useful
Design types so their zero value is immediately usable without initialization.
```go
// Good: Zero value is useful
type Counter struct {
mu sync.Mutex
count int // zero value is 0, ready to use
}
func (c *Counter) Inc() {
c.mu.Lock()
c.count++
c.mu.Unlock()
}
// Good: bytes.Buffer works with zero value
var buf bytes.Buffer
buf.WriteString("hello")
// Bad: Requires initialization
type BadCounter struct {
counts map[string]int // nil map will panic
}
```
### 3. Accept Interfaces, Return Structs
Functions should accept interface parameters and return concrete types.
```go
// Good: Accepts interface, returns concrete type
func ProcessData(r io.Reader) (*Result, error) {
data, err := io.ReadAll(r)
if err != nil {
return nil, err
}
return &Result{Data: data}, nil
}
// Bad: Returns interface (hides implementation details unnecessarily)
func ProcessData(r io.Reader) (io.Reader, error) {
// ...
}
```
## Error Handling Patterns
### Error Wrapping with Context
```go
// Good: Wrap errors with context
func LoadConfig(path string) (*Config, error) {
data, err := os.ReadFile(path)
if err != nil {
return nil, fmt.Errorf("load config %s: %w", path, err)
}
var cfg Config
if err := json.Unmarshal(data, &cfg); err != nil {
return nil, fmt.Errorf("parse config %s: %w", path, err)
}
return &cfg, nil
}
```
### Custom Error Types
```go
// Define domain-specific errors
type ValidationError struct {
Field string
Message string
}
func (e *ValidationError) Error() string {
return fmt.Sprintf("validation failed on %s: %s", e.Field, e.Message)
}
// Sentinel errors for common cases
var (
ErrNotFound = errors.New("resource not found")
ErrUnauthorized = errors.New("unauthorized")
ErrInvalidInput = errors.New("invalid input")
)
```
### Error Checking with errors.Is and errors.As
```go
func HandleError(err error) {
// Check for specific error
if errors.Is(err, sql.ErrNoRows) {
log.Println("No records found")
return
}
// Check for error type
var validationErr *ValidationError
if errors.As(err, &validationErr) {
log.Printf("Validation error on field %s: %s",
validationErr.Field, validationErr.Message)
return
}
// Unknown error
log.Printf("Unexpected error: %v", err)
}
```
### Never Ignore Errors
```go
// Bad: Ignoring error with blank identifier
result, _ := doSomething()
// Good: Handle or explicitly document why it's safe to ignore
result, err := doSomething()
if err != nil {
return err
}
// Acceptable: When error truly doesn't matter (rare)
_ = writer.Close() // Best-effort cleanup, error logged elsewhere
```
## Concurrency Patterns
### Worker Pool
```go
func WorkerPool(jobs <-chan Job, results chan<- Result, numWorkers int) {
var wg sync.WaitGroup
for i := 0; i < numWorkers; i++ {
wg.Add(1)
go func() {
defer wg.Done()
for job := range jobs {
results <- process(job)
}
}()
}
wg.Wait()
close(results)
}
```
### Context for Cancellation and Timeouts
```go
func FetchWithTimeout(ctx context.Context, url string) ([]byte, error) {
ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
defer cancel()
req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
if err != nil {
return nil, fmt.Errorf("create request: %w", err)
}
resp, err := http.DefaultClient.Do(req)
if err != nil {
return nil, fmt.Errorf("fetch %s: %w", url, err)
}
defer resp.Body.Close()
return io.ReadAll(resp.Body)
}
```
### Graceful Shutdown
```go
func GracefulShutdown(server *http.Server) {
quit := make(chan os.Signal, 1)
signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
<-quit
log.Println("Shutting down server...")
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
if err := server.Shutdown(ctx); err != nil {
log.Fatalf("Server forced to shutdown: %v", err)
}
log.Println("Server exited")
}
```
### errgroup for Coordinated Goroutines
```go
import "golang.org/x/sync/errgroup"
func FetchAll(ctx context.Context, urls []string) ([][]byte, error) {
g, ctx := errgroup.WithContext(ctx)
results := make([][]byte, len(urls))
for i, url := range urls {
i, url := i, url // Capture loop variables
g.Go(func() error {
data, err := FetchWithTimeout(ctx, url)
if err != nil {
return err
}
results[i] = data
return nil
})
}
if err := g.Wait(); err != nil {
return nil, err
}
return results, nil
}
```
### Avoiding Goroutine Leaks
```go
// Bad: Goroutine leak if context is cancelled
func leakyFetch(ctx context.Context, url string) <-chan []byte {
ch := make(chan []byte)
go func() {
data, _ := fetch(url)
ch <- data // Blocks forever if no receiver
}()
return ch
}
// Good: Properly handles cancellation
func safeFetch(ctx context.Context, url string) <-chan []byte {
ch := make(chan []byte, 1) // Buffered channel
go func() {
data, err := fetch(url)
if err != nil {
return
}
select {
case ch <- data:
case <-ctx.Done():
}
}()
return ch
}
```
## Interface Design
### Small, Focused Interfaces
```go
// Good: Single-method interfaces
type Reader interface {
Read(p []byte) (n int, err error)
}
type Writer interface {
Write(p []byte) (n int, err error)
}
type Closer interface {
Close() error
}
// Compose interfaces as needed
type ReadWriteCloser interface {
Reader
Writer
Closer
}
```
### Define Interfaces Where They're Used
```go
// In the consumer package, not the provider
package service
// UserStore defines what this service needs
type UserStore interface {
GetUser(id string) (*User, error)
SaveUser(user *User) error
}
type Service struct {
store UserStore
}
// Concrete implementation can be in another package
// It doesn't need to know about this interface
```
### Optional Behavior with Type Assertions
```go
type Flusher interface {
Flush() error
}
func WriteAndFlush(w io.Writer, data []byte) error {
if _, err := w.Write(data); err != nil {
return err
}
// Flush if supported
if f, ok := w.(Flusher); ok {
return f.Flush()
}
return nil
}
```
## Package Organization
### Standard Project Layout
```text
myproject/
├── cmd/
│ └── myapp/
│ └── main.go # Entry point
├── internal/
│ ├── handler/ # HTTP handlers
│ ├── service/ # Business logic
│ ├── repository/ # Data access
│ └── config/ # Configuration
├── pkg/
│ └── client/ # Public API client
├── api/
│ └── v1/ # API definitions (proto, OpenAPI)
├── testdata/ # Test fixtures
├── go.mod
├── go.sum
└── Makefile
```
### Package Naming
```go
// Good: Short, lowercase, no underscores
package http
package json
package user
// Bad: Verbose, mixed case, or redundant
package httpHandler
package json_parser
package userService // Redundant 'Service' suffix
```
### Avoid Package-Level State
```go
// Bad: Global mutable state
var db *sql.DB
func init() {
db, _ = sql.Open("postgres", os.Getenv("DATABASE_URL"))
}
// Good: Dependency injection
type Server struct {
db *sql.DB
}
func NewServer(db *sql.DB) *Server {
return &Server{db: db}
}
```
## Struct Design
### Functional Options Pattern
```go
type Server struct {
addr string
timeout time.Duration
logger *log.Logger
}
type Option func(*Server)
func WithTimeout(d time.Duration) Option {
return func(s *Server) {
s.timeout = d
}
}
func WithLogger(l *log.Logger) Option {
return func(s *Server) {
s.logger = l
}
}
func NewServer(addr string, opts ...Option) *Server {
s := &Server{
addr: addr,
timeout: 30 * time.Second, // default
logger: log.Default(), // default
}
for _, opt := range opts {
opt(s)
}
return s
}
// Usage
server := NewServer(":8080",
WithTimeout(60*time.Second),
WithLogger(customLogger),
)
```
### Embedding for Composition
```go
type Logger struct {
prefix string
}
func (l *Logger) Log(msg string) {
fmt.Printf("[%s] %s\n", l.prefix, msg)
}
type Server struct {
*Logger // Embedding - Server gets Log method
addr string
}
func NewServer(addr string) *Server {
return &Server{
Logger: &Logger{prefix: "SERVER"},
addr: addr,
}
}
// Usage
s := NewServer(":8080")
s.Log("Starting...") // Calls embedded Logger.Log
```
## Memory and Performance
### Preallocate Slices When Size is Known
```go
// Bad: Grows slice multiple times
func processItems(items []Item) []Result {
var results []Result
for _, item := range items {
results = append(results, process(item))
}
return results
}
// Good: Single allocation
func processItems(items []Item) []Result {
results := make([]Result, 0, len(items))
for _, item := range items {
results = append(results, process(item))
}
return results
}
```
### Use sync.Pool for Frequent Allocations
```go
var bufferPool = sync.Pool{
New: func() interface{} {
return new(bytes.Buffer)
},
}
func ProcessRequest(data []byte) []byte {
buf := bufferPool.Get().(*bytes.Buffer)
defer func() {
buf.Reset()
bufferPool.Put(buf)
}()
buf.Write(data)
// Process...
return buf.Bytes()
}
```
### Avoid String Concatenation in Loops
```go
// Bad: Creates many string allocations
func join(parts []string) string {
var result string
for _, p := range parts {
result += p + ","
}
return result
}
// Good: Single allocation with strings.Builder
func join(parts []string) string {
var sb strings.Builder
for i, p := range parts {
if i > 0 {
sb.WriteString(",")
}
sb.WriteString(p)
}
return sb.String()
}
// Best: Use standard library
func join(parts []string) string {
return strings.Join(parts, ",")
}
```
## Go Tooling Integration
### Essential Commands
```bash
# Build and run
go build ./...
go run ./cmd/myapp
# Testing
go test ./...
go test -race ./...
go test -cover ./...
# Static analysis
go vet ./...
staticcheck ./...
golangci-lint run
# Module management
go mod tidy
go mod verify
# Formatting
gofmt -w .
goimports -w .
```
### Recommended Linter Configuration (.golangci.yml)
```yaml
linters:
enable:
- errcheck
- gosimple
- govet
- ineffassign
- staticcheck
- unused
- gofmt
- goimports
- misspell
- unconvert
- unparam
linters-settings:
errcheck:
check-type-assertions: true
govet:
check-shadowing: true
issues:
exclude-use-default: false
```
## Quick Reference: Go Idioms
| Idiom | Description |
|-------|-------------|
| Accept interfaces, return structs | Functions accept interface params, return concrete types |
| Errors are values | Treat errors as first-class values, not exceptions |
| Don't communicate by sharing memory | Use channels for coordination between goroutines |
| Make the zero value useful | Types should work without explicit initialization |
| A little copying is better than a little dependency | Avoid unnecessary external dependencies |
| Clear is better than clever | Prioritize readability over cleverness |
| gofmt is no one's favorite but everyone's friend | Always format with gofmt/goimports |
| Return early | Handle errors first, keep happy path unindented |
## Anti-Patterns to Avoid
```go
// Bad: Naked returns in long functions
func process() (result int, err error) {
// ... 50 lines ...
return // What is being returned?
}
// Bad: Using panic for control flow
func GetUser(id string) *User {
user, err := db.Find(id)
if err != nil {
panic(err) // Don't do this
}
return user
}
// Bad: Passing context in struct
type Request struct {
ctx context.Context // Context should be first param
ID string
}
// Good: Context as first parameter
func ProcessRequest(ctx context.Context, id string) error {
// ...
}
// Bad: Mixing value and pointer receivers
type Counter struct{ n int }
func (c Counter) Value() int { return c.n } // Value receiver
func (c *Counter) Increment() { c.n++ } // Pointer receiver
// Pick one style and be consistent
```
**Remember**: Go code should be boring in the best way - predictable, consistent, and easy to understand. When in doubt, keep it simple.
This skill codifies idiomatic Go patterns, best practices, and conventions to help you build robust, efficient, and maintainable Go applications. It focuses on readability, safe concurrency, error handling, package and API design, and performance optimizations. Use it as a practical checklist during development, reviews, and refactors.
The skill inspects common Go design areas and recommends concrete patterns: making zero values useful, accepting interfaces and returning concrete types, clear error wrapping, and safe concurrency constructs. It highlights anti-patterns, suggests tooling and linter settings, and provides concise code idioms and examples you can apply directly to functions, packages, and system-level design. Outputs are actionable guidelines aimed at reducing bugs and improving long-term maintainability.
Should I always return concrete types instead of interfaces?
Prefer returning concrete types to keep callers simple; accept interfaces for inputs so callers can pass flexible implementations.
When is it acceptable to ignore an error?
Only ignore errors when it genuinely has no observable effect (rare). Otherwise handle or explicitly document why it is safe to ignore.