What are error handling best practices in Go?

Question

Accepted Answer

Best practices for **error handling** in Go.

```go
// 1. Don't ignore errors
// Bad:
result, _ := doSomething()

// Good:
result, err := doSomething()
if err != nil {
    return fmt.Errorf("doSomething: %w", err)
}

// 2. Wrap errors with context
func ProcessUser(id int) error {
    user, err := GetUser(id)
    if err != nil {
        return fmt.Errorf("ProcessUser: GetUser(%d): %w", id, err)
    }
    return nil
}

// 3. Use sentinel errors for checking
var ErrNotFound = errors.New("not found")

if errors.Is(err, ErrNotFound) {
    http.Error(w, "Not found", 404)
}

// 4. Custom errors for additional information
type ValidationError struct {
    Field   string
    Message string
}

func (e *ValidationError) Error() string {
    return fmt.Sprintf("%s: %s", e.Field, e.Message)
}

// 5. Error joining (Go 1.20+)
errs := errors.Join(err1, err2, err3)
if errs != nil {
    log.Println("Multiple errors:", errs)
}

// 6. errorlint for checking
// Don't use: err == SomeError
// Use: errors.Is(err, SomeError)

// 7. errgroup for parallel operations
g, ctx := errgroup.WithContext(context.Background())
for _, url := range urls {
    url := url
    g.Go(func() error {
        return fetch(ctx, url)
    })
}
if err := g.Wait(); err != nil {
    return fmt.Errorf("fetch all: %w", err)
}
```

**Golden rules:**
- Always check errors.
- Wrap with context.
- Don't use panic for errors.
- errors.Is/errors.As instead of ==.

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