Go 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.

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
}

// 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

// 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")

3. Accept Interfaces, Return Structs

// 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
}

Error Handling Patterns

Error Wrapping 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

// 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")
)

Concurrency Patterns

Worker Pool

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

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

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")
}

Interface Design

Small, Focused Interfaces

// 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
}

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
Clear is better than clever	Prioritize readability over cleverness
Return early	Handle errors first, keep happy path unindented

Go code should be boring in the best way - predictable, consistent, and easy to understand. When in doubt, keep it simple.

Overview

Core Skills

Development Patterns

Language-Specific Skills

Advanced Skills

When to Activate

Core Principles

1. Simplicity and Clarity

2. Make the Zero Value Useful

3. Accept Interfaces, Return Structs

Error Handling Patterns

Error Wrapping with Context

Custom Error Types

Concurrency Patterns

Worker Pool

Context for Cancellation and Timeouts

Graceful Shutdown

Interface Design

Small, Focused Interfaces

Quick Reference: Go Idioms

​When to Activate

​Core Principles

​1. Simplicity and Clarity

​2. Make the Zero Value Useful

​3. Accept Interfaces, Return Structs

​Error Handling Patterns

​Error Wrapping with Context

​Custom Error Types

​Concurrency Patterns

​Worker Pool

​Context for Cancellation and Timeouts

​Graceful Shutdown

​Interface Design

​Small, Focused Interfaces

​Quick Reference: Go Idioms

When to Activate

Core Principles

1. Simplicity and Clarity

2. Make the Zero Value Useful

3. Accept Interfaces, Return Structs

Error Handling Patterns

Error Wrapping with Context

Custom Error Types

Concurrency Patterns

Worker Pool

Context for Cancellation and Timeouts

Graceful Shutdown

Interface Design

Small, Focused Interfaces

Quick Reference: Go Idioms