Golang Patterns

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.

// 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.

// 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.

// 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

Use fmt.Errorf with %w to wrap errors and preserve the error chain:

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
}

For custom error types and error checking patterns, see references/code-examples.md.

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)
}

For context cancellation, graceful shutdown, errgroup, and goroutine leak prevention patterns, see references/code-examples.md.

Context as First Parameter

Always pass context.Context as the first parameter of a function:

func ProcessRequest(ctx context.Context, id string) error {
    // Use ctx for timeouts, cancellation, and request-scoped values
    select {
    case <-ctx.Done():
        return ctx.Err()
    default:
        // Process...
    }
}

## Interface Design

### Small, Focused Interfaces

```go
// Single-method interfaces compose cleanly
type Reader interface {
    Read(p []byte) (n int, err error)
}

type Writer interface {
    Write(p []byte) (n int, err error)
}

// Compose interfaces as needed
type ReadWriteCloser interface {
    Reader
    Writer
    Closer
}

For patterns on defining interfaces where they're used and optional behavior with type assertions, see references/code-examples.md.

Package Organization

Standard Project Layout

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

// 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

// 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

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 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
}

For embedding patterns, see references/code-examples.md.

Memory and Performance

Preallocate Slices When Size is Known

// Preferred: Single allocation
func processItems(items []Item) []Result {
    results := make([]Result, 0, len(items))
    for _, item := range items {
        results = append(results, process(item))
    }
    return results
}

For sync.Pool and string concatenation patterns, see references/code-examples.md.

Go Tooling Integration

Essential Commands

# 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)

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

Anti-Patterns to Avoid

Avoid naked returns in long functions — they obscure what is being returned. Use explicit returns:

// Clearer: Explicit returns
func process() (int, error) {
    // ... logic ...
    return result, nil
}

Avoid using panic for control flow. Return errors instead:

// Prefer: Return error
func GetUser(id string) (*User, error) {
    user, err := db.Find(id)
    if err != nil {
        return nil, err
    }
    return user, nil
}

Avoid mixing value and pointer receivers on the same type. Pick one style and be consistent.

Prefer context as the first parameter, not inside struct fields.

Go Version Notes (June 2026)

Current: Go 1.26 (Feb 2026). Key recent additions:

• Go 1.26: Self-referential generics, new with expressions, experimental runtime/secret
• Go 1.25: Removed "core types" concept, experimental encoding/json/v2, PGO stabilized
• Go 1.24: Generic type aliases, os.Root for directory-limited filesystem, Swiss Tables for maps