Matter AI | Code Reviewer Documentation

Go Anti-Patterns Overview

Not Handling Errors Properly

// Anti-pattern: Ignoring errors
func readFile(path string) []byte {
    data, _ := ioutil.ReadFile(path) // Ignoring error
    return data
}

// Better approach: Handle errors
func readFile(path string) ([]byte, error) {
    data, err := ioutil.ReadFile(path)
    if err != nil {
        return nil, fmt.Errorf("failed to read file %s: %w", path, err)
    }
    return data, nil
}

Go’s explicit error handling is a feature, not a burden. Always check and handle errors appropriately, and consider using the %w verb to wrap errors for better context.

Using Empty Interface (interface{}) Excessively

// Anti-pattern: Overusing empty interface
func processData(data interface{}) interface{} {
    // Type assertions everywhere
    switch v := data.(type) {
    case string:
        return v + " processed"
    case int:
        return v * 2
    default:
        return nil
    }
}

// Better approach: Use specific interfaces
type Processor interface {
    Process() string
}

type StringData string
func (s StringData) Process() string {
    return string(s) + " processed"
}

type IntData int
func (i IntData) Process() string {
    return strconv.Itoa(int(i) * 2)
}

func processData(data Processor) string {
    return data.Process()
}

The empty interface (interface{}) bypasses Go’s type system. Use specific interfaces that define the behavior you need instead.

Not Using Context for Cancellation

// Anti-pattern: Not using context for cancellation
func fetchData(url string) ([]byte, error) {
    resp, err := http.Get(url)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()
    return ioutil.ReadAll(resp.Body)
}

// Better approach: Use context for cancellation
func fetchData(ctx context.Context, url string) ([]byte, error) {
    req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
    if err != nil {
        return nil, err
    }
    
    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()
    
    return ioutil.ReadAll(resp.Body)
}

Use context.Context for cancellation, timeouts, and passing request-scoped values. This allows callers to cancel long-running operations.

Returning Naked Returns

// Anti-pattern: Using naked returns
func divide(a, b int) (result int, err error) {
    if b == 0 {
        err = errors.New("division by zero")
        return
    }
    result = a / b
    return
}

// Better approach: Explicit returns
func divide(a, b int) (int, error) {
    if b == 0 {
        return 0, errors.New("division by zero")
    }
    return a / b, nil
}

Naked returns (returns without arguments) can make code harder to understand, especially in longer functions. Use explicit returns for clarity.

Using init() Functions Excessively

// Anti-pattern: Overusing init()
var db *sql.DB

func init() {
    var err error
    db, err = sql.Open("postgres", "connection-string")
    if err != nil {
        log.Fatal(err) // Program exits if DB connection fails
    }
}

// Better approach: Explicit initialization
func NewApp() (*App, error) {
    db, err := sql.Open("postgres", "connection-string")
    if err != nil {
        return nil, err
    }
    
    return &App{db: db}, nil
}

init() functions run before main() and can’t return errors. Use explicit initialization functions that can handle errors gracefully.

Not Using Proper Package Organization

// Anti-pattern: Poor package organization
// All code in one package
package main

// User-related code
type User struct { /* ... */ }
func CreateUser() { /* ... */ }

// Order-related code
type Order struct { /* ... */ }
func PlaceOrder() { /* ... */ }

// Better approach: Organize by domain
// user/user.go
package user

type User struct { /* ... */ }
func Create() { /* ... */ }

// order/order.go
package order

type Order struct { /* ... */ }
func Place() { /* ... */ }

Organize packages by domain, not by technical function. Each package should have a single, well-defined purpose.

Using Global Variables

// Anti-pattern: Using global variables
var (  
    db *sql.DB
    logger *log.Logger
    config Config
)

func GetUser(id string) (*User, error) {
    // Using global db
    return db.QueryUser(id)
}

// Better approach: Dependency injection
type UserService struct {
    db *sql.DB
    logger *log.Logger
    config Config
}

func NewUserService(db *sql.DB, logger *log.Logger, config Config) *UserService {
    return &UserService{db, logger, config}
}

func (s *UserService) GetUser(id string) (*User, error) {
    return s.db.QueryUser(id)
}

Global variables make testing difficult and create implicit dependencies. Use dependency injection to make dependencies explicit.

Not Using Interfaces for Testability

// Anti-pattern: Direct dependency on concrete types
type UserService struct {
    db *sql.DB
}

func (s *UserService) GetUser(id string) (*User, error) {
    // Direct dependency on sql.DB
    row := s.db.QueryRow("SELECT * FROM users WHERE id = $1", id)
    // ...
}

// Better approach: Depend on interfaces
type Database interface {
    QueryRow(query string, args ...interface{}) Row
}

type Row interface {
    Scan(dest ...interface{}) error
}

type UserService struct {
    db Database
}

func (s *UserService) GetUser(id string) (*User, error) {
    // Dependency on interface, not concrete type
    row := s.db.QueryRow("SELECT * FROM users WHERE id = $1", id)
    // ...
}

Depend on interfaces, not concrete implementations, to make your code more testable and flexible.

Using Pointers Unnecessarily

// Anti-pattern: Unnecessary pointers
func NewUser(name string, age int) *User {
    return &User{name, age}
}

func ProcessUser(user *User) {
    // No modification to user
    fmt.Println(user.name, user.age)
}

// Better approach: Use values for immutable data
func NewUser(name string, age int) User {
    return User{name, age}
}

func ProcessUser(user User) {
    // No modification needed, pass by value
    fmt.Println(user.name, user.age)
}

Only use pointers when you need to modify the data or when the struct is very large. For small, immutable data, use values.

Not Using defer for Cleanup

// Anti-pattern: Manual cleanup
func processFile(path string) error {
    f, err := os.Open(path)
    if err != nil {
        return err
    }
    
    // Process file...
    
    // What if there's an error here? The file won't be closed
    f.Close()
    return nil
}

// Better approach: Use defer for cleanup
func processFile(path string) error {
    f, err := os.Open(path)
    if err != nil {
        return err
    }
    defer f.Close() // Will be called even if the function returns early
    
    // Process file...
    
    return nil
}

Use defer for cleanup operations to ensure they happen even if the function returns early due to an error.

Not Using Structured Logging

// Anti-pattern: Unstructured logging
func processOrder(order Order) error {
    log.Printf("Processing order %s for customer %s", order.ID, order.CustomerID)
    // Process order...
    log.Printf("Order %s processed successfully", order.ID)
    return nil
}

// Better approach: Structured logging
func processOrder(order Order) error {
    logger := log.With(
        "order_id", order.ID,
        "customer_id", order.CustomerID,
    )
    
    logger.Info("Processing order")
    // Process order...
    logger.Info("Order processed successfully")
    return nil
}

Use structured logging with key-value pairs instead of string formatting. This makes logs easier to parse and query.

Not Using Proper Error Types

// Anti-pattern: Using string errors
func validateUser(user User) error {
    if user.Name == "" {
        return errors.New("name is required")
    }
    if user.Age < 0 {
        return errors.New("age cannot be negative")
    }
    return nil
}

// Better approach: Define error types
type ValidationError struct {
    Field string
    Message string
}

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

func validateUser(user User) error {
    if user.Name == "" {
        return ValidationError{Field: "name", Message: "is required"}
    }
    if user.Age < 0 {
        return ValidationError{Field: "age", Message: "cannot be negative"}
    }
    return nil
}

Define custom error types that implement the error interface for better error handling and more context.

Not Using Channels Correctly

// Anti-pattern: Not closing channels
func generateNumbers(n int) <-chan int {
    ch := make(chan int)
    go func() {
        for i := 0; i < n; i++ {
            ch <- i
        }
        // Channel is not closed
    }()
    return ch
}

// Better approach: Close channels when done
func generateNumbers(n int) <-chan int {
    ch := make(chan int)
    go func() {
        defer close(ch) // Channel is closed when the goroutine exits
        for i := 0; i < n; i++ {
            ch <- i
        }
    }()
    return ch
}

Always close channels when you’re done sending values. This signals to receivers that no more values will be sent.

Not Using Context Timeout

// Anti-pattern: No timeout for external calls
func fetchData(ctx context.Context, url string) ([]byte, error) {
    req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
    if err != nil {
        return nil, err
    }
    
    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()
    
    return ioutil.ReadAll(resp.Body)
}

// Better approach: Use context with timeout
func fetchData(url string) ([]byte, error) {
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
    defer cancel()
    
    req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
    if err != nil {
        return nil, err
    }
    
    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()
    
    return ioutil.ReadAll(resp.Body)
}

Use context.WithTimeout to set timeouts for external calls to prevent your application from hanging indefinitely.

Not Using sync.WaitGroup Correctly

// Anti-pattern: Incorrect WaitGroup usage
func processItems(items []Item) {
    var wg sync.WaitGroup
    
    for _, item := range items {
        go func() { // Bug: item is captured by reference
            wg.Add(1) // Bug: wg.Add should be called before the goroutine
            defer wg.Done()
            processItem(item)
        }()
    }
    
    wg.Wait()
}

// Better approach: Correct WaitGroup usage
func processItems(items []Item) {
    var wg sync.WaitGroup
    wg.Add(len(items)) // Add before starting goroutines
    
    for _, item := range items {
        item := item // Create a new variable for each iteration
        go func() {
            defer wg.Done()
            processItem(item)
        }()
    }
    
    wg.Wait()
}

Call wg.Add before starting goroutines and be careful with loop variables in goroutines.

Not Using Proper Concurrency Patterns

// Anti-pattern: Ad-hoc concurrency
func processItems(items []Item) []Result {
    results := make([]Result, len(items))
    var mu sync.Mutex
    
    var wg sync.WaitGroup
    wg.Add(len(items))
    
    for i, item := range items {
        i, item := i, item
        go func() {
            defer wg.Done()
            result := processItem(item)
            
            mu.Lock()
            results[i] = result
            mu.Unlock()
        }()
    }
    
    wg.Wait()
    return results
}

// Better approach: Worker pool pattern
func processItems(items []Item) []Result {
    numWorkers := runtime.NumCPU()
    jobs := make(chan Job, len(items))
    results := make(chan Result, len(items))
    
    // Start workers
    var wg sync.WaitGroup
    wg.Add(numWorkers)
    for i := 0; i < numWorkers; i++ {
        go func() {
            defer wg.Done()
            for job := range jobs {
                results <- processItem(job.Item)
            }
        }()
    }
    
    // Send jobs
    for _, item := range items {
        jobs <- Job{Item: item}
    }
    close(jobs)
    
    // Wait for workers to finish
    go func() {
        wg.Wait()
        close(results)
    }()
    
    // Collect results
    var allResults []Result
    for result := range results {
        allResults = append(allResults, result)
    }
    
    return allResults
}

Use established concurrency patterns like worker pools instead of ad-hoc concurrency.

Not Using Proper Error Wrapping

// Anti-pattern: Losing error context
func processFile(path string) error {
    data, err := ioutil.ReadFile(path)
    if err != nil {
        return err // Original context is lost
    }
    
    return processData(data)
}

// Better approach: Wrap errors to add context
func processFile(path string) error {
    data, err := ioutil.ReadFile(path)
    if err != nil {
        return fmt.Errorf("failed to read file %s: %w", path, err)
    }
    
    if err := processData(data); err != nil {
        return fmt.Errorf("failed to process data from %s: %w", path, err)
    }
    
    return nil
}

Use fmt.Errorf with the %w verb to wrap errors and add context while preserving the original error for checking with errors.Is and errors.As.

Not Using Proper Testing Techniques

// Anti-pattern: Monolithic tests
func TestUser(t *testing.T) {
    // Test creation, validation, and persistence in one test
    user := NewUser("John", 30)
    if user.Name != "John" || user.Age != 30 {
        t.Errorf("User not created correctly")
    }
    
    err := validateUser(user)
    if err != nil {
        t.Errorf("Valid user failed validation: %v", err)
    }
    
    err = saveUser(user)
    if err != nil {
        t.Errorf("Failed to save user: %v", err)
    }
}

// Better approach: Table-driven tests with subtests
func TestNewUser(t *testing.T) {
    tests := []struct {
        name     string
        username string
        age      int
        want     User
    }{
        {"Valid user", "John", 30, User{"John", 30}},
        {"Zero age", "Jane", 0, User{"Jane", 0}},
    }
    
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got := NewUser(tt.username, tt.age)
            if got != tt.want {
                t.Errorf("NewUser() = %v, want %v", got, tt.want)
            }
        })
    }
}

Use table-driven tests and subtests to make tests more maintainable and to test multiple cases easily.

Not Using go.mod for Dependency Management

// Anti-pattern: Not using go modules
// Relying on GOPATH or vendor directory

// Better approach: Use go modules
// go.mod
module github.com/example/myproject

go 1.16

require (
    github.com/pkg/errors v0.9.1
    github.com/stretchr/testify v1.7.0
)

Use Go modules (go.mod) for dependency management to ensure reproducible builds and explicit versioning.

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