// Go test file
package main
import (
"fmt"
"net/http"
"encoding/json"
db "database/sql"
)
// Struct definition
type User struct {
ID int `json:"id"`
Name string `json:"name"`
Email string `json:"email"`
}
// Interface definition
type Service interface {
GetUser(id int) (*User, error)
CreateUser(user User) error
DeleteUser(id int) error
}
// Type alias
type UserID int
// Constants
const (
MaxUsers = 100
DefaultTimeout = 30
)
// Variables
var (
userCache map[int]*User
logger *Logger
)
// Struct with methods
type UserService struct {
db *db.DB
cache map[int]*User
}
// Method with pointer receiver
func (s *UserService) GetUser(id int) (*User, error) {
if user, ok := s.cache[id]; ok {
return user, nil
}
user := &User{}
err := s.db.QueryRow("SELECT * FROM users WHERE id = ?", id).Scan(&user.ID, &user.Name, &user.Email)
if err != nil {
return nil, err
}
s.cache[id] = user
return user, nil
}
// Method with value receiver
func (s UserService) String() string {
return fmt.Sprintf("UserService with %d cached users", len(s.cache))
}
// Function
func NewUserService(database *db.DB) *UserService {
return &UserService{
db: database,
cache: make(map[int]*User),
}
}
// Generic-like function using interface{}
func ProcessData(data interface{}) error {
switch v := data.(type) {
case *User:
return processUser(v)
case []User:
return processUsers(v)
default:
return fmt.Errorf("unsupported type: %T", v)
}
}
func processUser(user *User) error {
// Process single user
logger.Log("Processing user: " + user.Name)
return nil
}
func processUsers(users []User) error {
for _, user := range users {
if err := processUser(&user); err != nil {
return err
}
}
return nil
}
// HTTP handler
func userHandler(w http.ResponseWriter, r *http.Request) {
service := NewUserService(nil)
user, err := service.GetUser(1)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
json.NewEncoder(w).Encode(user)
}
// Logger type
type Logger struct {
prefix string
}
func (l *Logger) Log(message string) {
fmt.Printf("%s: %s\n", l.prefix, message)
}
func main() {
logger = &Logger{prefix: "APP"}
userCache = make(map[int]*User)
http.HandleFunc("/user", userHandler)
http.ListenAndServe(":8080", nil)
}
