Golang装饰者模式扩展功能实践

type UserService interface {
  GetUser(id int) string
}

type userService struct{}

func (s *userService) GetUser(id int) string {
  // 模拟耗时操作
  return fmt.Sprintf("User-%d", id)
}

type loggingDecorator struct {
  service UserService
}

func NewLoggingDecorator(s UserService) UserService {
  return &loggingDecorator{service: s}
}

func (d *loggingDecorator) GetUser(id int) string {
  fmt.Printf("Calling GetUser with ID: %d\n", id)
  result := d.service.GetUser(id)
  fmt.Printf("GetUser returned: %s\n", result)
  return result
}

type cacheDecorator struct {
  service UserService
  cache   map[int]string
}

func NewCacheDecorator(s UserService) UserService {
  return &cacheDecorator{
    service: s,
    cache:   make(map[int]string),
  }
}

func (c *cacheDecorator) GetUser(id int) string {
  if name, ok := c.cache[id]; ok {
    return name
  }

  name := c.service.GetUser(id)
  c.cache[id] = name
  return name
}

service := &userService{}
cached := NewCacheDecorator(service)
logged := NewLoggingDecorator(cached)

logged.GetUser(42) // 先走日志，再查缓存，最后调用真实服务
logged.GetUser(42) // 缓存生效，但仍会打印日志