code: func (logger *Logger) GetTag() string {
  	goID := logger.curGoroutineID()
  	if tagVal, found := logger.tagMap.Load(goID); !found {
  		return ""
  	} else if tag, ok := tagVal.(string); ok {
  		return tag
  	}
  	panic(fmt.Errorf("cannot cast log tag from map to string"))
  }
docs: // GetTag returns the tag identifying the caller's go routine.