code: func (m *boxMap) Range(f func(key string, value *Box) bool) {
  	m.data.Range(func(k, v interface{}) bool {
  		key, ok := k.(string)
  		if !ok {
  			return false
  		}
  		value, ok := v.(*Box)
  		if !ok {
  			return false
  		}
  		return f(key, value)
  	})
  }
docs: // Range over the *Box values in the map