code: func (mem *Memory) Set(key string, val interface{}, timeout time.Duration) (err error) {
  	mem.Lock()
  	defer mem.Unlock()
  
  	mem.data[key] = &data{
  		Data:    val,
  		Expired: time.Now().Add(timeout),
  	}
  	return nil
  }
docs: //Set cached value with key and expire time.