code: func (h *Heap) GetByKey(key string) (interface{}, bool, error) {
  	h.lock.RLock()
  	defer h.lock.RUnlock()
  	item, exists := h.data.items[key]
  	if !exists {
  		return nil, false, nil
  	}
  	return item.obj, true, nil
  }
docs: // GetByKey returns the requested item, or sets exists=false.