public function add($pCoord, Cell $cell)
    {
        if ($pCoord !== $this->currentCoordinate) {
            $this->storeCurrentCell();
        }
        $this->index[$pCoord] = true;

        $this->currentCoordinate = $pCoord;
        $this->currentCell = $cell;
        $this->currentCellIsDirty = true;

        return $cell;
    }