Change chart type according to the selected filter

in my chart widget i'm using this code to change the chart type according to the selected filter but it doesnt work,
any idea ?

 protected function getType(): string
    {
        return $this->filter == 'date' ? 'line' : 'bar';
    }

 protected function getType(): string
    {
        return $this->filter == 'date' ? 'line' : 'bar';
    }