QTagWidget::indexOf should take a const QWidget*

class Edit : QPlainTextEdit
{
Q_OBJECT
public:
   Edit(const QTabWidget& parent) : _parent{parent} {}
   // would like to do: 
   // int myIndex() const { return _parent.indexOf(this)};

   // have to do:
   int myIndex() const { return _parent.indexOf(const_cast<Edit*>(this));};

private:
   const QTabWidget& _parent;
};