Re: Gtk::Widget as virtual base

[Antonio Coralles <noche suapie reflex at>]

Antonio Coralles wrote:

> jyotirmoy bhattacharya wrote:
>
>> I want to use an abstract class derived from Gtk::Widget and then
>> derive different classes which use particular widgets to display
>> themselves.
>>
>> That is, I want to do something like
>>
>> class vwidget: public virtual Gtk::Widget
>> {
>>  public:
>>   virtual void magic()=0;
>> };
>>
>> class mywidget: public vwidget, public Gtk::HBox
>> {
>>  public:
>>   void magic() {x=1;}
>>  private:
>>   int x;
>> };
>>
>> mywidget m;
>>
>> But when I compile this I get the following errors:
>> document.h:86: error: no unique final overrider for `virtual void
>> Glib::ObjectBase::destroy_notify_()' in `mywidget'
>> document.h:86: error: no unique final overrider for `virtual void
>> Glib::ObjectBase::set_manage()' in `mywidget'
>> document.h:86: error: no unique final overrider for `virtual void
>> Glib::ObjectBase::destroy_notify_()' in `mywidget'
>> document.h:86: error: no unique final overrider for `virtual void
>> Glib::ObjectBase::set_manage()' in `mywidget'
>>
> The problem is that Gtk::HBox is also an Gtk::Widget and thus for
> example Gtk::Hbox has methods like Gtk::Widget like set_manage(),
> destroy_notify_(), ... . How can the compiler know if you want to use
> Gtk::Widget::set_manage() or Gtk::HBox::set_manage() in your mywidget
> class ? If you really want to do this, you have to make that decission
> yourself for every method the compiler complains about.
>
> class mywidget: public vwidget, public Gtk::HBox
> {
>  public:
>   void magic() {x=1;}
>
>   // this are unique final overriders
>   void destroy_notify() { vwwidget::destroy_notify(); }
>   void set_manage() { Gtk::HBox::set_manage(); }
>   // ....
>  
>  private:
>   int x;
> };
>
> Maybe may also be interested in
> http://www.parashift.com/c++-faq-lite/multiple-inheritance.html#faq-25.11.
>
> Hope this helps,
> Antonio

Maybe you can resolve most of this ambiguitys with using virtual
inheritance.  The problem is,  that  [  keyword diamond inheritance ]
for doing this, both classes you inherit from should use virtual
inhertitance from Gtk::Widget. I guess this is not the case for
Gtk::HBox, so using virtual inheritance for vwwidget only doesn't help.
Maybe there is an easier way to do what you want to do ...
Antonio

>
>> I am using gtkmm 2.4 and g++ 3.4.2
>>
>> Not making Gtk::Widget virtual in the definition of vwidget leads to
>> the same errors and
>> I don't think that would solve my problem anyway.
>>
>> I would be grateful if the subscribers of this list can suggest a way
>> out of my problem.
>>
>> --Jyotirmoy
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