[PyKDE] sip: C++ virtual methods

[Patrick Stinson]

great, thanks Jim. I think I'll get it now.

On Wednesday 24 September 2003 09:39, Jim Bublitz wrote:
> On Wednesday September 24 2003 10:04, Patrick Stinson wrote:
> > in progression:
> >
> > Does the %ConvertToSubClassCode directive require some sort of
> > class identification mechanism to be written into the original
> > cpp library code? QEvent returns an enumerated value in
> > type(), as well ass QApplication and some others, and QObject
> > has QObject::className() that returns a string identifier.
> > that can be used in conjuction with sipMapStringToClass() and
> > a sipStringTypeClassMap struct.
> >
> > Does this mean I have to modify my cpp library to add some
> > sort of class identifier for classs/subclasses if I want
> > polymorphic return values in my python functions?
>
> I had the same question, but unfortunately I posted it to Phil
> twice rather once to him and once to the list. Here's our
> exchange:
>
> On Monday 22 September 2003 4:47 pm, you wrote:
> > On Monday September 22 2003 02:03, Phil Thompson wrote:
> > > > media = PK.CreateMediaLayer("./track.ogg")
> > > > while not media.AtEnd():
> > > >   media.Read()
> > >
> > > What do you get when you "print media"? If you get a
> > > PK_MediaLayer instance then maybe you haven't implemented
> > > %ConvertToSubClassCode properly.
>
> ===== my post =======
>
> > From copying PyQt code, I understand (I think) how to implement
> > %ConvertToSubClassCode for hierarchies like QObject or QEvent -
> > but those both have methods that return some kind of type
> > identifier (like QObject::className() ).
> >
> > If a hierarchy of classes *doesn't* have a method like that,
> > how do you do the %ConvertToSubClassCode block? Use the C++
> > RTTI typeid() function?
> >
> > eg:
> >
> > class A {};
> > class B : public A {};
> >
> > ---
> >
> > %HeaderCode
> > #include <typeinfo>
> > %End
> >
> > %ConvertToSubClassCode
> >     static sipStringTypeClassMap map[] = {
> >       {sipName_B, &sipClass_B},
> >        ...
> >     };
> >
> >     sipClass = sipMapStringToClass(
> >          typeid (*sipCpp),
> >          map, sizeof (map)/sizeof (map[0]));
> > %End
> >
> > Would that work? I'm assuming sipCpp is already of the
> > subclass'  type (or sipCpp->className () wouldn't work?), and
> > this is just fixing the corresponding PyObject's type?
>
> ===== Phil's reply =======
>
> There are potential problems there because the C++ instance might
> be "QObject"  or "sipQObject", but that's just a case of setting
> the table up properly. It  doesn't really matter how it is
> implemented, so long as a valid PyObject * is returned that is
> actually a Python class object.