Re: rework of the Gtk2-Perl type system

[Christian Borup <borup borup com>]

On fre, 2003-03-21 at 03:52, muppet wrote:
> As i have mentioned before and you are probably sick of hearing, i have
> an independent, GObject-based C library that i wish to bind to perl in
> such a way that i can use its objects seamlessly with gtk objects, e.g.,
> binding callbacks and packing my library's widgets into windows and
> other normal gobject/gtk things, similar to how the Gnome2 package
> works.

I'm hoping to wrap Evolutions CalClient once gtk2 evolution is stable
enough for everyday use (it may be already - but thats not the).
So I'd really like to see something like this.

[massive snipage]

> I propose something like
>
>    void gtk2_perl_register_class_mapping (const char * class,
>                                           const char * package,
>                                           gboolean require);
>
> Using a string for the class name instead of a GType allows us to
> specify mappings for non GObject types (structs and boxed types).  The
> "require" parameter lets you specify whether the class has a pm that
> must be loaded.

This fills the requirements I can imagine, at the moment.

> For simplicity, i imagine the class mappings as being one-to-one:
>
>    GtkWidget <=> Gtk2::Widget
>    GdkWindow <=> Gtk2::Gdk::Window
>    GdkEventKey <=> Gtk2::Gdk::Event::Key
>    PangoFontDescription <=> Gtk2::Pango::FontDescription
>    GnomeAbout <=> Gnome2::About
>    MylibFooBar <=> Mylib::FooBar
>
> With one-to-one mappings, get_class_from_classname could return a
> pointer that need not be freed, and thus avoid memory leaks.
>
> On the other hand, it might also be possible to do something like
>
>    void gtk2_perl_register_class_mapping_rule (char * perl_code_to_eval)
>
> which would allow you somehow to specify a substitution pattern for a
> whole set of mappings, to be run as a code reference, and successful
> results cached to avoid running it again.  I am willing to implement
> this, but i want help designing that portion of the interface.

This would be very Perl'ish, but I don't see an immediate need for it.

> get_class and get_class_from_classname should be renamed to avoid both
> symbol clashes (the module must be loaded with RTLD_GLOBAL!) and the
> confusion of calling everything classes.  i propose:
>
>   char * gtk2_perl_get_package_from_gobject (GObject *)
>   char * gtk2_perl_get_package_from_gtype (GType)
>   char * gtk2_perl_get_package_from_classname (char *)
>      retrieve package names
>
>   GType gtk2_perl_get_type_from_package (char *)
>   char * gtk2_perl_get_classname_from_package (char *)
>      the other way 'round

Your proposal seems sound to me.
Could get_class and get_class_from_classname not be kept as defines, to
let the existing code live on?

> Also, we could let the GType system do a lot of work for us by
> implementing @ISA as a tied variable which uses
> gtk2_perl_get_package_from_class, g_type_parent, and
> g_type_get_class_from_package.

Sounds cool.
How would it perform? 
And would it mess up the optimisations of method lookups? I assume not
as the mappings should be pretty much stable. 
Not sure how it would work though (which @ISA should be tied), have you
got any examples of modules doing this?  

Sorry for the late reply.

./borup