RE: signals versus vfuncs

[Murray Cumming Comneon com]

> Actually it's something like:
> register a new type for the C++ instance (to enable vfunc 
> overriding), 
> override every vfunc by a wrapper (static [C like] member functions) 
> which calls the virtual member function [with C++ wrapped arguments] 
> (which in turn, if not overridden, unwraps the arguments and 
> calls the 
> original gtk+ functions). This costs some overhead for each 
> vfunc call 
> (additional indirection). [Actually the gtkmm implementation 
> shortcuts 
> wrapping/unwrapping and the middle indirection if possible]

An important part of this is that we can always get the C++ instance from
the C instance. We use quarks with g_object_set_data() to store a pointer to
the 1 and only C++ wrapper instance in the C instance. Without that, the
overriden C vfunc in gtkmm would not be able to call the C++ instance's
method. You can see some of this in Glib::ObjectBase:
http://cvs.gnome.org/lxr/source/glibmm/glib/glibmm/objectbase.cc#150

I see that Christof understands gtkmm internals very well. I'll be sending
relevant patch requests to him in future.

Murray Cumming
www.murrayc.com
murrayc usa net