GInterface on a per-instance-basis

[Ronald Bultje <rbultje ronald bitfreak net>]

Hey,

I need an object that implements an interface in certain circumstances,
but not all (but it has to be the same object!). In these other cases,
the interface cast should return NULL (or something similar that tells
me that it doesn't implement this interface). GInterface seems like the
way to go, but is there any way in which I can implement them on a
per-instance basis rather than on a per-class basis? I didn't see any by
looking at the documentation
(http://www.gnome.org/~mathieu/gobject/main.html).

Thanks,

Ronald

-- 
Ronald Bultje <rbultje ronald bitfreak net>