A convenience macro to ease interface addition in the
of G_DEFINE_TYPE_WITH_CODE() or G_DEFINE_ABSTRACT_TYPE_WITH_CODE().
See G_DEFINE_TYPE_EXTENDED() for an example.
Note that this macro can only be used together with the
macros, since it depends on variable names from those macros.
Available since: 2.4
This function is not directly available to language bindings.