TpDBusPropertiesMixinClass currently has to be a public field of any class wanting to use it, even if that class would just set the list of interfaces to the empty list. This is kind of a waste of 8 gpointer-widths. Perhaps passing a zero offset to tp_dbus_properties_mixin_class_init could be taken to mean that there is no MixinClass in the class, and that all interfaces for which properties should be implemented will be set up with tp_dbus_properties_mixin_implement_interface.
This was fixed in 0.7.15.
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