Il Tue, 18 Jul 2017 22:00:52 +0200 Stefan Salewski <mail@xxxxxxxxxxxx> scrisse: > ... > So the second parameter is of type GtkStyleProvider, which is an > interface. GtkCssProvider provides that interface, so we can pass a > variable of that type. GTK_STYLE_PROVIDER() is basically only a cast, a > re-interpretation of the bit pattern, maybe with additional security > checks. Hi Stefan, I'll give you my view that will not necessarily match the view of who wrote GInterface. Although GTK_STYLE_PROVIDER() is similar to e.g. G_OBJECT(), they are fundamentally different. While the latter matches exactly your description (a GtkCssProvider is also a GObject), the former should be considered only a check. If you dig enough in that macro you will discover this function: https://git.gnome.org/browse/glib/tree/gobject/gtype.c?h=2.52.3#n3440 G_OBJECT() is matched by the first branch (support_inheritance) while GTK_STYLE_PROVIDER() by the second one (support_interfaces). This difference is purely theorethical though, because GtkStyleProvider is not even defined. In other words one could argue that GTK_STYLE_PROVIDER() is a real cast to an undefined type. > ... > So I assume, > that for all functions which has interfaces as parameters, I can just > pass all objects (gobjects) which provides that interface? Yes. > I even guess hat interfaces are fully abstract entities, so we will > never pass an instance of an interface, but always only objects > providing the interface. So we have only to provide functions which can > accepts all the objects providing the that interface, but we do not > really need functions which would accepts the interface parameter type > itself? Correct. As pointed out before, even in C interface instances are only dummy typedefs. I see interfaces as a "contract" that (1) enforces an object to implement some feature (properties and/or methods) and consequently (2) gives the users a common API that can be used across unrelated objects. Ciao. -- Nicola _______________________________________________ gtk-list mailing list gtk-list@xxxxxxxxx https://mail.gnome.org/mailman/listinfo/gtk-list
