Created attachment 165711 [details]
Test case

(vala 0.8.0-0ubuntu1)

STR:
Subclass Clutter.Actor
Override the allocate method with:
    public override void allocate (ActorBox box, AllocationFlags flags)
Compile class

Result:
produces warning in C code
    warning: assignment from incompatible pointer type

static void test_class_init (TestClass * klass) {
	test_parent_class = g_type_class_peek_parent (klass);
	CLUTTER_ACTOR_CLASS (klass)->allocate = test_real_allocate; // <-- Here
}


Compile test case with:
valac Test.vala --pkg clutter-1.0 --save-temps