Syncing unintentionally skewed 6model header, as per jnthn++

src/binder/sixmodelobject.h

@@ -350,6 +350,24 @@ struct SixModel_REPROps {
 #define IS_CONCRETE(o)         (!PObj_flag_TEST(private0, (o)))
 #define MARK_AS_TYPE_OBJECT(o) PObj_flag_SET(private0, (o))
 
+/* Write barriers for noticing changes to objects or STables with an SC. */
+typedef void (* obj_sc_barrier_func) (PARROT_INTERP, PMC *obj);
+typedef void (* st_sc_barrier_func) (PARROT_INTERP, STable *st);
+#define OBJ_SC_WRITE_BARRIER(o) \
+    if (SC_PMC(o)) { \
+        ((obj_sc_barrier_func) \
+        D2FPTR(VTABLE_get_pointer(interp, \
+            VTABLE_get_pmc_keyed_str(interp, interp->root_namespace, \
+                Parrot_str_new_constant(interp, "_OBJ_SC_BARRIER")))))(interp, o); \
+    }
+#define ST_SC_WRITE_BARRIER(st) \
+    if ((st)->sc) { \
+        ((st_sc_barrier_func) \
+        D2FPTR(VTABLE_get_pointer(interp, \
+            VTABLE_get_pmc_keyed_str(interp, interp->root_namespace, \
+                Parrot_str_new_constant(interp, "_ST_SC_BARRIER")))))(interp, st); \
+    }
+
 /* Object model initialization. */
 void SixModelObject_initialize(PARROT_INTERP, PMC **knowhow, PMC **knowhow_attribute);
 
@@ -360,7 +378,9 @@ PMC * create_stable(PARROT_INTERP, REPROps *REPR, PMC *HOW);
 PMC * decontainerize(PARROT_INTERP, PMC *var);
 
 /* Dynamic representation registration. */
-typedef INTVAL (* rf) (PARROT_INTERP, STRING *name, REPROps * (*reg) (PARROT_INTERP, void *, void *));
+typedef PMC * (*wrap_object_t)(PARROT_INTERP, void *obj);
+typedef PMC * (*create_stable_t)(PARROT_INTERP, REPROps *REPR, PMC *HOW);
+typedef INTVAL (* rf) (PARROT_INTERP, STRING *name, REPROps * (*reg) (PARROT_INTERP, wrap_object_t, create_stable_t));
 #define REGISTER_DYNAMIC_REPR(interp, name, reg_func) \
     ((rf) \
         VTABLE_get_pointer(interp, \