+// Why a pointer here? Because it has zero initialization at load
+// time which is guaranteed to come before the static initializations
+// of all constructors for static expressions of the classes created
+// by ADD_SCM_INIT_FUNC. The vector data type does not have load-time
+// initialization and might clear out already set callbacks at the
+// time it is initialized since there is no implied order among
+// non-trivial constructors for static data in separate compilation
+// units. So we need a trivial type like a pointer instead.
+