-#define typesafe_cb_def(rtype, fn, arg) \
- cast_if_any(rtype (*)(void *), (fn), (fn)+0, \
- rtype (*)(typeof(*arg)*), \
- rtype (*)(const typeof(*arg)*), \
+#define typesafe_cb_def(rtype, fn, arg) \
+ cast_if_any(rtype (*)(void *), (fn), 0?(fn):(fn), \
+ rtype (*)(typeof(*arg)*), \
+ rtype (*)(const typeof(*arg)*), \