def merge(self, rule):
        """
        Migrate all stateful attributes from the old rule
        """
        with self._lock:
            self._request_count = rule.request_count
            self._borrow_count = rule.borrow_count
            self._sampled_count = rule.sampled_count
            self._reservoir = rule.reservoir
            rule.reservoir = None
Migrate all stateful attributes from the old rule