return waitFor(callable, Callable.class);
    }

    @SuppressWarnings("unchecked") // proxy for a generic class
    <V> ClosingCallable<V> waitFor(ClosingCallable<V> closingCallable) {
      return waitFor(closingCallable, ClosingCallable.class);
    }

    @SuppressWarnings("unchecked") // proxy for a generic class