// @dart = 2.9
library test;

import 'dart:async';

T f<T>() => null;

class B<T> {
  void operator []=(Map<int, T> x, List<T> y) {}
}

class C<U> extends B<Future<U>> {
  void operator []=(Object x, Object y) {}
  void h() {}
}

main() {}