library test;

int getInt() => 0;
num getNum() => 0;
double getDouble() => 0.0;

abstract class Base<T, U> {
  T operator [](String s) => getValue(s);
  void operator []=(String s, U v) => setValue(s, v);
  T getValue(String s);
  void setValue(String s, U v);
}

abstract class Base2<T, U> {
  T? operator [](String s) => getValue(s);
  void operator []=(String s, U? v) => setValue(s, v);
  T? getValue(String s);
  void setValue(String s, U? v);
}

abstract class Test1a extends Base<int, int> {
  void test() {}
}

abstract class Test1b extends Base2<int, int> {
  void test() {}
}

abstract class Test2a extends Base<int, num> {
  void test() {}
}

abstract class Test2b extends Base2<int, num> {
  void test() {}
}

abstract class Test3a extends Base<int, double> {
  void test() {}
}

abstract class Test3b extends Base2<int, double> {
  void test() {}
}

abstract class Test4a extends Base<num, int> {
  void test() {}
}

abstract class Test4b extends Base2<num, int> {
  void test() {}
}

abstract class Test5a extends Base<num, num> {
  void test() {}
}

abstract class Test5b extends Base2<num, num> {
  void test() {}
}

abstract class Test6a extends Base<num, double> {
  void test() {}
}

abstract class Test6b extends Base2<num, double> {
  void test() {}
}

abstract class Test7a extends Base<double, int> {
  void test() {}
}

abstract class Test7b extends Base2<double, int> {
  void test() {}
}

abstract class Test8a extends Base<double, num> {
  void test() {}
}

abstract class Test8b extends Base2<double, num> {
  void test() {}
}

abstract class Test9a extends Base<double, double> {
  void test() {}
}

abstract class Test9b extends Base2<double, double> {
  void test() {}
}

main() {}