// @dart = 2.9
class A1 {}

extension A2 on A1 {
  A1 method1() {}
  A1 method2<T>(T o) {}
  A1 method3<T>([T o]) {}
  A1 method4<T>({T o}) {}
}

class B1<T> {}

extension B2<T> on B1<T> {
  B1<T> method1() {}
  B1<T> method2<S>(S o) {}
}

main() {}