main.dart

class G {}

class Foo<T extends G, F extends Foo<T, F, B>, B extends Bar<T, F, B>> {}

class Bar<T extends G, F extends Foo<T, F, B>, B extends Bar<T, F, B>> {}

class SubFoo extends Foo<G, SubFoo, SubBar> {}

class SubBar extends Bar<G, SubFoo, SubBar> {}

String works<T extends G, F extends Foo<T, F, B>, B extends Bar<T, F, B>>(Foo<T, F, B> foo) => foo.runtimeType.toString();

String fails<T extends G, F extends Foo<T, F, B>, B extends Bar<T, F, B>>(F foo) => foo.runtimeType.toString();

void main() {
  print(works(SubFoo()));
  print(fails(SubFoo()));
}