foreigner_class!(class Foo {
self_type Foo;
constructor Foo::new(_: i32) -> Foo;
method Foo::f(&self, _: i32, _: i32) -> i32;
});
foreigner_class!(class Boo {
self_type Boo;
constructor Boo::new(_: i32, _: usize) -> Boo;
method Boo::f1(&self) -> &[u32];
method Boo::f2(&self) -> &[Foo];
method Boo::f3(&self) -> &[usize];
});