They're not erased all the way, they're only erased down into the root type for all objects. So you've still got some type information left (namely, that it's

They're not erased all the way, they're only erased down into the root type for all objects. So you've still got some type information left (namely, that it's an Object), and any types that are not Objects are officially banned from the generics system. Hence the need to dress them up as washerwomen and sneak them in through the service entrance.