How the hack (doesn't) handles generic classes

BaseRepository.php

<?hh namespace Repositories\Generics;

class BaseRepository<T>
{
    /**
     * Saves the model 
     * @param  T $model
     * @return bool true if the model was saved      
     */
    public function save(T $model)
    {
        var_dump(gettype($model));
    }
}

BaseRepositoryTest.php

<?hh namespace Tests\Repositories\Generics;

use TestCase;
use Repositories\Generics\BaseRepository;
use User;
use App;
use ReflectionClass;

class BaseRepository extends TestCase
{
    /**
     * The user repository
     * 
     * @var UserRepository
     */
    private $userRepository;

    public function testSave()
    {
        $user = App::make('User');
        $userRepo = new BaseRepository<User>();
        // This shouldn't work but it does.
        $userRepo->save('string');
        $userRepo->save($user);
    }
}