declare(strict_types=1);

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormFactory;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\Form\FormRegistry;
use Symfony\Component\Form\ResolvedFormTypeFactory;

require_once __DIR__.'/vendor/autoload.php';

class ThingType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('name', null, [
                'empty_data' => '',
            ])
            ->add('closure', null, [
                'empty_data' => function (FormInterface $form) {
                    return '';
                },
            ])
        ;
    }
}

$formFactory = new FormFactory(new FormRegistry([], new ResolvedFormTypeFactory()));
$form = $formFactory->create(ThingType::class);
$form->submit([]);
dump($form->getData());