POC dynamic form in symfony 3

DefaultController.php

<?php

namespace DppBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Symfony\Component\Form\Extension\Core\Type\SubmitType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Validator\Constraints\NotBlank;

class DefaultController extends Controller
{
    /**
     * @Route("/", name="home")
     */
    public function indexAction(Request $request)
    {
        $form = $this->getDynamicForm();

        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            // ... perform some action, such as saving the task to the database

            return $this->redirectToRoute('home');
        }

        return $this->render('DppBundle:default:index.html.twig', array(
            'form' => $form->createView(),
        ));
    }

    protected function getDynamicForm() {
        $formBuilder = $this->createFormBuilder();
        $fields = $this->getFormFields();

        foreach($fields as $field) {
            $formBuilder->add($field['name'], $field['class'], $field['options']);
        }

        return $formBuilder->getForm();
    }

    public function getFormFields() {
        $fieldsDefault = [
            'firstName' => [
                'name' =>'firstName',
                'class' => TextType::class,
                'options' => []
            ],
            'lastName' => [
                'name' => 'lastName',
                'class' => TextType::class,
                'options' => [],
            ],
            'save' => [
                'name' => 'save',
                'class' => SubmitType::class,
                'options' => [],
            ]
        ];
        // get if form somewhere else
        $fieldsOverWrite = [
            'firstName' => [
                'options' => [
                    'constraints' => array(
                        new NotBlank(),
                    ),
                ]
            ],
            'save' => [
                'options' => [
                    'label' => 'Save overwrite'
                ]
            ]
        ];

        $fields = array_merge_recursive($fieldsDefault, $fieldsOverWrite);

        foreach($fieldsDefault as $fieldName => $metaData) {
            if(!isset($fieldsOverWrite[$fieldName])) {
                unset($fields[$fieldName]);
            }
        }

        return $fields;
    }
}