I'm new to symfony 4 and tried to write my own function for yml nelmio/alice, but after I ran bin/console doctrine:fixtures:load , I got this error:
In DeepCopy.php line 177:
The class "ReflectionClass" is not cloneable.
Here is my fixtures.yml file:
App\Entity\Post:
post_{1..10}:
    title: <customFunction()>
Here is my AppFixture.php file:
<?php
namespace App\DataFixtures;
use Doctrine\Bundle\FixturesBundle\Fixture;
use Doctrine\Common\Persistence\ObjectManager;
use Nelmio\Alice\Loader\NativeLoader;
class AppFixtures extends Fixture
{
    public function load(ObjectManager $manager)
    {
        $loader = new NativeLoader();
        $objectSet = $loader->loadFile(__DIR__.'/Fixtures.yml',
            [
                'providers' => [$this]
            ]
        )->getObjects();
        foreach($objectSet as $object) {
            $manager->persist($object);
        }
        $manager->flush();
    }
    public function customFunction() {
        // Some Calculations
        return 'Yep! I have got my bonus';
    }
}