Set a referenced variable to a newly initialized class - php

Question

I have a method, which takes a reference
// CarService.php
public function getCars(&$carCollection = null)
{
$promise = // guzzle request for getting all cars would be here
$promise->then(function (ResponseInterface $response) use (&$carCollection) {
$cars= json_decode($response->getBody(), true);
$carCollection= new CarCollection($cars);
});
}
However, when accessing the collection and trying to reuse it, I'm getting the error
Argument 1 passed to {placeholder} must be an instance of {placeholder}, null given
I know that the reason for this is, that the constructor returns nothing, but how can I still assign my variable to a new instance of the CarCollection (which extends Doctrine's ArrayCollection)
I even tried it with a static method as a work around
// CarCollection.php
public static function create(array $cars): CarCollection
{
$carCollection = new CarCollection($cars);
return $carCollection;
}
// CarService.php
public function getCars(&$carCollection = null)
{
$cars = // curl request for getting all cars would be here
$carCollection = CarCollection::create($cars)
}
but it's still null. Why is that? How can I set a referenced variable to a new class?
I access the method like this
$carService = $this->get('tzfrs.vehicle.services.car');
$carCollection = null;
$promises = [
$carService->getCars($carCollection)
];
\GuzzleHttp\Promise\unwrap($promises);
var_dump($carCollection); // null
When I set the reference directly, eg.
// CarService.php
public function getCars(&$carCollection = null)
{
$carCollection = new CarCollection([]);
}
it works without any problems. Seems like the callback is somehow the problem.
Whoever downvoted this, can you please elaborate why and why you voted to close?

Answer 1

I might be misunderstanding the question, but you should be able to modify an object when passing by reference. See here for an example: https://3v4l.org/KtFvZ
In the later example code that you added, you shouldn't pass $carCollection by reference, the & should only be in the method/function defintion, not provided when you call it. I don't think that is your problem though, that should be throwing an error in php7.