Laravel: External variable in callback for chunk

I am trying to implement search in Laravel. I want to search on models. Since there can be many records in the database, I am trying the chunk function.

public function searchLeads($param)
    {
        $results = array();

        // get all leads
        Lead::chunk(100, function($leads) use ($results, $param) {
            // search in name
            $results = array_merge($results, $this->repository->searchInName($leads, $param));

            // search in email
            $results = array_merge($results, $this->repository->searchInEmail($leads, $param));

           // and so on ...
    }

    // eliminate duplicates
    $collection = collect($results);
    $collection = $collection->unique();

    $results = $collection->all();

    dd($results);
    // return $results;
}

Note: The searchIn... functions return array of results and are working as expected.

When I try the above code, I get an empty array. So I changed the following line (added a reference & to $results).

Lead::chunk(100, function($leads) use (&$results, $param) {

Now I get the expected output.

My question is, am I doing this the correct way? Have I stumbled upon the right solution, or am I missing something that might introduce bugs in the code?

via Chebli Mohamed