gistfile1.php

<?php

class Obj {
  public $mod = false;
}

class Example {
  protected $items = array();
  
  public function getItems()
  {
    return $this->items;
  }
  
  public function addItem($item)
  {
    $this->items[] = $item;
  }
}

$item = new Obj();

$example = new Example();
$example->addItem($item);

$items = $example->getItems();
$items[0]->mod = true;

var_dump($example->getItems());