- var_dump: documentation ( source)
<?php
$object = new ArrayObject([], ArrayObject::ARRAY_AS_PROPS);
$object['a'] = 'test';
var_dump($object['a'] == $object->a); //bool(true)
$object->month = 'january';
echo $object['month']; // january
$object['day'] = 'saturday';
echo $object->day; // saturday