带有ARRAY_AS_PROPS的嵌套ArrayObject

Question

I'm playing with ArrayObject since some days now, but there is a trick that I can't do.

What I want to do :

MyClass extends ArrayObject {
    public function __construct($input = []) {
        parent::__construct($input, self::ARRAY_AS_PROPS);
    }
}

$a = new MyClass();
$a->foo = 'bar';
var_dump($a->getArrayCopy()); // there should be only one key : "foo"
$a->bar->baz = 'foo';
var_dump($a->getArrayCopy()); // there should be only two keys : "foo", "bar"
echo get_class($a->bar) . "
"; // should be MyClass

But $a->bar is a stdClass, and I have a pretty warning in bonus

If I disable the ARRAY_AS_PROPS flag and override the __get and __set methods I'm close :

function __get($key) {
   if (! $this->offsetExists($key)) {
       $this->offsetSet($key, new self);
   }
   return $this->offsetGet($key)
}

But then, I have this issue :

$a = new MyClass();
$a->foo = 'bar';
var_dump($a->getArrayCopy()); // there is one key ("foo") which is correct

// but when I do anything with the key without affecting some data
isset($a->bar);
var_dump($a->getArrayCopy()); // Now I also have the key "bar" which is not correct

Any suggestion ?