PHP - 转换对象到数组 - 空数组

I'm trying to convert an object to an array but I always end up with an empty array.

The object is the following:

DOMElement Object
(
[tagName] => span
[schemaTypeInfo] => 
[nodeName] => span
[nodeValue] => 
[nodeType] => 1
[parentNode] => (object value omitted)
[childNodes] => (object value omitted)
[firstChild] => 
[lastChild] => 
[previousSibling] => (object value omitted)
[nextSibling] => (object value omitted)
[attributes] => (object value omitted)
[ownerDocument] => (object value omitted)
[namespaceURI] => 
[prefix] => 
[localName] => span
[baseURI] => 
[textContent] => 
)

This object is store in $my_object

If I try this:

$test = get_object_vars($my_object);
print_r($test);

I get an empty array.

If I try this:

$test = (array)$my_object;
print_r($test);

I also get an empty array

If I try this:

$array = json_decode(json_encode($my_object), true);

Same result, empty array.

Am I doing something wrong ? Seemed fairly simple but I don't find a way to convert my object into an array.

Any idea?

Thanks

Laurent