class ContentIterator extends RecursiveIteratorIterator
{
    private $_ordinal = 0;

    public function __construct()
    {
        parent::__construct(new RecursiveArrayIterator(func_get_args()));
    }

    public function key()
    {
        return $this->_ordinal;
    }

    public function getChildren()
    {
        $current = $this->current();
        if (property_exists($current,'array')) return new RecursiveArrayIterator(array_values($current->array()));
        throw new Exception('Shouldn't reach here!');
    }

    public function hasChildren()
    {
        $current = $this->current();
        return is_array($current) || $current instanceof Traversable;
    }

    public function next()
    {
        parent::next();
        ++$this->_ordinal;
    }

    public function rewind()
    {
        parent::rewind();
        $this->_ordinal = 0;
    }

}

class TestSource {
  public $array = ['a','b','c'];
}

foreach (new ContentIterator(new TestSource) as $key => $value)
    echo "$key => ".json_encode($value)."n";

0 => "a"
1 => "b"
2 => "c"

0 => ["a","b","c"]