PHP Dynamic Object With Array and Iterative access capability

PDAO.php

<?php

class PDAO implements \ArrayAccess, \Iterator
{
        /**
        * @var array data
        */
        protected $data     = array();
        
        /**
      	* Constructor - Create a new object, or load an existing one from data.
      	*
      	* @param array $doc data array.
      	*/
        public function __construct(array $doc = array())
      	{		
      		  $this->data     = $doc;
            foreach ($doc as $key => $value) {
                $this[$key] = $value;
            }
      	}
     
        /**
        * Checks whether a key is set on this object.
        *
        * @param string $key The key.
        * @return bool
        */
        public function __isset($key)
        {
            return isset($this->data[$key]);
        }
         
        /**
        * Get the value of a key in this object.
        * 
        * @param string $key The key.
        * @return mixed
        */
            public function __get($key)
        {
            if(isset($this->data[$key]))
            {
                return $this->data[$key];
            }
            else
            {
                return null;
            }
        }
         
        /**
        * Set the value of a key in this object.
        * 
        * @param string $key The key.
        * @param string $value The value.
        */
        public function __set($key, $value)
        {
            if ($key === null) {
                        $this->data[] = $value;
                    } else {
                        $this->data[$key] = $value;
                    }
        }
             
        /**
         * Unset a property in this object
         * @param type $name
         */
        public function __unset($name) 
        {
                if(isset($this->data[$name])) 
                {
                    unset($this->data[$name]);
                }
        }
    
        /**
        * Check if a key exist
        * @param type $offset
        * @return type
        */
       public function offsetExists($offset) 
       {
               return $this->__isset($offset);
       }

       /**
        * get value for a key
        * @param type $offset
        * @return type
        */
       public function offsetGet($offset) 
       {   
               return $this->__get($offset);
       }

       /**
        * set value for a key
        * @param type $offset
        * @param type $data
        * @return type
        */
       public function offsetSet($offset, $data) 
       {
            if (is_array($data)) {
                $data = new self($data);
            }
           $this->__set($offset, $data);
       }

       /**
        * unset a key
        * @param type $offset
        */
       public function offsetUnset($offset) 
       {
               unset($this->data[$offset]);
       }
       
       /**
        * Reset index
        * @return type
        */
       function rewind() {
           return reset($this->data);
       }

       /**
        * Return current data
        * @return type
        */
       function current() {
           return current($this->data);
       }

       /**
        * Return current key
        * @return type
        */
       function key() {
           return key($this->data);
       }

       /**
        * Return next key
        * @return type
        */
       function next() {
           return next($this->data);
       }

       /**
        * checks whether current element is valid
        * @return type
        */
       function valid() {
           return key($this->data) !== null;
       }
}