* @return bool

     */

    public function offsetExists($key)

    {

        return array_key_exists($key, $this->items);

    }

 

    /**

     * Get an item at a given offset.

     *

     * @param  mixed  $key

     * @return mixed

     */

    public function offsetGet($key)

    {

        return $this->items[$key];

    }

 

    /**

     * Set the item at a given offset.

     *

     * @param  mixed  $key

     * @param  mixed  $value

     * @return void

     */

    public function offsetSet($key, $value)

    {

        if (is_null($key)) {

            $this->items[] = $value;

        } else {

            $this->items[$key] = $value;