Description:
------------
It is not possible to modify an element of an array returned by ArrayAccess::offsetGet(). Also the error message suggests that offsetGet() should return a reference but it is not possible due to the offsetGet() original declaration.

Reproduce code:
---------------
<?
class obj_array implements ArrayAccess
{
        private $array;

        public function __construct ($array)
        {
                $this->array = $array;
        }

        public function offsetExists ($index)
        {
                return (array_key_exists ($index, $this->array));
        }

        public function offsetGet ($index)
        {
                return ($this->array [$index]);
        }

        public function offsetSet ($index, $value)
        {
                $this->array [$index] = $value;
        }

        public function offsetUnset ($index)
        {
                unset ($this->array [$index]);
        }
}

$obj = new obj_array (array ("index_1" => array ("index_2" => 123)));
$obj ["index_1"]["index_2"] = 456;
?>


Expected result:
----------------
Nothing should be displayed when the code is run.

Actual result:
--------------
Fatal error: Objects used as arrays in post/pre increment/decrement must return values by reference in /archive/try.php on line 33