Consider the following code. What change must be made to the class for the code to work as written?

class Magic {

protected $v = array("a" => 1, "b" => 2, "c" => 3);

public function __get($v) {

return $this->v[$v];

}

}

$m = new Magic();

$m->d[] = 4;

echo $m->d[0];