abstract class GetterSetter{
    protected $variables = array();

    public function __get($name){
        if (isset($this->variables[$name]){
            return $this->variable[$name]['value'];
        }
        throw new Exception($name . " not a member");
    }

    public function __set($name,$value){
        if (isset($this->variable[$name]){
            if (isset($this->variables[$name]['protected'] && $this->variables[$name]['protected']) throw new Excpetion('not allowed to edit');
            $this->variables[$name]['value']=$value;
        }
        throw new Exception($name . " not a member");
    }
}

class Example extends GetterSetter{
    protected $variables = array(
        'foo' => array('protected'=>false,'value'=>'bar'),
        'bar' => array('protected'=>true , 'value'=>'foo')
    );
}

$a = new Example;
$a->foo='a';
$a->bar ='b'; //throws an error