PHP实现类似final的功能

[php]代码库

class a {
        public $attr = 'a'; 
        private $attr1 = 'b';
    }

    class b extends a {
        public $attr = 'b';
        public function __construct(){
            $pvars = get_class_vars(get_parent_class($this) );
            $cvars = get_class_vars(get_class($this));
            $inter = array_intersect_key($pvars,$cvars); 
            if(!empty($inter)) {
                throw new Exception("Can't declare parent's attribute!");
            }
        }

    }

    try{
        $a = new b();
    } catch (Exception $e) {
        echo $e->getMessage();
    }