runaurufu is not quite right, get_class_vars() does not return protected params, while this one does.

Thus it's extremely useful when having an abstract parent class and protected properties overriding in children.
For example, I use a class factory and one of the children has some static test methods that still need to output a paramether name, like $this->name, etc. With this example code, one can use static::getNotStaticProperty('name'), but not get_class_vars('name').

Try it:

trait static_reflector {
    /*
     * a purely static function that returns default properties of the non-static instance of the same class
     */
    static protected function getNonStaticProperty($key) {
        $me = get_class();
        $reflectionClass = new \ReflectionClass($me);
        $properties_list = $reflectionClass->getDefaultProperties();
        if (isset($properties_list[$key]))
            return $var_name = $properties_list[$key];
        else throw new RuntimeException("BUG: Unable to reflect non-static property '{$key}' from default properties of class {$me}");
    }
}

class a {

    use \static_reflector;

    protected $key_a = 'test ok';

    public static function test() {
        echo static::getNonStaticProperty('key_a')."\n";

        try {
            print static::getNonStaticProperty('key_b');
            echo "FAIL No exception thrown";
        } catch (RuntimeException $e) {
            echo "OK ".$e->getMessage();
        }

    }
}

echo get_class_vars('a')['key_a']; 
a::test();

this will return:
Notice: Undefined index: key_a in ...
test ok
OK BUG: Unable to reflect non-static property 'key_b' from default properties of class a

ps: Yes, this is copied from a unit test.

Worth noting that it will not return private parameters of parent class...
so it works exactly as get_class_vars or get_object_vars