关于 PHP 7.2 abstract function override 的使用

abstract class KeyManagerAbstract
{
    /**
     * 类似于
     *
     * return [
     *    self::UCC_USER_DETAIL => ["ucc:user:h:%d", 10],
     * ];
     *
     * @return array
     */
    abstract protected static function hashMap();
    public static function getHashKey(string $format, int $id)
    {
    }
}
class KeyManager extends KeyManagerAbstract
{
    protected static function hashMap()
    {
        // TODO: Implement hashMap() method.
    }
}

Fatal error: Can't inherit abstract function