匿名类导致错误; $ var =新类[重复]

$gen = NEW CLASS {

    public function Num() {

        $number = mt_rand('0','9');

            function Duplicate($number) {
                $number = $number.$number;
                return $number;
            }

        return Duplicate($number);
    }

}

echo $gen->Num();

When running the code above I get the following error: Parse error: syntax error, unexpected 'echo' (T_ECHO) in /home/user/domain/new.php on line 69

Am I doing something wrong here?

And will this be backwards compatible with anything older than PHP 7?

</div>

You lack a semicolon before echo.