src/Container/CompositeServiceFactory.php
private function extended(callable $previous = null, callable $current): callable
    {
        return is_null($previous) ? $current : new Extension($current, $previous);
    }
private function extended(callable $previous = null, callable $current): callable
    {
        return is_null($previous) ? $current : new Extension($current, $previous);
    }
private function extended ( callable $ previous = null , callable $ current ) : callable { return is_null ( $ previous ) ? $ current : new Extension ( $ current , $ previous ) ; }
Return the previous service factory extended with the current service
factory.

@param callable $previous
@param callable $current
@return callable
Return the previous service factory extended with the current service factory .