$var = Carbon::parse( 10 10 2000 );
$var->addDays(10);
echo $var;
$var2 = $var->->addDays(10);
echo $var;
We also provide CarbonImmutable class extending DateTimeImmutable. The same methods are available on both classes but when you use a modifier on a Carbon instance, it modifies and returns the same instance, when you use it on CarbonImmutable, it returns a new instances with the new value.
https://carbon.nesbot.com/docs/