PHP String reversal without using extra memory

Question

How can i reverse $str= "hello\n" to "olleh\n" without using any extra memory variable?

I looked up for prebuilt functions but they all use memory, also, i think string is immutable so basically can this be done without any tweak or creating a new string is the only option?

Answer 1

I don't think anything is immutable in PHP. So

$str = strrev($str);

may be of some use.

Fear the micro-optimization as it will take all your time, for no real result ! :)