OP you keep comparing to doesn't even declare the variable. I'm done with you.

OP here, not showing how to declare the variable was an oversight on my part.

  static mut COUNTER: u32 = 0;

(at top-level)

If on 2024 edition, you will additionally need

  #![allow(static_mut_refs)]

Yup, your example was fine, as I said I just wanted to show a safe method too :-)