[hu3]

Still different. Yours only increments once. Doesn't pass basic QA.

And declaring a static variable inside a function, even if in main, smells.

[raggi]

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

[umanwizard]

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)]

[raggi]

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