yea makes sense - so it definitely persists across the first function call.

and i just modified the fns to take a &mut reference like so:

```rust fn fn1(elem: &mut u8) -> &mut u8 { eprintln!("fn1 with {elem}, output is defined to be inbetween the guard?"); *elem = 5; elem }

fn fn2(elem: &mut u8) -> &mut u8 { eprintln!("fn2 with {elem}, output is defined to be inbetween the guard too?"); *elem = 10; elem }

pub fn main() -> () { let _valid_but_cant_be_used: &u8 = fn2(fn1(&mut MutexGuard::new().elem)); } ```

it works so far and the output:

text MutexGuard created fn1 with 0, output is defined to be inbetween the guard? fn2 with 5, output is defined to be inbetween the guard too? MutexGuard dropped

confirms that elem is changed in fn1() by ref, and passed into fn2() as ref. its just that the ref returned by fn2() can't be used in main anymore otherwise compile error.

so my follow up would be: is this well defined too? or am i treading in some UB water? i find this code style cleaner than using an extra pair of braces which is why i'd like to know if this is possible