The AtomInteger trait is not needed for Atomic::fetch_update

[bruceg]

The function Atomic::fetch_update is only available for types that implement AtomInteger. However, it doesn't actually do any implicit integer operations like, say, fn fetch_add does — it explicitly leaves the update to a Rust closure that is restricted to safe operations on the data types. As such, the restriction is not needed, allowing fetch_update to be used on enum types, for example.

Here's my example that does not work with atomig as it is now:

#[derive(Atom, Copy)]
#[repr(u8)]
enum Enum {
    Off,
    On,
}

fn foo() {
    let t: Atomic<Enum> = Atomic::new(Enum::Off);
    t.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |t0| Some(match t0 {
        Enum::Off => Enum::On,
        Enum::On => Enum::Off,
    }));
}

[LukasKalbertodt]

Somehow I managed to unwatch my own repository 😲 I just now stumbled upon your comment by pure chance. Sorry for the delay!

The problem here is that fetch_update was not implemented for non-integer atomics in std for some time: rust-lang/rust#78639
This seems to be a simple oversight though. AtomicBool::fetch_update and AtomicPtr::fetch_update were already added and their stabilization hits stable with 1.53, in roughly three weeks. I will wait till then to properly fix this issue. I will let you know once I release the fix as 0.3.

[LukasKalbertodt]

I just released 0.3 which has fetch_update for all T: Atom available, not only for T: AtomInteger.

(Oh and don't mind the failing CI, that's just GitHub Actions not running Rust 1.53 yet.)

[bruceg]

Thanks