Tracking Issue for OneSidedRange

[cramertj]

The feature gate for the issue is #![feature(one_sided_range)], introduced in #62282.

[KodrAus]

Since the linked implementation PR was closed (just from inactivity) we don't really have a feature to track here yet. I'll go ahead and close this one now, but if #62282 resurfaces in the future we can re-open this!

[its-the-shrimp]

Should this be reopened now that OneSidedRange is on nightly? No clue when it got there, but it is most definitely there, my eyes don't deceive me

https://doc.rust-lang.org/std/ops/trait.OneSidedRange.html

[its-the-shrimp]

Also, should this trait be unsafe? Since the guarantee of

must return Bound::Unbounded from one of RangeBounds::start_bound or RangeBounds::end_bound.

Can't be represented by this trait directly (in its current form at least)

Making it unsafe will allow for the following use of it:

fn f<T>(x: impl OneSidedRange<T>) {
    match (x.start_bound(), x.end_bound()) {
        (start, Bound::Unbounded) => todo!(),
        (Bound::Unbounded, end) => todo!(),
        _ => unsafe { // Safety: guaranteed by `OneSidedRange`
            std::hint::unreachable_unchecked()
        }
    }
}

Another possibility is the following API for this trait:

enum OnlyBound<T> {
    Start(Bound<T>),
    End(Bound<T>),
}

trait OneSidedRange<T>: RangeBounds<T> {
    fn bound(&self) -> OnlyBound<T> {
        match (self.start_bound(), self.end_bound()) {
            (start, Bound::Unbounded) => OnlyBound::Start(start),
            (Bound::Unbounded, end) => OnlyBound::End(end),
            _ => unreachable!(),
        }
    }
}