Tracking Issue for `Option::reduce`

[Qelxiros]

Feature gate: #![feature(option_reduce)]

This is a tracking issue for Option::reduce, which combines two Options into one if both are Some, otherwise choosing the one that's Some or returning None.

ACP: rust-lang/libs-team#609

Public API

impl<T> Option<T> {
    fn reduce<U, R, F>(self, other: Option<U>, f: F) -> Option<R>
    where
        T: Into<R>,
        U: Into<R>,
        F: FnOnce(T, U) -> R,
    {
        match (self, other) {
            (Some(a), Some(b)) => Some(f(a, b)),
            (Some(a), _) => Some(a.into()),
            (_, Some(b)) => Some(b.into()),
            _ => None,
        }
    }
}

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• Implementation: add Option::reduce #144274
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• Will this cause inference problems? ACP: Add Option::reduce libs-team#609 (comment)

Footnotes

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩

[Qelxiros]

@rustbot label -S-tracking-unimplemented

[camsteffen]

I just want to capture this note from the ACP:

During the call, our analysis was that this [more generic form using Into] would not cause undue inference problems (due to the FnOnce(T, U) -> R providing a constraint), but this is something we'll of course want to keep an eye out for while this is in nightly.

I also wonder if the conversion is a little too implicit. But this will be easier to answer after having some time to experiment.