Add drain_filter for BinaryHeap

[RalfJung]

std::collections::BinaryHeap is missing a drain_filter method (rust-lang/rfcs#2140).

[dtolnay]

Sounds good to me. I agree that this part of the API would be good to keep consistent between HashMap/HashSet and BTreeMap/BTreeSet. Please submit a PR.

[nbro]

An issue opened about 1 year ago. 17 thumbs up. Is this issue being addressed?

[Mark-Simulacrum]

I don't believe there's any current in-progress work, but we're happy to take PRs. If you're interested, we can probably connect you with a mentor or provide some instructions.

[nbro]

@Mark-Simulacrum Honestly, right now, I don't think I am qualified enough to address this issue. I would leave it someone else more qualified. Maybe, in the future, I may feel comfortable enough with Rust to address it.

[Ryan1729]

If someone ever gets around to this, it would be a shame to repeat the mistake of passing &T like in the Vec retain implementation. These methods should pass &mut T to the closure, like the HashMap implementation does.

[jq-rs]

@Mark-Simulacrum I could take a look to BtreeMap retain(), if there is some guidance/mentoring available. As a first Rust lang PR it may be otherwise a bit too steep effort.

[Mark-Simulacrum]

cc @rust-lang/libs would someone be able to provide some mentoring for @jq-rs?

[jq-rs]

Getting nowhere so far, so I'll pass this to future volunteers.

[jonhoo]

BinaryHeap now has drain, although for some reason it removes elements in arbitrary order (#59278) :/