Tracking Issue for {BTreeMap,BTreeSet}::retain

[mbrubeck]

This is a tracking issue for BTreeMap::retain and BTreeSet::retain (part of rust-lang/rfcs#1338).
The feature gate for the issue is #![feature(btree_retain)].

Unstable API

impl<T: Ord> BTreeSet<T> {
    pub fn retain<F>(&mut self, mut f: F) where F: FnMut(&T) -> bool;
}

impl<K: Ord, V> BTreeMap<K, V> {
    pub fn retain<F>(&mut self, mut f: F) where F: FnMut(&K, &mut V) -> bool;
}

Steps

• Implement the RFC
• FCP
• Adjust documentation
• Stabilization PR

Unresolved Questions

• Is the performance of the current implementation (based on drain_filter) good enough to be useful? Concern raised in this comment.

Implementation history

• Initial implementation: Implement BTreeMap::retain and BTreeSet::retain #79026

[joshtriplett]

We discussed this in today's @rust-lang/libs meeting. We'd like to see a comment added documenting the performance characteristics of this (as well as a corresponding update to drain_filter), and suggesting that this might not be what you want if you're removing a substantial number of elements.

Beyond that documentation, though, we'd be happy to see this stable.

@rfcbot merge

[rfcbot]

Team member @joshtriplett has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @sfackler

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.