Tracking Issue for BTreeMap::merge

Feature gate: #![feature(btree_merge)]

This is a tracking issue for rust-lang/libs-team#739

It adds a method similar to BTreeMap::append with merging two BTreeMaps in O(n + m) complexity, but allows the user to specify a callback function to handle what the resulting value should be for conflicting keys.

Public API

// use std::collections::BTreeMap; or use alloc::collections::btree_map; 

impl <K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
    pub fn merge(&mut self, other: BTreeMap<K, V, A>, conflict: impl FnMut(&K, V, V) -> V) { ... }
}

Steps / History

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

• ACP: rust-lang/libs-team#739
• Implementation:
  • #151981
  • #152418
• Optimization Issue: #153040
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• None yet.

Start with the BTreeMap::merge public API and feature gate btree_merge, then review implementation PRs #151981 and #152418 and optimization issue #153040. The tracking work is complete when the optimization, final comment period, and stabilization PR steps are resolved.