rust-lang / rust-lang/rfcs

Set-based operations on HashMap

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Description

HashSet has all kinds of useful set functionality, but these functions are incompatible with HashMap keys:

  • difference
  • symmetric_difference
  • intersection
  • union
  • is_disjoint
  • is_subset
  • is_superset

It would be nice to enable the use of these functions between HashMaps and HashSets, either by allowing semi-cheap conversions from HashMap.keys to HashSet or by enabling those functions to take either maps or sets.

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  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Review the listed HashSet operations alongside HashMap.keys and the proposed conversion or shared-operation approaches. Done means the listed set operations have an agreed API for use between HashMaps and HashSets, with coverage for the supported combinations.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
backend-api-design
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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