typelevel / typelevel/cats

typeclass-based collections implementations

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enhancement help wanted
Dominant language
Scala
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Description

This is a recurring idea, most recently by @johnynek in https://github.com/typelevel/cats/pull/4118#issuecomment-1022714696.

i.e. we should work towards having a typeclass based implementation of HashSet, SortedSet, HashMap, SortedMap that use only typeclasses, not the instance methods.

Although the issue comes up in Cats since this is where we house instances for Scala stdlib, this might be a better PR for cats-collections.

Contributor guide

Open the contributing guide

First steps

  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

Start with the discussion linked from PR 4118, especially the referenced comment, and review how Cats currently houses Scala standard-library instances. Determine whether the work belongs in Cats or cats-collections, then define the scope for typeclass-based HashSet, SortedSet, HashMap, and SortedMap implementations. Done means the target repository and agreed implementation scope are established.

Written by the indexing model from the issue text.

Assessment

Tech stack
scala
Domain
data
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
20/100

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