typelevel/cats

typeclass-based collections implementations

Open

#4,147 opened on Mar 9, 2022

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 (28 comments) (2 reactions) (0 assignees)Scala (5,438 stars) (1,241 forks)batch import
enhancementhelp wanted

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

Tech stack
None
Domain
data
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
basic understanding of cats typeclassesfamiliarity with Scala collectionsknowledge of cats collections
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
Start by reading the referenced comment in PR #4118 for context. Then, explore the cats collections repository to understand its structure and consider how to implement typeclass based collections using cats' Hash and Order typeclasses. The issue suggests this may be a better fit for cats collections, so focus on that repository. Review any existing discussions or attempts in the cats collections issues.