rescript-lang/rescript-lang.org

Document co / contravariance (`<+a>`, `<-a>`)

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#149 opened on Jan 1, 2021

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Description

This one is definitely an advanced topic.

  • What does + and - mean?
  • What syntax constructs are possible? (type, function, etc.)
  • What practical use-cases does it have / Why do we need it?

Things to avoid:

  • Complex / too scientific wording
  • Too generic examples without practical context

Hints:

  • We use a covariant type in Js.Promise.t (see it here)

Contributor guide

Research direction
Write clear, non scientific explanations of covariance and contravariance using practical examples like Js.Promise.t. Avoid complex jargon and provide syntax constructs and use cases.
Tech stack
None
Domain
developer experience
Issue type
Documentation
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.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
None
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20