typelevel / typelevel/cats

Proposal to add Validated.ensureA[EE >: E, B](A => Validated[EE, B]): Validated[EE, A]

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Dominant language
Scala
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Description

I sometimes find that I want to run a post-construction verification using validated. The tools that are currently there are:

  • Validated.andThen which requires you to provide a new success even though I want to keep the value I already posess.
  • Validated.ensure in which you can't report more than one failure in one go.

So I wanted to propose a method:

Validated#ensureA[EE >: E, B](check: A => Validated[EE, B]): Validated[EE, A]

that will let run an arbitrary number of post verification steps keeping the original value A in one go.

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 at the Validated API and read the existing andThen and ensure methods, which the proposal identifies as related behavior. Confirm how a post-construction check can retain the original value while combining validation results; done means the proposed ensureA signature and behavior are covered by tests.

Written by the indexing model from the issue text.

Assessment

Tech stack
scala
Domain
backend-api-design
Issue type
Feature
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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