JsObject should return immutable collections (play-json 2.8/ scala 2.13)

[987Nabil]

I was just migrating to scala 2.13 and realised, that the only collections related migration I had to do, was with JsObject. I was using this two fields

  /**
   * The fields of this JsObject in the order passed to the constructor
   */
  lazy val fields: collection.Seq[(String, JsValue)] = underlying.toSeq

  /**
   * The value of this JsObject as an immutable map.
   */
  lazy val value: Map[String, JsValue] = underlying match {
    case m: immutable.Map[String, JsValue] => m
    case m                                 => m.toMap
  }

What I found interesting is, that even the second comment says immutable map and underlying.toSeq is returning an immutable.Seq the return values are collection.Mapand collection.Seq. This seems odd to me. Especially because immutable collections should be considered the default, since it is what is defined in predef now (2.13).

Are there any good reasons to not change this to immutable?

[987Nabil]

After checking out play json, I realized that underlying.toSeq is not returning an immutable collection.
But values for sure is always immutable and I don't see any harm in the type being more restrictive/concrete.

So my suggestion would be

  /**
   * The value of this JsObject as an immutable map.
   */
  lazy val value: immutable.Map[String, JsValue] = underlying match {
    case m: immutable.Map[String, JsValue] => m
    case m                                 => m.toMap
  }

  /**
   * Return all fields as a set
   */
  def fieldSet: immutable.Set[(String, JsValue)] = fields.toSet

[octonato]

This is a backwards-incompatible change. The way to go here is to add new variants that are immutable and deprecate the mutable ones.

So, ok for fieldSet. But value must stay what it is and instead we need a new variant, eg: valueMap or asMap.

valueMap aligns well with fieldSet

[octonato]

@14mr0n, forgot to mention. PRs are super welcome! 😉

[987Nabil]

@renatocaval thanks for clarification. I'll happily do this changes and open a PR in the next days. :)

[asazernik]

I might also jump on this when/if my workload permits.

[RichardMarto]

Any updates on this issue? I'm able to fix it right now if needed.

[octonato]

@RichardMarto no updates and I don't think anyone is working on it. Feel free to pick.

Let me know if you do it so I assign to you just to signal to others that someone is already on it.

[RichardMarto]

I'm just not sure about which version should be in since argument on @deprecated(message: String, since: String), should I use the next minor version? Where can I find more about how this project is versioned?

[RichardMarto]

Is there any documentation that needs to be updated?
The tests that already exist should be enough for these changes, right?
Was I right to assume 2.9.3 as the version in which value will be deprecated?

[RichardMarto]

I think I misunderstood something. fieldSet should be ignored, deprecated or just changed?
I thought that it should be changed, but it was also a backward-incompatible change.

[johnduffell]

This also affects JsError and other in this file due to this import, would be great to have it fixed:

play-json/play-json/shared/src/main/scala/play/api/libs/json/JsResult.scala

Line 7 in f1769bd

import scala.collection.Seq