mutable.MultiMap cannot be used as documented without warnings

[raboof]

The mutable.MultiMap docs suggest val mm = new HashMap[Int, Set[String]] with MultiMap[Int, String], but HashMap is marked @deprecatedInheritance("HashMap wil be made final; use .withDefault for the common use case of computing a default value", "2.13.0").

[lrytz]

Should MultiMap be deprecated? @szeiger / @julienrf

[julienrf]

Probably, but we should provide a proper replacement.

[lrytz]

Would it be enought to point people to scala-collection-contrib? Is it planned to release that module?

[julienrf]

We need to make this repository “releasable”, and then to find someone who wants to take the responsibility of pushing git tags to cut releases.

[szeiger]

We could provide a factory method that gives you a MultiMap for a HashMap typed as Map with MultiMap. It could still be implemented as a wrapper (similar to MultiDict) when HashMap is made final.

But I would prefer to deprecate MultiMap instead. I'm not sure we should point to MultiDict as a recommended replacement at this point. After all, if we were sufficiently confident that the API is good and can be kept stable we should have added it to the standard library. We could recommend a simple Map as a replacement (and point to MultiDict as another option). After all, MultiMap does not add much functionality on top of Map.

[szeiger]

The PR targets 2.13.1. Since deprecation is the most likely solution (and the current implementation works fine, albeit with a deprecation warning) I'm rescheduling this to 2.13.1.