feat: make Equatable abstract mixin class

[utamori]

Status

READY

Breaking Changes

NO

Description

Make Equatable class an abstract mixin class so that it can be used as a mixin

Related PRs

no

Todos

• Tests
• Documentation
• Examples

Steps to Test or Reproduce

Outline the steps to test or reproduce the PR here.

dart test

Impact to Remaining Code Base

This PR will affect:

• Probably not.

[shilangyu]

@felangel what are your thoughts?

[shilangyu]

This is a breaking change, so I think we could remove EquatableMixin all together and mark this as release v3?

[shilangyu]

As per my issue, I still doubt that this should be a class at all. This works perfectly fine as a mixin-only, so I see no reason as to why would anyone extend it instead of mixin it in.

[felangel]

It would be quite inconvenient for existing apps if we forced them to refactor all classes to use equatable as a mixin imo

[shilangyu]

fair enough, for sake of compatibility it makes sense. In the long run though (and since it is a breaking change anyways) I don't see value in it being a class.

[utamori]

I didn't explain myself well enough: an abstract mixin class can be extends equally well as an abstract class.
Users can update it without change their code.

https://dart.dev/language/modifier-reference

[ricardodalarme]

@felangel even in a large project, this change should be easy to make, a simple search and replace can do 95% of the work, plus people can choose to update the version or not.

[felangel]

This is still a breaking change because even as a mixin class you won't be able to use Equatable in cases like this:

[felangel]

This change is still a breaking change and I don't think it's worth it especially considering I'm planning to make the next major version of equatable use macros instead so you'd always just annotate your class with @Equatable and that's it (no more props 🎉)

@Equatable()
class Person {
  const Person({required this.name});
  final String name;
}

See also https://github.com/felangel/data_class which will be built on top of the equatable macro so you could go a few steps further:

@Data()
class Person {
  final String name;
}

[felangel]

Closing for now based on my above comment, thanks so much for the contribution though -- I really appreciate it!