Mutation: Optimistic updates

[snapsl]

How to implement optimistic updates with Riverpod mutations?

[rrousselGit]

final prevState = state;
try {
  state = <your optimistic update>

  return await repo.post();
} catch (err) {
  state = prevState;
}

[snapsl]

Ops. I should have thought of that myself. 😅
This could be added to the docs.

Perhaps this could be automated so that Riverpod restores the previous state in the event of a mutation.error?

[rrousselGit]

We certainly could have a @Mutation(optimistic: true) or something

[rrousselGit]

The main challenge is that we can only automate it for immutable state.

And there's also the addec challenge of "what if the state changed in the meantime". Reverting it could revert more than needed.
But it could possibly be combined with #3887

[snapsl]

I do believe that this should be the default setting, because if an update is not optimistic, this would result in a noop.
Yeah, scheduling of async mutation could get a problem.

[rrousselGit]

I don't think that should be the default.

But about race conditions, we could throw if the state is mutated outside of the mutation while the optimistic mutation is pending.
I'll think about it.