Peter Toth

@ozankabak, please let me know your thoughts on the above. Do you think it is ok to add `TreeNodeRecursion::Stop` support and make `TreeNodeRewriter` symmetric in a follow-up PR?

> I don't think we should make two API changes. @berkaysynnada will do some exploring and collaborate with you to get this PR to the finish line Actually, I plan...

> I think there are good natural boundaries here. We can think about the `Transformed` usage and the `TreeNodeRecursion` enum in one PR (this one), and then think about the...

> I would like to review and collaborate on this PR. Could you please notify me when it is ready? Sure, let me get back to you today or tomorrow....

> UPDATE: It looks like Expr already derives Hash. Is there a reason we're not using that instead of string keys? I forgot to comment on this thread that my...

@alamb, I think you shouldn't wait for my https://github.com/apache/datafusion/pull/10473, as there is still some preliminary work required I need to finish (https://github.com/apache/datafusion/pull/10543) and I'm still not sure about a few...

I'm happy to take this.

> Are there any potential issues with simply using the existing `Hash` implementation of `Expr` to create `HashSet`s? > > Serveral other optimization passes use string names as keys for...

> I like the idea of generalizing the `(u64, &Expr)` struct into something reuseable across optimizations. Honestly, I don't know those referenced usecases, but I feel `(u64, &Expr)` (and any...

I've opened a draft PR: https://github.com/apache/datafusion/pull/10473 and will try to wrap it up in the following days.