alamb commented on issue #23814:
URL: https://github.com/apache/datafusion/issues/23814#issuecomment-5073565010

   > This all sounds right to me. Re. `apply_expressions`, most of the reasons 
for the [revert PR](https://github.com/apache/datafusion/pull/22437) are still 
true today
   > 
   > * the method isn't called from vanilla datafusion
   
   Yes -- I think we should figure out some way to fix this -- I can't imagine 
there is no way we can't refactor some of DataFusion to use the API so that it 
will 
   
   > * it cannot not have a default implementation, so every ExecutionPlan is 
forced to implement it
   
   Yes this is unfortunate but I don't see any way around it. It also moves us 
towards less downcasing (and thus more generic optimzer rules)
   
   > * it's tricky to implement because it involves tree node recursion and the 
behavior of the method can change often (ex. different expressions will be 
traversed depending on if its called before or after the filter pushdown 
optimizer pass
   
   I think it would make more sense if `apply_expressions` only walks the root 
of each expression (and any recursive tree walking is left to the caller if 
they want that)
   
   Perhaps we can handle this with appropriate documentation
   
   
   
   What I would suggest to make progress is finding some spot in the DataFusion 
code that could be rewritten to use apply_expressions
   


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