alamb commented on issue #22583:
URL: https://github.com/apache/datafusion/issues/22583#issuecomment-4565340290

   > I don't have a concrete idea here, but I do wonder whether this (and other 
"fast-path" optimizer work) is a symptom of an underlying problem -- it should 
be possible to express tree rewrites in a way where we shouldn't do any copies 
or tree manipulation if the rewrite doesn't fire.
   
   Yes -- I think the core primitive that is needed to express this is mutable 
tree rewrites -- now we either need to walk/copy the entire tree or else do two 
passes
   
   If we allowed mutations intead (aka `&mut`) in some cases we could do the 
walk and then rewrite in place if needed without forcing a copy
   
   @adriangb  did something like this for subqueries recently
   - https://github.com/apache/datafusion/pull/22298
   
   Maybe we can do soemthing similar here


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