peter-toth opened a new pull request, #13467:
URL: https://github.com/apache/datafusion/pull/13467

   ## Which issue does this PR close?
   
   Part of https://github.com/apache/datafusion/issues/8913.
   
   ## Rationale for this change
   
   The current implementation of `LogicalPlan:apply_children()`, 
`LogicalPlan::map_children()`, `LogicalPlan::apply_expressions()`, 
`LogicalPlan::map_expressions()`, `Expr::apply_children()` and 
`Expr::map_children()` are confusing due the `map_until_stop_and_collect` 
macro. I think we can introduce a trait that can contain sibling arbitrary 
elements that can be applied on and mapped:
   ```
   /// [`Container`] contains elements that a function can be applied on or 
mapped. The
   /// elements of the container are siblings so the continuation rules are 
similar to
   /// [`TreeNodeRecursion::visit_sibling`] / 
[`Transformed::transform_sibling`].
   pub trait Container<'a, T: 'a>: Sized {
       fn apply_elements<F: FnMut(&'a T) -> Result<TreeNodeRecursion>>(
           &'a self,
           f: F,
       ) -> Result<TreeNodeRecursion>;
   
       fn map_elements<F: FnMut(T) -> Result<Transformed<T>>>(
           self,
           f: F,
       ) -> Result<Transformed<Self>>;
   }
   ```
   
   ## What changes are included in this PR?
   
   This PR:
   - Gets rid of `map_until_stop_and_collect` macro.
   - Adds the `Container` trait and blanket implementations for `Box`, 
`Option`, `Vec`, tuples, ...
   - Defined the `Container` implementation for `Expr` and `LogicalPlan`.
   - Simplifies the above mentioned `apply...` and `map...` methods.
   
   ## Are these changes tested?
   
   Yes, with exitsing UTs.
   
   ## Are there any user-facing changes?
   
   No.
   


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