[GitHub] [spark] cloud-fan commented on a change in pull request #29798: [SPARK-32931][SQL] Unevaluable Expressions are not Foldable

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cloud-fan commented on a change in pull request #29798:
URL: https://github.com/apache/spark/pull/29798#discussion_r491801731



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
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@@ -318,7 +321,6 @@ trait Unevaluable extends Expression {
  */
 trait RuntimeReplaceable extends UnaryExpression with Unevaluable {
   override def nullable: Boolean = child.nullable
-  override def foldable: Boolean = child.foldable

Review comment:
       This change is noop in practice, because we replace `RuntimeReplaceable` at the beginning of the optimizer, so foldable or not doesn't really matter.
   
   Semantically, it might be clearer to just make `RuntimeReplaceable` a pure delegator like `Alias`, but it complicates the expression tree. Anyway, this is out of the scope of this PR.




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