update classdoc for WithField explaining why we extend Unevaluable

apache · Aug 12, 2020 · 2b0ac34 · 2b0ac34
1 parent 977ff31
commit 2b0ac34
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/...atalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeCreator.scala b/...atalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeCreator.scala
@@ -556,6 +556,9 @@ trait StructFieldsOperation {
 
 /**
  * Add or replace a field by name.
+ *
+ * We extend [[Unevaluable]] here to ensure that [[UpdateFields]] can include it as part of its
+ * children, and thereby enable the analyzer to resolve and transform valExpr as necessary.
  */
 case class WithField(name: String, valExpr: Expression)
   extends Unevaluable with StructFieldsOperation {