[SPARK-24305][SQL][FOLLOWUP] A small optimization of Slice and Elemen…

…tAt expression

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala

@@ -1596,7 +1596,7 @@ case class Slice(x: Expression, start: Expression, length: Expression)
 
   override def inputTypes: Seq[AbstractDataType] = Seq(ArrayType, IntegerType, IntegerType)
 
-  override def children: Seq[Expression] = Seq(x, start, length)
+  @transient override lazy val children: Seq[Expression] = Seq(x, start, length) // called from eval
 
   @transient private lazy val elementType: DataType = x.dataType.asInstanceOf[ArrayType].elementType
 
@@ -2092,8 +2092,11 @@ case class ArrayPosition(left: Expression, right: Expression)
   since = "2.4.0")
 case class ElementAt(left: Expression, right: Expression) extends GetMapValueUtil {
 
-  @transient private lazy val ordering: Ordering[Any] =
-    TypeUtils.getInterpretedOrdering(left.dataType.asInstanceOf[MapType].keyType)
+  @transient private lazy val mapKeyType = left.dataType.asInstanceOf[MapType].keyType
+
+  @transient private lazy val arrayContainsNull = left.dataType.asInstanceOf[ArrayType].containsNull
+
+  @transient private lazy val ordering: Ordering[Any] = TypeUtils.getInterpretedOrdering(mapKeyType)
 
   @transient override lazy val dataType: DataType = left.dataType match {
     case ArrayType(elementType, _) => elementType
@@ -2104,7 +2107,7 @@ case class ElementAt(left: Expression, right: Expression) extends GetMapValueUti
     Seq(TypeCollection(ArrayType, MapType),
       left.dataType match {
         case _: ArrayType => IntegerType
-        case _: MapType => left.dataType.asInstanceOf[MapType].keyType
+        case _: MapType => mapKeyType
         case _ => AnyDataType // no match for a wrong 'left' expression type
       }
     )
@@ -2114,8 +2117,7 @@ case class ElementAt(left: Expression, right: Expression) extends GetMapValueUti
     super.checkInputDataTypes() match {
       case f: TypeCheckResult.TypeCheckFailure => f
       case TypeCheckResult.TypeCheckSuccess if left.dataType.isInstanceOf[MapType] =>
-        TypeUtils.checkForOrderingExpr(
-          left.dataType.asInstanceOf[MapType].keyType, s"function $prettyName")
+        TypeUtils.checkForOrderingExpr(mapKeyType, s"function $prettyName")
       case TypeCheckResult.TypeCheckSuccess => TypeCheckResult.TypeCheckSuccess
     }
   }
@@ -2137,14 +2139,14 @@ case class ElementAt(left: Expression, right: Expression) extends GetMapValueUti
           } else {
             array.numElements() + index
           }
-          if (left.dataType.asInstanceOf[ArrayType].containsNull && array.isNullAt(idx)) {
+          if (arrayContainsNull && array.isNullAt(idx)) {
             null
           } else {
             array.get(idx, dataType)
           }
         }
       case _: MapType =>
-        getValueEval(value, ordinal, left.dataType.asInstanceOf[MapType].keyType, ordering)
+        getValueEval(value, ordinal, mapKeyType, ordering)
     }
   }
 
@@ -2153,7 +2155,7 @@ case class ElementAt(left: Expression, right: Expression) extends GetMapValueUti
       case _: ArrayType =>
         nullSafeCodeGen(ctx, ev, (eval1, eval2) => {
           val index = ctx.freshName("elementAtIndex")
-          val nullCheck = if (left.dataType.asInstanceOf[ArrayType].containsNull) {
+          val nullCheck = if (arrayContainsNull) {
             s"""
                |if ($eval1.isNullAt($index)) {
                |  ${ev.isNull} = true;