Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/20858#discussion_r176901348
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
---
@@ -699,3 +699,88 @@ abstract class TernaryExpression extends Expression {
* and Hive function wrappers.
*/
trait UserDefinedExpression
+
+/**
+ * The trait covers logic for performing null save evaluation and code
generation.
+ */
+trait NullSafeEvaluation extends Expression
+{
+ override def foldable: Boolean = children.forall(_.foldable)
+
+ override def nullable: Boolean = children.exists(_.nullable)
+
+ /**
+ * Default behavior of evaluation according to the default nullability
of NullSafeEvaluation.
+ * If a class utilizing NullSaveEvaluation override [[nullable]],
probably should also
+ * override this.
+ */
+ override def eval(input: InternalRow): Any =
+ {
--- End diff --
Spark usually use the style like:
```scala
override def eval(input: InternalRow): Any = {
val values = children.map(_.eval(input))
if (values.contains(null)) {
null
} else {
nullSafeEval(values)
}
}
```
You could follow the style of other codes.
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