Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/13084#discussion_r63116162
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
---
@@ -222,6 +222,33 @@ trait Unevaluable extends Expression {
/**
+ * An expression that gets replaced at runtime (currently by the
optimizer) into a different
+ * expression for evaluation. This is mainly used to provide compatibility
with other databases.
+ * For example, we use this to support "nvl" by replacing it with
"coalesce".
+ */
+trait RuntimeReplaceable extends Unevaluable {
+ /**
+ * Method for concrete implementations to override that specifies how to
construct the expression
+ * that should replace the current one.
+ */
+ def replaceForEvaluation(): Expression
+
+ /**
+ * Method for concrete implementations to override that specifies how to
coerce the input types.
+ */
+ def replaceForTypeCoercion(): Expression
--- End diff --
this is probably useful even outside RuntimeReplaceable, but I'm putting it
only here for now. If we make this more generic, we can trim quite a bit of our
type coercion code.
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at [email protected] or file a JIRA ticket
with INFRA.
---
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
