Github user yjshen commented on a diff in the pull request:
https://github.com/apache/flink/pull/1916#discussion_r61378085
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/expressions/Expression.scala
---
@@ -17,13 +17,34 @@
*/
package org.apache.flink.api.table.expressions
-import java.util.concurrent.atomic.AtomicInteger
-
import org.apache.calcite.rex.RexNode
import org.apache.calcite.tools.RelBuilder
-abstract class Expression extends TreeNode[Expression] { self: Product =>
- def name: String = Expression.freshName("expression")
+import org.apache.flink.api.common.typeinfo.TypeInformation
+import org.apache.flink.api.table.trees.TreeNode
+import org.apache.flink.api.table.validate.ExprValidationResult
+
+abstract class Expression extends TreeNode[Expression] {
+ /**
+ * Returns the [[TypeInformation]] for evaluating this expression.
+ * It is sometimes available until the expression is valid.
+ */
+ def dataType: TypeInformation[_]
+
+ /**
+ * One pass validation of the expression tree in post order.
+ */
+ lazy val valid: Boolean = childrenValid && validateInput().isSuccess
+
+ def childrenValid: Boolean = children.forall(_.valid)
+
+ /**
+ * Check input data types, inputs number or other properties specified
by this expression.
+ * Return `ValidationSuccess` if it pass the check,
+ * or `ValidationFailure` with supplement message explaining the error.
+ * Note: we should only call this method until `childrenValidated ==
true`
--- End diff --
Ah, yes!
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