sunjincheng121 edited a comment on issue #7664: [FLINK-11449][table] Uncouple the Expression class from RexNodes. URL: https://github.com/apache/flink/pull/7664#issuecomment-463961692 Hi @KurtYoung thank for you comments. In the long-term, we will only have one expression, but for now, I think we should complete the moudle refactoring of flink ASAP., and then merge Blink into Flink Master. The coexistence of Expression and PlannerExpression (the existing Expression has not changed) will greatly reduce the difficulty and workload of Blink merge. If I understand it correctly, Timo also proposed this approach in JIRA. Regarding to drop the existing CAST, ALIAS, EQUALTO etc., more than 100 function call definitions is a big change, and when merging the Blink, we will also need to do this kind of work which introduce extra huge overhead. Therefore, I prefer to add a thin layer of Expression abstraction to the API in the current PR. After the Blink has been merged, we can unify the Expression by adding an expression visitor, e.g.: `XXX extends ExpressionVisitor[RexNode]` which can translate an Expression to RexNode. In short, I expect to complete uncouple the Expression from RexNodes in the most efficient way to reduce the work of Blink merging. What do you think ?
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