[FLINK-20319] Improving the visitor pattern for operations

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 1.11.2
• Component/s: Table SQL / API
• Assignee: Unassigned
• Reporter: Ingo Bürk
• Created: 24/Nov/20 10:05
• Updated: 29/Apr/21 11:25

Description

The *OperationVisitor interfaces (which are not public API) don't always implement the visitor pattern correctly, and some things which would be useful are missing. Some things I discovered:

1. CatalogSinkModifyOperation doesn't accept() its child. It's likely that others have this problem as well, but I haven't checked further.
2. The base Operation interface doesn't have an accept() method at all. Potentially intentional since this interface actually is public API?
3. There's a catch-all QueryOperationVisitor#visit(QueryOperation other) that would be nice to split up into its subtypes (PlannerQueryOperation, …)