enum Expr extension on logical level

[bertvermeiren]

Hi,

In order to write some additional logical and physical plan implementations, we do have to create some kind of "composite" logical expression.

Nowadays in the code base you have already existing expression implementations with such composite behaviour like the ScalarFunction expression containing other expressions (the arguments) ; the AggregateFunction containing filtering and order by expressions, etc.

Lot's of interfaces/API/traits are working on the enum Expr directly :

UserLogicalNode::with_exprs_and_inputs and related UserLogicalNode::expressions
Applying optimisation rules on those logical plans by analysing and potentially rewriting expressions.

By not having some customisation, we loose the internal semantics of “composite” logical expressions if those have to be “decomposed” again into existing expression implementations to be used throughout the codebase.

Would it be opportune the have an extension point on logical expression as well, like it has been introduced on the LogicalPlan::Extension(Extension)?

What are the opinions on this ? Are there other alternatives ? How would such an extension look like ?

Regards, Bert.