alamb commented on issue #2535:
URL:
https://github.com/apache/arrow-datafusion/issues/2535#issuecomment-1135932491
I think it is important for expression simplification that expressions can
be partially evaluated at optimization time.
In terms of evaluating on logical plan `Expr`s directly, I agree there is no
theoretical reason this can not be done, but if we did so it will result in
dual expression evaluation systems that would have be kept in sync. This might
be especially hard if someone wanted to use a different physical expression
evaluation system
I understand the desire to remove the direct code dependence on the
execution engine from the optimizer -- perhaps we can do so via a trait -- for
example, we could pass some sort of `dyn ExprEvaluator` to the optimizer for
use in `simplify expressions` and elsewhere.
By default, DataFusion could provide the evaluator based on `PhysicalExpr`
-- and for those users of the optimizer itself they could decide the most
appropriate way to provide expression evaluation to the optimizer
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