jayzhan211 commented on code in PR #10214:
URL: https://github.com/apache/datafusion/pull/10214#discussion_r1577889091
##########
datafusion/expr/src/udaf.rs:
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@@ -354,6 +360,24 @@ pub trait AggregateUDFImpl: Debug + Send + Sync {
fn aliases(&self) -> &[String] {
&[]
}
+
+ /// Construct an expression that calculates the aggregate in reverse.
+ /// Typically the "reverse" expression is itself (e.g. SUM, COUNT).
+ /// For aggregates that do not support calculation in reverse,
+ /// returns None (which is the default value).
+ fn reverse_expr(&self) -> ReversedExpr {
Review Comment:
I tried to take the owned type, but
```
function arguments must have a statically known size, borrowed types always
have a known size: `&`
```
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