alamb commented on code in PR #9906:
URL: https://github.com/apache/arrow-datafusion/pull/9906#discussion_r1548544704
##########
datafusion-examples/examples/advanced_udwf.rs:
##########
@@ -75,6 +78,30 @@ impl WindowUDFImpl for SmoothItUdf {
Ok(DataType::Float64)
}
+ /// rewrite
+ fn simplify(
Review Comment:
This might be confusing as now this example UDWF will never call the actual
implementation.
Perhaps we can make a second UDWF and use it as an example of wrapping an
existing UDWF 🤔
##########
datafusion/expr/src/udwf.rs:
##########
@@ -266,6 +290,35 @@ pub trait WindowUDFImpl: Debug + Send + Sync {
fn aliases(&self) -> &[String] {
&[]
}
+
+ /// Optionally apply per-UDWF simplification / rewrite rules.
+ ///
+ /// This can be used to apply function specific simplification rules during
+ /// optimization. The default implementation does nothing.
+ ///
+ /// Note that DataFusion handles simplifying arguments and "constant
+ /// folding" (replacing a function call with constant arguments such as
+ /// `my_add(1,2) --> 3` ). Thus, there is no need to implement such
+ /// optimizations manually for specific UDFs.
+ ///
+ /// Example:
+ /// [`advanced_udwf.rs`]:
<https://github.com/apache/arrow-datafusion/blob/main/datafusion-examples/examples/advanced_udwf.rs>
+ ///
+ /// # Returns
+ /// [`ExprSimplifyResult`] indicating the result of the simplification NOTE
+ /// if the function cannot be simplified, the arguments *MUST* be returned
+ /// unmodified
+ fn simplify(
+ &self,
+ args: Vec<Expr>,
+ _partition_by: &[Expr],
Review Comment:
Ah this is interesting. I was trying to figure out how we would update this
signature to avoid a copy (for example, a rewrite would have to copy the
`order_by` exprs 🤔
I can't think of anything at the moment
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