chenkovsky commented on code in PR #17220:
URL: https://github.com/apache/datafusion/pull/17220#discussion_r2297761959
##########
datafusion/expr/src/udf.rs:
##########
@@ -714,6 +774,58 @@ pub trait ScalarUDFImpl: Debug + DynEq + DynHash + Send +
Sync {
fn documentation(&self) -> Option<&Documentation> {
None
}
+
+ /// Attempts to optimize or transform the function call.
+ ///
+ /// This method allows UDF implementations to provide optimized versions
+ /// of function calls or transform them into different expressions.
+ /// Returns `None` if no optimization is available.
+ ///
+ /// # Arguments
+ /// * `_args` - The function arguments to potentially optimize
+ ///
+ /// # Returns
+ /// An optional optimized expression, or None if no optimization is
available
+ fn try_call(&self, _args: &[Expr]) -> Result<Option<Expr>> {
+ Ok(None)
+ }
+
+ /// Plans the scalar UDF implementation with lambda function support.
+ ///
+ /// This method enables UDF implementations to work with lambda functions
+ /// by allowing them to plan and prepare lambda expressions for execution.
+ /// Returns a new implementation instance if lambda planning is needed.
+ ///
+ /// # Arguments
+ /// * `_planner` - The lambda planner for converting logical lambdas to
physical
+ /// * `_args` - The function arguments that may include lambda expressions
+ /// * `_input_dfschema` - The input schema context for lambda planning
+ ///
+ /// # Returns
+ /// An optional new UDF implementation with planned lambdas, or None if no
planning is needed
+ fn plan(
+ &self,
+ _planner: &dyn LambdaPlanner,
+ _args: &[Expr],
+ _input_dfschema: &DFSchema,
+ ) -> Result<Option<Arc<dyn ScalarUDFImpl>>> {
+ Ok(None)
+ }
Review Comment:
I considered your solutions before. but they all require a significant
change. this solution is not the perfect one. But I think it's the least
modification one.
Lambda functions are just a seasoning; although they are indispensable, most
UDFs do not require them. For example, in Databricks, only the following
functions use lambda functions:
aggregate,array_sort,exists,filter,forall,map_filter,map_zip_with,transform,transform_keys,transform_values,zip_with.
Therefore, I feel there is no need for us to make huge changes just because
of this. That's why I selected the least modification one.
> It requires users to call this function beforehand for the higher-order
function to actually work.
it's a currying. from my side, this is not hard to understand.
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