simplify returns closure

datafusion-examples/examples/simplify_udaf_expression.rs

@@ -17,7 +17,7 @@
 
 use arrow_schema::{Field, Schema};
 use datafusion::{arrow::datatypes::DataType, logical_expr::Volatility};
-use datafusion_common::tree_node::Transformed;
+use datafusion_expr::function::AggregateFunctionSimplification;
 use datafusion_expr::simplify::SimplifyInfo;
 
 use std::{any::Any, sync::Arc};
@@ -88,27 +88,26 @@ impl AggregateUDFImpl for BetterAvgUdaf {
     }
     // we override method, to return new expression which would substitute
     // user defined function call
-    fn simplify(
-        &self,
-        aggregate_function: AggregateFunction,
-        _info: &dyn SimplifyInfo,
-    ) -> Result<Transformed<Expr>> {
+    fn simplify(&self) -> Option<AggregateFunctionSimplification> {
         // as an example for this functionality we replace UDF function
         // with build-in aggregate function to illustrate the use
-        let expr = Expr::AggregateFunction(AggregateFunction {
-            func_def: AggregateFunctionDefinition::BuiltIn(
-                // yes it is the same Avg, `BetterAvgUdaf` was just a
-                // marketing pitch :)
-                datafusion_expr::aggregate_function::AggregateFunction::Avg,
-            ),
-            args: aggregate_function.args,
-            distinct: aggregate_function.distinct,
-            filter: aggregate_function.filter,
-            order_by: aggregate_function.order_by,
-            null_treatment: aggregate_function.null_treatment,
-        });
-
-        Ok(Transformed::yes(expr))
+        let simplify = |aggregate_function: datafusion_expr::expr::AggregateFunction,
+                        _: &dyn SimplifyInfo| {
+            Ok(Expr::AggregateFunction(AggregateFunction {
+                func_def: AggregateFunctionDefinition::BuiltIn(
+                    // yes it is the same Avg, `BetterAvgUdaf` was just a
+                    // marketing pitch :)
+                    datafusion_expr::aggregate_function::AggregateFunction::Avg,
+                ),
+                args: aggregate_function.args,
+                distinct: aggregate_function.distinct,
+                filter: aggregate_function.filter,
+                order_by: aggregate_function.order_by,
+                null_treatment: aggregate_function.null_treatment,
+            }))
+        };
+
+        Some(Box::new(simplify))
     }
 }
 

datafusion/expr/src/function.rs

@@ -97,3 +97,16 @@ pub type PartitionEvaluatorFactory =
 /// its state, given its return datatype.
 pub type StateTypeFunction =
     Arc<dyn Fn(&DataType) -> Result<Arc<Vec<DataType>>> + Send + Sync>;
+
+/// [crate::udaf::AggregateUDFImpl::simplify] simplifier closure
+/// A closure with two arguments:
+/// * 'aggregate_function': [crate::expr::AggregateFunction] for which simplified has been invoked
+/// * 'info': [crate::simplify::SimplifyInfo]
+///
+/// closure returns simplified [Expr] or an error.
+pub type AggregateFunctionSimplification = Box<
+    dyn Fn(
+        crate::expr::AggregateFunction,
+        &dyn crate::simplify::SimplifyInfo,
+    ) -> Result<Expr>,
+>;

datafusion/expr/src/udaf.rs

@@ -17,15 +17,12 @@
 
 //! [`AggregateUDF`]: User Defined Aggregate Functions
 
-use crate::expr::AggregateFunction;
-use crate::function::AccumulatorArgs;
+use crate::function::{AccumulatorArgs, AggregateFunctionSimplification};
 use crate::groups_accumulator::GroupsAccumulator;
-use crate::simplify::SimplifyInfo;
 use crate::utils::format_state_name;
 use crate::{Accumulator, Expr};
 use crate::{AccumulatorFactoryFunction, ReturnTypeFunction, Signature};
 use arrow::datatypes::{DataType, Field};
-use datafusion_common::tree_node::Transformed;
 use datafusion_common::{not_impl_err, Result};
 use std::any::Any;
 use std::fmt::{self, Debug, Formatter};
@@ -201,12 +198,8 @@ impl AggregateUDF {
     /// Do the function rewrite
     ///
     /// See [`AggregateUDFImpl::simplify`] for more details.
-    pub fn simplify(
-        &self,
-        aggregate_function: AggregateFunction,
-        info: &dyn SimplifyInfo,
-    ) -> Result<Transformed<Expr>> {
-        self.inner.simplify(aggregate_function, info)
+    pub fn simplify(&self) -> Option<AggregateFunctionSimplification> {
+        self.inner.simplify()
     }
 }
 
@@ -368,7 +361,7 @@ pub trait AggregateUDFImpl: Debug + Send + Sync {
         &[]
     }
 
-    /// Optionally apply per-UDF simplification / rewrite rules.
+    /// Optionally apply per-UDaF simplification / rewrite rules.
     ///
     /// This can be used to apply function specific simplification rules during
     /// optimization (e.g. `arrow_cast` --> `Expr::Cast`). The default
@@ -379,22 +372,18 @@ pub trait AggregateUDFImpl: Debug + Send + Sync {
     /// `my_add(1,2) --> 3` ). Thus, there is no need to implement such
     /// optimizations manually for specific UDFs.
     ///
-    /// # Arguments
-    /// * 'aggregate_function': Aggregate function to be simplified
-    /// * 'info': Simplification information
-    ///
     /// # Returns
-    /// [`Transformed`] indicating the result of the simplification NOTE
-    /// if the function cannot be simplified, [Expr::AggregateFunction] with unmodified [AggregateFunction]
-    /// should be returned
-    fn simplify(
-        &self,
-        aggregate_function: AggregateFunction,
-        _info: &dyn SimplifyInfo,
-    ) -> Result<Transformed<Expr>> {
-        Ok(Transformed::yes(Expr::AggregateFunction(
-            aggregate_function,
-        )))
+    ///
+    /// [None] if simplify is not defined or,
+    ///
+    /// Or, a closure with two arguments:
+    /// * 'aggregate_function': [crate::expr::AggregateFunction] for which simplified has been invoked
+    /// * 'info': [crate::simplify::SimplifyInfo]
+    ///
+    /// closure returns simplified [Expr] or an error.
+    ///
+    fn simplify(&self) -> Option<AggregateFunctionSimplification> {
+        None
     }
 }
 

datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs

@@ -1385,14 +1385,12 @@ impl<'a, S: SimplifyInfo> TreeNodeRewriter for Simplifier<'a, S> {
             Expr::AggregateFunction(datafusion_expr::expr::AggregateFunction {
                 func_def: AggregateFunctionDefinition::UDF(ref udaf),
                 ..
-            }) => {
-                let udaf = udaf.clone();
-                if let Expr::AggregateFunction(aggregate_function) = expr {
-                    udaf.simplify(aggregate_function, info)?
-                } else {
-                    unreachable!("this branch should be unreachable")
+            }) => match (udaf.simplify(), expr) {
+                (Some(simplify_function), Expr::AggregateFunction(af)) => {
+                    Transformed::yes(simplify_function(af, info)?)
                 }
-            }
+                (_, expr) => Transformed::no(expr),
+            },
 
             //
             // Rules for Between
@@ -1760,7 +1758,9 @@ fn inlist_except(mut l1: InList, l2: InList) -> Result<Expr> {
 #[cfg(test)]
 mod tests {
     use datafusion_common::{assert_contains, DFSchemaRef, ToDFSchema};
-    use datafusion_expr::{interval_arithmetic::Interval, *};
+    use datafusion_expr::{
+        function::AggregateFunctionSimplification, interval_arithmetic::Interval, *,
+    };
     use std::{
         collections::HashMap,
         ops::{BitAnd, BitOr, BitXor},
@@ -3791,15 +3791,11 @@ mod tests {
             unimplemented!("not needed for testing")
         }
 
-        fn simplify(
-            &self,
-            aggregate_function: datafusion_expr::expr::AggregateFunction,
-            _info: &dyn SimplifyInfo,
-        ) -> Result<Transformed<Expr>> {
+        fn simplify(&self) -> Option<AggregateFunctionSimplification> {
             if self.simplify {
-                Ok(Transformed::yes(col("result_column")))
+                Some(Box::new(|_, _| Ok(col("result_column"))))
             } else {
-                Ok(Transformed::no(Expr::AggregateFunction(aggregate_function)))
+                None
             }
         }
     }