ARROW-9756: [Rust] [DataFusion] Added support for scalar UDFs of arbitrary return types

rust/datafusion/README.md

@@ -53,6 +53,8 @@ DataFusion includes a simple command-line interactive SQL utility. See the [CLI
 - [x] Limit
 - [x] Aggregate
 - [x] UDFs
+  - [x] Scalar UDFs
+  - [x] Aggregate UDFs
 - [x] Common math functions
 - String functions
   - [x] Length of the string

rust/datafusion/src/datatyped.rs

@@ -0,0 +1,38 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! This module contains a public trait to annotate objects that know their data type.
+// The pattern in this module follows https://stackoverflow.com/a/28664881/931303
+
+use crate::error::Result;
+use arrow::datatypes::{DataType, Schema};
+
+/// Any object that knows how to infer its resulting data type from an underlying schema
+pub trait DataTyped: AsDataTyped {
+    fn get_type(&self, input_schema: &Schema) -> Result<DataType>;
+}
+
+/// Trait that allows DataTyped objects to be upcasted to DataTyped.
+pub trait AsDataTyped {
+    fn as_datatyped(&self) -> &dyn DataTyped;
+}
+
+impl<T: DataTyped> AsDataTyped for T {
+    fn as_datatyped(&self) -> &dyn DataTyped {
+        self
+    }
+}