Jefffrey commented on code in PR #15911:
URL: https://github.com/apache/datafusion/pull/15911#discussion_r2476288257
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datafusion/expr/src/udaf.rs:
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@@ -674,6 +681,31 @@ pub trait AggregateUDFImpl: Debug + Send + Sync {
/// the arguments
fn return_type(&self, arg_types: &[DataType]) -> Result<DataType>;
+ /// What type will be returned by this function, given the arguments?
+ ///
+ /// By default, this function calls [`Self::return_type`] with the
+ /// types of each argument.
+ ///
+ /// # Notes
+ ///
+ /// Most UDFs should implement [`Self::return_type`] and not this
+ /// function as the output type for most functions only depends on the
types
+ /// of their inputs (e.g. `sum(f64)` is always `f64`).
+ ///
+ /// This function can be used for more advanced cases such as:
+ ///
+ /// 1. specifying nullability
+ /// 2. return types based on the **values** of the arguments (rather than
+ /// their **types**.
Review Comment:
Thanks for checking, I'll clean this up in a PR later 👍
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