Interface WindowUDFImpl

datafusion/expr/src/udwf.rs:315–432

Trait for implementing [`WindowUDF`]. This trait exposes the full API for implementing user defined window functions and can be used to implement any function. While the trait depends on [`DynEq`] and [`DynHash`] traits, these should not be implemented directly. Instead, implement [`Eq`] and [`Hash`] and leverage the blanket implementations of [`DynEq`] and [`DynHash`]. See [`advanced_udwf.rs`]

///     .unwrap();
/// ```
pub trait WindowUDFImpl: Debug + DynEq + DynHash + Send + Sync + Any {
    /// Returns this function's name
    fn name(&self) -> &str;

    /// Returns any aliases (alternate names) for this function.
    ///
    /// Note: `aliases` should only include names other than [`Self::name`].
    /// Defaults to `[]` (no aliases)
    fn aliases(&self) -> &[String] {
        &[]
    }

    /// Returns the function's [`Signature`] for information about what input
    /// types are accepted and the function's Volatility.
    fn signature(&self) -> &Signature;

    /// Returns the expressions that are passed to the [`PartitionEvaluator`].
    fn expressions(&self, expr_args: ExpressionArgs) -> Vec<Arc<dyn PhysicalExpr>> {
        expr_args.input_exprs().into()
    }

    /// Invoke the function, returning the [`PartitionEvaluator`] instance
    fn partition_evaluator(
        &self,
        partition_evaluator_args: PartitionEvaluatorArgs,
    ) -> Result<Box<dyn PartitionEvaluator>>;

    /// Returns an optional hook for simplifying this user-defined window
    /// function.
    ///
    /// Use this hook to apply function-specific rewrites during optimization.
    /// The default implementation returns `None`.
    ///
    /// DataFusion already simplifies arguments and performs constant folding
    /// (for example, `my_add(1, 2) -> 3`), so there is usually no need to
    /// implement those optimizations manually for specific UDFs.
    ///
    /// Example:
    /// `advanced_udwf.rs`: <https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/udf/advanced_udwf.rs>
    ///
    /// # Returns
    /// `None` if simplify is not defined.
    ///
    /// Or, a closure ([`WindowFunctionSimplification`]) invoked with:
    /// * `window_function`: [WindowFunction] with already simplified
    ///   arguments
    /// * `info`: [crate::simplify::SimplifyContext]
    ///
    /// The closure returns a simplified [Expr] or an error.
    ///
    /// # Notes
    /// The returned expression must have the same schema as the original
    /// expression, including both the data type and nullability. For example,
    /// if the original expression is nullable, the returned expression must
    /// also be nullable, otherwise it may lead to schema verification errors
    /// later in query planning.
    fn simplify(&self) -> Option<WindowFunctionSimplification> {
        None