Macro create_udwf_expr

macro_rules! create_udwf_expr {
    ($UDWF:ident, $OUT_FN_NAME:ident, $DOC:expr) => { ... };
    ($UDWF:ident, $OUT_FN_NAME:ident, [$($PARAM:ident),+], $DOC:expr) => { ... };
}

Create a WindowFunction expression that exposes a fluent API which you can use to build more complex expressions.

Parameters

• $UDWF: The struct which defines the Signature of the user-defined window function.
• $OUT_FN_NAME: The basename to generate a unique function name like $OUT_FN_NAME_udwf.
• $DOC: Doc comments for UDWF.
• (optional) [$($PARAM:ident),+]: An array of 1 or more parameters for the generated function. The type of parameters is Expr. When omitted this creates a function with zero parameters.

Example

1. With Zero Parameters

use arrow::datatypes::FieldRef;

/// Creates `row_number()` API which has zero parameters:
///
///     ```
///     /// Returns a unique row number for each row in window partition
///     /// beginning at 1.
///     pub fn row_number() -> datafusion_expr::Expr {
///        row_number_udwf().call(vec![])
///     }
///     ```
create_udwf_expr!(
    RowNumber,
    row_number,
    "Returns a unique row number for each row in window partition beginning at 1."
);

2. With Multiple Parameters

use arrow::datatypes::FieldRef;
/// Creates `lead(expr, offset, default)` with 3 parameters:
///
///     ```
///     /// Returns a value evaluated at the row that is offset rows
///     /// after the current row within the partition.
///     pub fn lead(
///         expr: datafusion_expr::Expr,
///         offset: datafusion_expr::Expr,
///         default: datafusion_expr::Expr,
///     ) -> datafusion_expr::Expr {
///         lead_udwf().call(vec![expr, offset, default])
///     }
///     ```
create_udwf_expr!(
    Lead,
    lead,
    [expr, offset, default],
    "Returns a value evaluated at the row that is offset rows after the current row within the partition."
);