common_macro

Attribute Macro range_fn

source 
#[range_fn]
Expand description

Attribute macro to convert an arithimetic function to a range function. The annotated function should accept servaral arrays as input and return a single value as output.

This procedure macro can works on any number of input parameters. Return type can be either primitive type or wrapped in Option.

§Example

Take count_over_time() in PromQL as an example:

ⓘ
/// The count of all values in the specified interval.
#[range_fn(
    name = "CountOverTime",
    ret = "Float64Array",
    display_name = "prom_count_over_time"
)]
pub fn count_over_time(_: &TimestampMillisecondArray, values: &Float64Array) -> f64 {
     values.len() as f64
}

§Arguments

  • name: The name of the generated ScalarUDF struct.
  • ret: The return type of the generated UDF function.
  • display_name: The display name of the generated UDF function.