Function split_helper 

pub fn split_helper<'a, F, I>(
    ca: &'a ChunkedArray<StringType>,
    by: &'a ChunkedArray<StringType>,
    op: F,
) -> Result<ChunkedArray<ListType>, PolarsError>
where
    F: Fn(&'a str, &'a str) -> I,
    I: Iterator<Item = &'a str>,

Available on crate feature polars-ops only.