fn starts_with()

in crates/iceberg/src/expr/visitors/page_index_evaluator.rs [583:647]
52 lines of code
6 McCabe index (conditional complexity)

    fn starts_with(
        &mut self,
        reference: &BoundReference,
        datum: &Datum,
        _predicate: &BoundPredicate,
    ) -> Result<RowSelection> {
        let field_id = reference.field().id;

        let PrimitiveLiteral::String(datum) = datum.literal() else {
            return Err(Error::new(
                ErrorKind::Unexpected,
                "Cannot use StartsWith operator on non-string values",
            ));
        };

        self.calc_row_selection(
            field_id,
            |min, max, nulls| {
                if matches!(nulls, PageNullCount::AllNull) {
                    return Ok(false);
                }

                if let Some(lower_bound) = min {
                    let PrimitiveLiteral::String(lower_bound) = lower_bound.literal() else {
                        return Err(Error::new(
                            ErrorKind::Unexpected,
                            "Cannot use StartsWith operator on non-string lower_bound value",
                        ));
                    };

                    let prefix_length = lower_bound.chars().count().min(datum.chars().count());

                    // truncate lower bound so that its length
                    // is not greater than the length of prefix
                    let truncated_lower_bound =
                        lower_bound.chars().take(prefix_length).collect::<String>();
                    if datum < &truncated_lower_bound {
                        return Ok(false);
                    }
                }

                if let Some(upper_bound) = max {
                    let PrimitiveLiteral::String(upper_bound) = upper_bound.literal() else {
                        return Err(Error::new(
                            ErrorKind::Unexpected,
                            "Cannot use StartsWith operator on non-string upper_bound value",
                        ));
                    };

                    let prefix_length = upper_bound.chars().count().min(datum.chars().count());

                    // truncate upper bound so that its length
                    // is not greater than the length of prefix
                    let truncated_upper_bound =
                        upper_bound.chars().take(prefix_length).collect::<String>();
                    if datum > &truncated_upper_bound {
                        return Ok(false);
                    }
                }

                Ok(true)
            },
            MissingColBehavior::CantMatch,
        )
    }