fn starts_with()

in crates/iceberg/src/expr/visitors/inclusive_metrics_evaluator.rs [296:352]
44 lines of code
6 McCabe index (conditional complexity)

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

        if self.contains_nulls_only(field_id) {
            return ROWS_CANNOT_MATCH;
        }

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

        if let Some(lower_bound) = self.lower_bound(field_id) {
            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 ROWS_CANNOT_MATCH;
            }
        }

        if let Some(upper_bound) = self.upper_bound(field_id) {
            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 ROWS_CANNOT_MATCH;
            }
        }

        ROWS_MIGHT_MATCH
    }