Function str_to_map_impl

datafusion/spark/src/function/map/str_to_map.rs:180–260

(
    text_array: V,
    pair_delim_array: Option<V>,
    kv_delim_array: Option<V>,
)

}

fn str_to_map_impl<'a, V: StringArrayType<'a> + Copy>(
    text_array: V,
    pair_delim_array: Option<V>,
    kv_delim_array: Option<V>,
) -> Result<ArrayRef> {
    let num_rows = text_array.len();

    // Precompute combined null buffer from all input arrays.
    // NullBuffer::union_many performs a bitmap-level AND, which is more
    // efficient than checking per-row nullability inline.
    let combined_nulls = NullBuffer::union_many([
        text_array.nulls(),
        pair_delim_array.as_ref().and_then(|a| a.nulls()),
        kv_delim_array.as_ref().and_then(|a| a.nulls()),
    ]);

    // Use field names matching map_type_from_key_value_types: "key" and "value"
    let field_names = MapFieldNames {
        entry: "entries".to_string(),
        key: "key".to_string(),
        value: "value".to_string(),
    };
    let mut map_builder = MapBuilder::new(
        Some(field_names),
        StringBuilder::new(),
        StringBuilder::new(),
    );

    let mut seen_keys = HashSet::new();
    for row_idx in 0..num_rows {
        if combined_nulls.as_ref().is_some_and(|n| n.is_null(row_idx)) {
            map_builder.append(false)?;
            continue;
        }

        // Per-row delimiter extraction
        let pair_delim =
            pair_delim_array.map_or(DEFAULT_PAIR_DELIM, |a| a.value(row_idx));
        let kv_delim = kv_delim_array.map_or(DEFAULT_KV_DELIM, |a| a.value(row_idx));

        let text = text_array.value(row_idx);
        if text.is_empty() {
            // Empty string -> map with empty key and NULL value (Spark behavior)
            map_builder.keys().append_value("");
            map_builder.values().append_null();
            map_builder.append(true)?;
            continue;
        }

        seen_keys.clear();
        for pair in text.split(pair_delim) {
            if pair.is_empty() {
                continue;
            }

            let mut kv_iter = pair.splitn(2, kv_delim);
            let key = kv_iter.next().unwrap_or("");
            let value = kv_iter.next();