Function generic_string_substr_copy

datafusion/functions/src/unicode/substr.rs:413–447

Fallback for `generic_string_substr` if we can't use zerocopy because the input string array is too large.

(
    string_array: &GenericStringArray<T>,
    args: &[ArrayRef],
)

// Fallback for `generic_string_substr` if we can't use zerocopy because the
// input string array is too large.
fn generic_string_substr_copy<T: OffsetSizeTrait>(
    string_array: &GenericStringArray<T>,
    args: &[ArrayRef],
) -> Result<ArrayRef> {
    let start_array = as_int64_array(&args[0])?;
    let count_array_opt = args.get(1).map(|a| as_int64_array(a)).transpose()?;

    let is_ascii = enable_ascii_fast_path(&string_array, start_array, count_array_opt);

    // Combine null bitmaps from all inputs in bulk.
    let nulls = NullBuffer::union_many([
        string_array.nulls(),
        start_array.nulls(),
        count_array_opt.and_then(|a| a.nulls()),
    ]);

    let len = string_array.len();
    let mut result_builder = StringViewArrayBuilder::with_capacity(len);

    for i in 0..len {
        if nulls.as_ref().is_some_and(|n| n.is_null(i)) {
            result_builder.append_placeholder();
            continue;
        }

        let string = string_array.value(i);
        let start = start_array.value(i);
        let count = count_array_opt.map(|a| a.value(i));

        let (byte_start, byte_end) = get_true_start_end(string, start, count, is_ascii)?;
        result_builder.append_value(&string[byte_start..byte_end]);
    }

    Ok(Arc::new(result_builder.finish(nulls)?) as ArrayRef)
}

#[cfg(test)]
mod tests {