Function case_conversion_array

datafusion/functions/src/string/common.rs:410–449

(
    array: &ArrayRef,
    lower: bool,
)

}

fn case_conversion_array<O: OffsetSizeTrait>(
    array: &ArrayRef,
    lower: bool,
) -> Result<ArrayRef> {
    const PRE_ALLOC_BYTES: usize = 8;

    let string_array = as_generic_string_array::<O>(array)?;
    if string_array.is_ascii() {
        return case_conversion_ascii_array::<O>(string_array, lower);
    }

    // Values contain non-ASCII.
    let item_len = string_array.len();
    let offsets = string_array.value_offsets();
    let start = offsets.first().unwrap().as_usize();
    let end = offsets.last().unwrap().as_usize();
    let capacity = (end - start) + PRE_ALLOC_BYTES;
    // Null-preserving: reuse the input null buffer as the output null buffer.
    let nulls = string_array.nulls().cloned();
    let mut builder = GenericStringArrayBuilder::<O>::with_capacity(item_len, capacity);

    if let Some(ref n) = nulls {
        for i in 0..item_len {
            if n.is_null(i) {
                builder.append_placeholder();
            } else {
                // SAFETY: `n.is_null(i)` was false in the branch above.
                let s = unsafe { string_array.value_unchecked(i) };
                builder.append_value(&unicode_case(s, lower));
            }
        }
    } else {
        for i in 0..item_len {
            // SAFETY: no null buffer means every index is valid.
            let s = unsafe { string_array.value_unchecked(i) };
            builder.append_value(&unicode_case(s, lower));
        }
    }
    Ok(Arc::new(builder.finish(nulls)?))
}

/// Fast path for case conversion on an all-ASCII `StringViewArray`.
fn case_conversion_utf8view_ascii(