Function apply_replace

datafusion/functions/src/string/replace.rs:247–283

(
    builder: &mut B,
    string: &str,
    from: &str,
    to: &str,
)

#[inline]
fn apply_replace<B: BulkNullStringArrayBuilder>(
    builder: &mut B,
    string: &str,
    from: &str,
    to: &str,
) {
    // Hot path: single ASCII byte → single ASCII byte. An ASCII byte (< 0x80)
    // cannot appear inside a multi-byte UTF-8 sequence, so any multi-byte
    // sequences in `string` pass through unchanged and output stays valid
    // UTF-8.
    if let (&[from_byte], &[to_byte]) = (from.as_bytes(), to.as_bytes())
        && from_byte.is_ascii()
        && to_byte.is_ascii()
    {
        // SAFETY: see the contract above.
        unsafe {
            builder.append_byte_map(string.as_bytes(), |b| {
                if b == from_byte { to_byte } else { b }
            });
        }
        return;
    }

    if from.is_empty() {
        // Empty `from`: insert `to` before each character and at both ends.
        builder.append_with(|w| {
            w.write_str(to);
            for ch in string.chars() {
                w.write_char(ch);
                w.write_str(to);
            }
        });
        return;
    }

    builder.append_with(|w| replace_into_writer(w, string, from, to));
}

#[inline]
fn replace_into_writer<W: StringWriter>(w: &mut W, string: &str, from: &str, to: &str) {