Borrow records in a collection

For a list of records, &items yields shared references and &mut items yields mutable references. The list cannot grow, shrink, or move during either loop:

class Score:
    value: i64

def main() -> Result[(), AllocError | IoError | OverflowError[i64]]:
    mut scores = [Score(2), Score(5)]?
    for score in &mut scores:
        score.value = score.value + 1
    print([score.value for score in &scores]?)?
    mut numbers = [10, 20]?
    for number in &mut numbers:
        *number = *number + 2
    print(numbers)?
    Ok(())

[3, 6]
[12, 22]

For large primitive-field records scanned a few fields at a time, consider columnar storage. Ordinary lists retain the full record-borrowing interface used here.