Iterate over collections and text

for visits list elements, dictionary keys, set elements, range integers, or characters of a string. A character is a one-character str.

def main() -> Result[(), AllocError | IoError | OverflowError[i64]]:
    mut total = 0
    for n in range(1, 5):
        total = total + n
    print(total)?

    scores = {"Ada": 10, "Grace": 20}?
    for name in &scores:
        print(name)?
        print(scores[name])?

    print(list(range(5, 0, -2))?)?
    for character in "hé":
        print(character)?
    Ok(())

10
Ada
10
Grace
20
[5, 3, 1]
h
é

range(stop) starts at zero; the stop is excluded. A step may be negative but never zero: it is a NonZero[i64]. Ranges can be reused and do not allocate; list(range(5))? allocates the list. String iteration yields characters without allocating.

Ranges default to i64. Use range[u8](8) or a typed bound to choose another element type. Start and stop must fit it; the step remains a signed NonZero[i64].

The iterable is evaluated once. Iterating an owned collection transfers it into the loop; use for item in &values to preserve the owner. Borrowed iteration prevents conflicting mutation; owned list elements become shared references. Use &mut values for mutable element references. To iterate a snapshot while mutating the original, use for item in copy(values)?.