#[derive(Debug)]
struct Item { sku: Vec<u8>, qty: i64, cents: i64 }
#[derive(Debug)]
struct Order { id: i64, customer: Vec<u8>, items: Vec<Item> }

fn main() {

fn parse_items(field: &[u8]) -> Vec<Item> {
    field.split(|&b| b == b';').map(|record| {
        let p: Vec<&[u8]> = record.split(|&b| b == b':').collect();
        let qty = std::str::from_utf8(p[1]).unwrap().parse::<i64>().unwrap();
        let cents = std::str::from_utf8(p[2]).unwrap().parse::<i64>().unwrap();
        Item { sku: p[0].to_vec(), qty, cents }
    }).collect()
}
let mut book: Vec<Order> = Vec::new();
book.push(Order { id: 1001, customer: b"alice".to_vec(),
                  items: parse_items(b"SKU-441:2:1999;SKU-7:1:500") });
for o in &book {
    let t: i64 = o.items.iter().map(|item| item.qty * item.cents).sum();
    use std::io::Write;
    let mut out=std::io::stdout().lock();
    out.write_all(&o.customer).unwrap();
    writeln!(&mut out," owes {t} cents over {} items",o.items.len()).unwrap();
}

assert_eq!(book[0].items[0].sku,b"SKU-441");assert_eq!(book[0].id,1001);
}