#[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() {
let book=vec![Order {id:1,customer:vec![],items:vec![]}];
for o in &book { println!("{o:?}"); }
println!("{:?}", book[0]); // valid: Vec<Order> has fixed-size, indexable elements
assert_eq!(book[0].id,1);
}