fn main() {

struct Item { id: i32, weight: f32 }
let mut items: Vec<Item> = Vec::new();
items.push(Item { id: 1, weight: 0.5 });
let first = 0; // retain an index, not a reference across push
for i in 2..1_000_001 { items.push(Item { id: i, weight: 0.0 }); }
items[first].weight = 99.5;
println!("{} items, first is Item {{ {}, {} }}", items.len(), items[0].id, items[0].weight);

assert_eq!(items[first].weight,99.5);
}