-- Canary fixture (Task 2 review, Important 2): a real runtime trap,
-- proving the trap/ path end to end. `pair` takes two exclusive borrows
-- through runtime indices (docs/plan/oop-vm/08-builtin-surface.md's
-- residual-borrow case); calling it with i == j aliases the same
-- element under two exclusive borrows, which the VM's runtime guard
-- traps rather than silently corrupting.
class Item {
  n: Int
}

class Bag {
  items: multi Item
}

fn touch(mut a: Item, mut b: Item) -> Int {
  return a.n + b.n
}

fn pair(mut bag: Bag, i: Int, j: Int) -> Int {
  return touch(bag.items[i], bag.items[j])
}

fn main() {
  let bag = Bag { items: multi_new() }
  push(bag.items, Item { n: 1 })
  push(bag.items, Item { n: 2 })
  print_int(pair(bag, 0, 0))
}