# An in-memory model: reserve workspace slots, then release them.
struct workspace:
    available: i32

struct reservation:
    owner: workspace
    slots: i32

func (booking reservation) deinit():
    booking.owner.available += booking.slots

func reserve(space: workspace, slots: i32) -> reservation:
    space.available -= slots
    return reservation(owner = space, slots = slots)

func entry(capacity: i32) -> i32:
    var space = workspace(available = capacity)
    with reserve(space, 2) as booking:
        # The two reserved slots belong to this scope.
        pass
    return space.available