ludic/examples/events/scoped.ludic

# scoped.ludic — a despawned entity drops out of subsequent event-driven work
# (replaces tests/mod_c/scoped_mod.c, which tested entity-scoped foreign callbacks
# swept on despawn). Here a @On(Tick) listener counts live Units each tick; after
# the Unit is despawned, a further tick finds none. Fires twice before the kill,
# not the third time. Prints 2.
program Scoped {
  property Health { hp: int = 0 }
  model Unit { Health }
  state ScopedState {
    fires: int = 0
  }
  event Tick { }
  @On(Tick) handler OnTick(scoped_st: mut ScopedState) { for (Health) in query [Health, {Unit}] { scoped_st.fires += 1 } }

  entry (scoped_st: ScopedState) {
    spawn Unit { Health { hp: 1 } }
    emit Tick()     # 1 live Unit -> fires = 1
    emit Tick()     # fires = 2
    for (Health) in query [Health, {Unit}] { despawn self() }   # kill the Unit
    emit Tick()     # no live Units -> fires stays 2
    print(scoped_st.fires)    # 2
  }
}