pub type EventListener[T] = fn (T) !

pub struct EventController[T] {
mut:
    id        int
    listeners map[int]EventListener[T]
}

fn (mut ec EventController[T]) generate_id() int {
    return ec.id++
}

pub fn (mut ec EventController[T]) override(listener EventListener[T]) EventController[T] {
    ec.listeners.clear()
    return ec.listen(listener)
}

pub fn (mut ec EventController[T]) listen(listener EventListener[T]) EventController[T] {
    ec.listeners[ec.generate_id()] = listener
    return ec
}

struct Foo {}

struct Bar {}

fn make[T](i int) EventController[T] {
    return EventController[T]{
        id: i
    }
}

fn test_main() {
    mut a := EventController[Foo]{
        id:        1
        listeners: {
            1: fn (a Foo) ! {
                dump(1)
            }
        }
    }
    assert dump(a).id == 1
    assert dump(a).listeners.len == 1
    a.override(fn (a Foo) ! {
        dump(2)
    })
    assert dump(a).id == 2
    assert dump(a).listeners.len == 1
}