module main

@[heap]
interface IGameObject {
mut:
    name       string
    parent     ?&IGameObject
    next       ?&IGameObject
    child      ?&IGameObject
    last_child ?&IGameObject
    add_child(mut o IGameObject)
}

@[heap]
struct GameObject implements IGameObject {
mut:
    name       string
    parent     ?&IGameObject
    next       ?&IGameObject
    child      ?&IGameObject
    last_child ?&IGameObject
}

fn (mut gameobject GameObject) add_child(mut o IGameObject) {
    o.parent = gameobject
    if gameobject.last_child != none {
        gameobject.last_child.next = o
    } else {
        gameobject.child = o
    }
    gameobject.last_child = o
}

fn test_main() {
    mut v1 := &GameObject{
        name: 'v1'
    }
    mut v2 := &GameObject{
        name: 'v2'
    }
    v1.add_child(mut v2)
    assert v1.child? == IGameObject(v2)
    assert v1.last_child? == IGameObject(v2)
}