compat_test.nim

type
  GenericSceneObj* = ref object

  SceneNode* = ref object
    children*: seq[SceneNode]
    parent*: SceneNode

    sceneObj*: GenericSceneObj

  GameObj* = ref object
    name: string

  AnotherGameObj* = ref object
    health: int

# I want to make GameObj and AnotherGameObj to be compatible with GenericSceneObj,
# so I can store them in SceneNode
# Is it possible without inheriting from GenericSceneObj?

# I've tried using user defined type classes,
# but couldn't get them to work (probably using them in a wrong way)

udtc_test.nim

type

  GenericSceneObj* = concept x
    draw(x)

  SceneNode* = ref object
    children*: seq[SceneNode]
    parent*: SceneNode

    sceneObj*: GenericSceneObj

proc newSceneNode* (sceneObj: GenericSceneObj): SceneNode =
    result = SceneNode(sceneObj: sceneObj)
    newSeq(result.children, 10)

proc attachChild* (this: SceneNode, child: SceneNode) =
  child.parent = this
  this.children.add(child)

# udtc_test.nim(16, 18) Error: invalid type: 'GenericSceneObj' in this context: 'proc (SceneNode, SceneNode)'