Storing a reference to a stage in a layer is problematic, because it is not kept in sync: the user must still add the layer into the stage, and there is no way to update the reference if the layer is removed from the stage or added into a different stage. Therefore, calling Layer#stage() offers no guarantee that the return value is correct. Since a layer is an otherwise immutable data structure, it seems sensible to remove the stage reference entirely. Unfortunately, this is a breaking change for clients that instantiate Layer directly.
Latest commit 7c55c85
Oct 29, 2018