> nil as a possible value for ref stays with us as it is required to unarm
> dangling pointers.
Can `nil` be somehow made illegal for owned refs only?
Since `immutable` would be annotated to the `ref` type, it seems misplaced
and/or like a misnomer to me: We don't want the `ref` to be immutable but the
object it refers to, and the immutability is conditional. How about one of
these:
type
Node {.protected.} = ref object # or maybe "restricted"
...
Node = ref protected object # breaks backwards compatibility and needs
parser extension
...
Run
