n.builtins.Ref_as_key: wrapper to store references in collections
n.builtins.Ref_as_key: wrapper to store references in collections

References are not `Has_equality (they have === but not ==) so cannot be
used as keys in collections directly. This wrapper struct gives
references a `Map_key intf.

nanocritical/n,nanocritical/n,nanocritical/n,nanocritical/n