new (Weak::Key)

    # File lib/Borges/Utilities/WeakIdentityKeyHash.rb, line 74
        def initialize(orig, hash)
          @internal_id = orig.object_id

          ObjectSpace.define_finalizer(orig, self.class.make_finalizer(@internal_id, hash.object_id))
          ObjectSpace.define_finalizer(self, self.class.make_finalizer(@internal_id, nil))

          Thread.exclusive do
            ID_MAP[@internal_id] = [] unless ID_MAP[@internal_id]
          end

          ID_MAP[@internal_id].push self.object_id
          ID_REV_MAP[self.object_id] = @internal_id
        end