def each_key(&block)
      raise NotImplementedError, "each_key is not supported on this proxy" \
        unless supports? :each_key

      return enum_for(:each_key) unless block_given?
      adapter.each_key(&block)
      self
    end
def each_key(&block)
      raise NotImplementedError, "each_key is not supported on this proxy" \
        unless supports? :each_key

      return enum_for(:each_key) unless block_given?
      adapter.each_key(&block)
      self
    end
(see Defaults#each_key)