iis.rb

class IIS
  class Website
    def initialize(iis)
      @shell = iis.shell
    end
  end

  class Mailbox
  end

  module Chaining
    ATTRIBUTES = {website: :Website,
                  mailbox: :Mailbox}.freeze

    ATTRIBUTES.each do |name, const|
      define_method name do
        instance_variable_set "@#{name}", IIS.const_get(const).new(self)
      end
    end
  end

  include Chaining

  attr_reader :shell

  def initialize(shell:)
    @shell = shell
  end
end

IIS.new(shell: '🦪').website