Private classes in Ruby

gistfile1.rb

module Container
  class PublicThing
    def hello
      PrivateThing.new.hello
    end
  end

  class PrivateThing
    def hello
      "Hello, world!"
    end
  end
  private_constant :PrivateThing
end

Container::PublicThing.new.hello  # => "Hello, world!"
Container::PrivateThing.new.hello # => NameError!