Private module methods in Ruby

I have a two part question

Best-Practice

I have an algorithm that performs some operation on a data structure using the public interface
It is currently a module with numerous static methods, all private except for the one public interface method.
There is one instance variable that needs to be shared among all the methods.

These are the options I can see, which is the best?:

Module with static ('module' in ruby) methods
Class with static methods
Mixin module for inclusion into the data structure
Refactor out the part of the algorithm that modifies that data structure (very small) and make that a mixin that calls the static methods of the algorithm module

Technical part

Is there any way to make a private Module method?

module Thing
  def self.pub; puts "Public method"; end
  private
  def self.priv; puts "Private method"; end
end

The private in there doesn't seem to have any effect, I can still call Thing.priv without issue.

Solution

I think the best way (and mostly how existing libs are written) to do this is by creating a class within the module that deals with all the logic, and the module just provides a convenient method, e.g.

module GTranslate
  class Translator
    def perform(text)
      translate(text)
    end

    private

    def translate(text)
      # do some private stuff here
    end
  end

  def self.translate(text)
    t = Translator.new
    t.perform(text)
  end
end