If the only thing you care about is behavior then ruby suggests to implement it as a module

(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at: lawrence@krubner.com

Interesting: 

Lets look at this ruby code.

class Util
  def self.double(i)
   i*2
  end
end

Util.double(4) #=> 8

Here we have a Util class. But notice that all the methods on this class are class methods. This class does not have any instance variables. Usually a class is used to carry both data and behavior and ,in this case, the Util class has only behavior and no data.
Similar utility tools in ruby

Now to get some perspective on this discussion lets look at some ruby methods that do similar thing. Here are a few.

require 'base64'
Base64.encode64('hello world') #=> "aGVsbG8gd29ybGQ=\n"

require 'benchmark'
Benchmark.measure { 10*2000 }

require 'fileutils'
FileUtils.chmod 0644, 'test.rb'

Math.sqrt(4) #=> 2

In all the above casese the class method is invoked without creating an instance first. So this is similar to the way I used Util.double .

However lets see what is the class of all these objects.

Base64.class #=> Module
Benchmark.class #=> Module
FileUtils.class #=> Module
Math.class #=> Module

So these are not classes but modules. That begs the question why the smart guys at ruby-core implemented them as modules instead of creating a class the way I did for Util.

Reason is that Class is too heavy for creating only methods like double. As we discussed earlier a class is suppossed to have both data and behavior. If the only thing you care about is behavior then ruby suggests to implement it as a module.
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