title: Does Objective-C support Mixin like Ruby?
body: <p>In Ruby, there's Modules and you can extend a class by "mixing-in" the module.</p>
  
  <pre><code>module MyModule
    def printone
      print "one" 
    end
  end
  
  class MyClass
    include MyModule
  end
  
  theOne = MyClass.new
  theOne.printone 
  &gt;&gt; one
  </code></pre>
  
  <p>In Objective-C, I find that I have a set of common methods that I want a number of Class to "inherit". What other ways can I achieve this without creating a common class and deriving all from that common class?</p>