title: Accessing included class's protected constant in a ActiveSupport::Concern
body: <p>What's the simplest way to access included class's protected constant in the ActiveSupport::Concern context?</p>
  
  <p>Example classes:</p>
  
  <pre><code>module Printable
      extend ActiveSupport::Concern
  
  private
      def print_constant
          puts MY_CONSTANT
      end
  end
  
  class Printer
      include Printable
  
      def print
          print_constant
      end
  
  private
      MY_CONSTANT = 'Hello'.freeze
  end
  </code></pre>
  
  <p>This solution produces an error:</p>
  
  <pre><code>NameError: uninitialized constant Printable::MY_CONSTANT
  </code></pre>
  
  <p>I'm aware of an alternative that seems to work:</p>
  
  <pre><code>puts self.class::MY_CONSTANT
  </code></pre>
  
  <p>But, it doesn't feel right. :-)</p>
  
  <p>Any better suggestions?</p>