gistfile1.rb

require 'test/unit'

class SubsectionGraph
  # This gives us access to the class's singleton object which will sit between the actual Class structure and 
  # any instances and child classes
  #
  # If you're using metaid, this can be replaced by something like:
  # meta_eval do
  #   def prefix(p = nil)
  #     ...
  #   end
  # end
  class << self
    def prefix(p = nil)
      # Being used as a reader to return the existing one
      return @prefix unless p
      
      # Use an instance variable, but it's an instance variable of a Class object
      @prefix = p
    end
  end
  
  def initialize(num)
    @num = num
  end
  
  def full_name
    # It sees prefix (as defined above) as a class method, even though it's on the singleton/meta class.
    "#{self.class.prefix}-#{@num.to_s}"
  end
end

class FooGraph < SubsectionGraph
  prefix "foo"
end

class BarGraph < SubsectionGraph
  prefix "bar"
end

# A little test to make sure this actually works
class MetaTest < Test::Unit::TestCase
  def setup
    @foo = FooGraph.new(25)
    @bar = BarGraph.new(30)
  end
  
  def test_full_names
    assert_equal("foo-25", @foo.full_name)
    assert_equal("bar-30", @bar.full_name)
  end
end