Mildly insane examples of overriding the reader method of the ActiveSupport provided :class_attribute directly and as part of an ActiveSupport::Concern.

the_cats_meow.rb

class Feline
  class_attribute :meow

  self.meow = '<feline-silence/>'
  def self.meow
    raise NotImplementedError
  end
end

class MetaCat < Feline
end

metacat = MetaCat.new

class Cat < Feline
  self.meow = 'meow!'
end

class Lion < Cat
  self.meow = 'roar!'
end
simba = Lion.new
simba.meow = 'Hakuna Matata'


module FelineMutagen
  extend ActiveSupport::Concern

  included do
    class_attribute :meow
    self.meow = 'The inner thoughts of cats'

    def self.meow
      '^^30\/\/'
    end
  end

  module ClassMethods
    def meow
      # Class methods are added before included block is executed so...
      raise ErrorThatDoesNotExistBecauseThisCodeWillNotBeCalled
    end
  end
end

class ComicbookFeline
  include FelineMutagen
end

class Catwoman < ComicbookFeline
  self.meow = 'DC Comics is better than Marvel.'
end

anne_hathaway = Catwoman.new
anne_hathaway.meow = 'Seriously.'

[Feline, MetaCat, metacat].each_with_index do |kitty, index|
  case index
  when 0
    print "Felines are an abstract class, so their meow says \""
  when 1
    print "The same goes for MetaCat: \""
  when 2
    print "And an instance of MetaCat: \""
  end
  begin
    kitty.meow
  rescue NotImplementedError => e
    puts "#{e.message}\""
  end
end

puts "but the Cat class says \"#{Cat.meow}\""
puts "so Cat instances say \"#{Cat.new.meow}\""
puts "a Lion is kind of like a Cat, but it says \"#{Lion.meow}\""
puts "Except for Simba, he says \"#{simba.meow}\""

puts "\nBut sometimes in the comic books some kind of mutagen agent makes a feline of a non-feline. What then?"
puts "Feline mutants as a class might say \"#{ComicbookFeline.meow}\""
puts "So an instance of a generic feline mutant would say \"#{ComicbookFeline.new.meow}\""

puts "But Catwoman is not generic, so her class says \"#{Catwoman.meow}\""
puts "And a Catwoman instance (I'm thinking Anne Hathaway) says \"#{anne_hathaway.meow}\""

puts "\nBut the inner thoughts of Comicbook Felines? We may never know."

# =>
# Felines are an abstract class, so their meow says "NotImplementedError"
# The same goes for MetaCat: "NotImplementedError"
# And an instance of MetaCat: "NotImplementedError"
# but the Cat class says "meow!"
# so Cat instances say "meow!"
# a Lion is kind of like a Cat, but it says "roar!"
# Except for Simba, he says "Hakuna Matata"
#
# But sometimes in the comic books some kind of mutagen agent makes a feline of a non-feline. What then?
# Feline mutants as a class might say "^^30\/\/"
# So an instance of a generic feline mutant would say "^^30\/\/"
# But Catwoman is not generic, so her class says "DC Comics is better than Marvel."
# And a Catwoman instance (I'm thinking Anne Hathaway) says "Seriously."
#
# But the inner thoughts of Comicbook Felines? We may never know.