hook_method.rb

require 'debugger'

class Node
  def to_s
    "new hotness"
  end
end

class Module
  def method_added(method_id)
    puts "added method #{ method_id } to #{ self } (which is a #{ self.class })."

    if self.ancestors.include?(Node) && method_id == :to_s && ! self.respond_to?(:hooked?)
      puts "  ==> redefining..."

      self.class_eval do
        alias_method :original_to_s, :to_s

        def self.hooked?
          true
        end

        def to_s(*args)
          super(*args) + ' ' + original_to_s
        end
      end
    end
  end
end

class SubNode < Node
  def to_s
    "old & busted"
  end
end


puts Node.new
puts SubNode.new