cheap callbacks using ruby modules

gistfile1.rb

module Rack
  module Cache
    class MetaStore
      module Base
        def lookup
          puts 'lookup'
        end
      end
      include Base
    end
  end
end

module MetaStoreFoo
  def lookup
    puts 'before lookup'
    super
    puts 'after lookup'
  end
end

store = Rack::Cache::MetaStore.new
store.lookup
Rack::Cache::MetaStore.send :include, MetaStoreFoo
store.lookup

# lookup
# before lookup
# lookup
# after lookup