smart_flash.rb

#!/usr/bin/ruby

class Flash < Hash
  class List < Array
    def to_s
      map {|v| "<li>#{v}</li>" }.join('')
    end 
  end 
  def []= k, v
    super(k, List.new(fetch(k, []) + [v]))
  end 
end


flash = Flash.new {|h,k| h[k] = Flash::List.new }

flash[:success] = "This worked"
flash[:success] = "This worked too!"

puts flash[:success]
puts flash[:success].to_s