snippet.rb

module Persistence
  def self.included(base)
    base.extend(ClassMethods)
  end

  def start_transaction
    puts "Starting transaction"
  end
  
  def commit
    puts "Comitting"
  end
  
  module ClassMethods
    def method_added(name)
      return if @__wrapping_transactional_method
      original_name = "#{name} without transaction"
      
      @__wrapping_transactional_method = true
      alias_method original_name, name
      define_method(name) do
        start_transaction
        send(original_name)
        commit
      end
      @__wrapping_transactional_method = false
    end
  end
end

class User
  include Persistence
  
  def save
    puts "Saving instance..."
  end
end

User.new.save