logging_observer_proof_of_concept.rb

module LoggingObserver
  def self.included base
    base.extend ClassMethods
  end

  module ClassMethods
    def new *args
      @instance = super
      override_methods
      @instance
    end

    def override_methods
      @instance.class.instance_methods(false).each { |m| override_method m }
    end

    def override_method(m)
      @instance.instance_eval <<-code
        def #{m} *args
          klass  = self.class.name
          logger = eval "\#{klass}Logger.new"
          m      = __method__.to_s

          puts logger.instance_eval 'before_' + m.to_s if logger.respond_to? 'before_' + m.to_s
          super
          puts logger.instance_eval 'after_' + m.to_s if logger.respond_to? 'after_' + m.to_s
        end
      code
    end
  end
end

class RecordLogger
  def before_save
    'before the save'
  end

  def after_save
    'save done'
  end
end

class Record
  include LoggingObserver

  def save
    puts 'saving'
  end
end

Record.new.save
#=> before the save
#=> saving
#=> save done