instrument_FG_for_single_point_of_object_creation( used for logging in this case).rb

class << Factory
  alias_method :__build__, :build
  def build *args, &blk
    __log__( *args )
    __build__( *args, &blk )
  end

  private
  def __log__ *args
    @__logfile__ ||= File::new( "xxx", "w" )
    @__logfile__.puts( caller[2].to_s + args.inspect )
  end
end