From: donn@...
Date: 2007-02-11T08:55:07+09:00
Subject: Generating instance variable for a class

What I am trying to do is use a hash to tie attributes to an input
record layout from which the attribute will be created and their
values are set.  What I am thinking is that the hash can provide the
record layout to class users and it can provide loop control for
nearly everything associated with it.  I would like to create an
attribute for each hash key.  It would be great if I could use "attr"
to create the instance and and associated access method.  The
following does function, but it looks like a kludge.  Is there a
better way of doing it?

class MDhdr < MD_Record		# Header record
   attr_reader :infmt
   def initialize(rec)
      @infmt = {
          :JobId => [0,7],
          :Version => [8,11],
          :HistorySeq => [12,15],
          :HistorStatus => [16,16],
          :HistoryId => [17,24],
          :UserJobId => [25,49],
          :JobName => [50,79]
      }.each {|key,arg| eval "@#{key} = rec[#{arg[0]}..#{arg[1]}]" }
      puts @JobId

   end
end

The ultimate goals here are lazy, accuracy, and no reduncancy.  I can
update the hash with new record layout positions and a instance name,
and I'm done with updating the class.  The alternative is to have an
attr_accessor for all the variables, a listing of all the variables,
and each variable assigned.

Thanks for your recommendations.