From: Hal Fulton <hal9000@...>
Date: 2006-01-06T18:56:37+09:00
Subject: Re: Attribute writers

Michael Judge wrote:
> I'm working on a survey system in Ruby and am having a style crisis with 
> a simple bit of code that has left me paralyzed and unable to work.
> 
> Respondent data in research surveys is traditionally stored as big 
> strings of text like this: "123145992348241110111 11 11  1 1111 3331 1"
> 
> This was a made up example, in the real world however, there's sometimes 
> hundreds of thousands of characters in each respondent's data string. 
> In the stats and analysis section of my program, I'm working out how to 
> access subsets of these strings in an object-oriented way.
> 
> Something like this appeals to me and is very readable:
> 
> if currentRespondent.ascii(0..2) == 123
>   currentRespondent.ascii(0..2) = 777
> end
> 
> How would one actually implement this?

I'd suggest doing a little metaprogramming and making the final code
a little easier.

Here is a very rough outline -- if you like it I can help flesh out
the details:


class Respondent

   Fields = { :this => 0..2,
              :that => 3..6,
              :etc  => 7..10 }

   Fields.each_pair do |field,range|
     # add a reader basically doing @resp[range]
     # add a writer basically doing @resp[range]=val
   end

   def initialize(str)
     @resp = str
   end

end


resp = Respondent.new(whatever)
if resp.this == Something
   resp.this = SomethingElse
end
do_whatever if resp.that != resp.this


Make sense?

Hal