From: Ross Bamford <rosco@...>
Date: 2006-01-06T19:03:14+09:00
Subject: Re: Attribute writers

On Fri, 06 Jan 2006 09:16:50 -0000, Michael Judge  
<mjudge@surveycomplete.com> 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?
>

Is this any help?

	irb(main):006:0> s = "123145992348241110111 11 11  1 1111 3331 1"
	  => "123145992348241110111 11 11  1 1111 3331 1"
	irb(main):007:0> s[0..2]
	  => "123"
	irb(main):008:0> s[0..2] = '777'
	  => "777"
	irb(main):009:0> s
	  => "777145992348241110111 11 11  1 1111 3331 1"

> class Respondent
>   def ascii(range)
>     return @ascii[range]
>   end
>
>   # doesn't work
>   def ascii(range)=(value)
>     @ascii[range] = value
>   end
> end
>
> currentRespondent = Respondent.new
>
> This is broken code, as Ruby doesn't like me trying to do "def
> a(b)=(c)".  There's other ways to accomplish the same purpose (e.g. def
> setter(range,value)) but I'm obsessed with the attribute writer form --
> which is just so dang cool.
>
> Anyone have some light they could spare?
>
> Argh.  I've been struggling with this for a week!
>

As far as I'm aware you can't do indexed attribute writers. You can of  
course do:

	def []=(idx, val)
	  puts "at #{idx} = #{val}"
	end

But Ruby won't have it if you prefix the [] with a name.

What I think I'd do is just remove the writer (for this purpose) and have  
ascii return a String. The you can do:

	if currentRespondent[0..2] == '777'
	  currentRespondent.ascii[0..2] = "123"
	end

(since String's [] is pretty flexible as I showed above)

But I have a feeling I may have missed something in your question. Is that  
helpful?

-- 
Ross Bamford - rosco@roscopeco.remove.co.uk