From: Robert Klemme <bob.news@...>
Date: 2006-01-06T19:32:59+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?
>
> 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!

Hm, I wouldn't use a string internally at all - at least not if you are
trying to do it OO.  This is what I'd do:

class Results
  include Enumerable

  def initialize(from_string = "")
    @fields = from_string.split(/\s+/).map {|s| s.to_i}
  end

  def field() @fields end

  def each(&b)
    @fields.each(&b)
    self
  end

  def size() @fields.size end
  def empty?() @fields.empty? end

  def to_str
    @fields.map {|d| d.to_s}.join ' '
  end

  alias :to_s :to_str

  def to_a() @fields end
end

You could also simply subclass Array and create appropriate constructors
and to_s, to_str methods:

class Results < Array
  def initialize(from_string = "")
    super( from_string.split(/\s+/).map! {|s| s.to_i} )
  end

  def to_str
    map {|d| d.to_s}.join ' '
  end

  alias :to_s :to_str
end

HTH

Kind regards

    robert