From: dblack@...
Date: 2002-09-30T09:25:14+09:00
Subject: Re: thoughts on typelessness

Hi --

On Mon, 30 Sep 2002, Pit Capitain wrote:

> On 29 Sep 2002, at 12:09, dblack@candle.superlink.net wrote:
>
> >    def sort_key
> >      @sort_key - 1
> >    rescue NameError
> >      @sort_key
> >    end
>
> When you announced dbdbd I quickly browsed through the code. I
> had the impression that I understood your well written program -
> besides this very example. I really tried to understand what's going
> on, but I just couldn't get it.

Whoops :-)

>   def sort_key
>     if @sort_key.is_a? Integer
>       @sort_key - 1
>     else
>       @sort_key
>     end
>   end
>
> I'm sure it would be very interesting to try to program without #type,
> #is_a? etc and I'm sure I will try to do so in the future, but for me
> this wasn't a good example. If you think so, too, maybe you could
> find an other implementation. I'd be very interested in what you'd
> come up with.

One direction one can go in -- probably heavy overkill for this
example, but anyway -- is extending the capacity of objects.

  module MinusStub
    def -(val)
      self
    end
  end

  class Thing
    def sort_key
      @sort_key - 1
    end

    def sort_key=(val)
      @sort_key = val
      @sort_key.extend(MinusStub) unless @sort_key.respond_to?(:-)
    end
  end

  if __FILE__ == $0
    t = Thing.new
    t.sort_key = 5
    p t.sort_key          # 4
    p t.sort_key * 10     # 40
    t.sort_key = "Hello"
    p t.sort_key          # "Hello"
  end

(I know there are some issues about this approach to maintaining a
simultaneously 0- and 1-originating array... but I won't go into all
of that here :-)

I actually really like Massimiliano's #can? idea:

  @sort_key.extend(MinusStub) unless @sort_key.can?(:-)

looks nice to me, and slightly more abstracted (in a good way, I
think) than respond_to?


David

-- 
David Alan Black                      | Register for RubyConf 2002!
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