From: David Alan Black <dblack@...>
Date: 2001-08-16T07:53:16+09:00
Subject: [ruby-talk:19851] Re: Why not?: Assigning to self

Hello --

On Thu, 16 Aug 2001, Jean Michel wrote:

> I came upon  something which is perhaps an exemple  where one might want
> to change self, or perhaps just I  did not find the right way to achieve
> my aim.
>
> I came upon a situation which could be handled nicely by adding a couple
> of  methods to  the class  Range (I  will elaborate  the situation  in a
> further message if people are interested):

I'd be interested.  I don't know why Ranges are immutable, but
assuming that we get a convincing explanation, I'd like to see what
the best solution to your problem will then be :-)

>
> Class Range
>   def shrink_up
>     @begin+=1
>   end
>   def shrink_down
>     @end-=1
>   end
> end
>
> Well,  this  does  not  work  since  begin  and  end  are  not  writable
> attributes (nor attributes at all, in fact). The next try would be :)
>
> Class Range
>   def shrink_up
>     self=(begin+1..end)
>   end
>   def shrink_down
>     self=(begin..end-1)
>   end
> end


I don't know if this helps in your situation, but you could do a sort
of faux version of it:

  class Range
    def shrunk_up(n=1)
      (first + n .. last)
    end
    def shrunk_down(n=1)
      (first .. last - n)
    end
  end

  r = (0..10)
  p r.shrunk_up(3)   # => 3..10
  p r.shrunk_down    # => 0..9


It's a typing-saver, at best, but maybe useful.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav