From: Rick DeNatale <rick.denatale@...>
Date: 2007-06-06T06:02:08+09:00
Subject: Re: Reverse-range alternatives?

First let me take the liberty of reversing the top posting:
On 6/5/07, Kenneth McDonald <kenneth.m.mcdonald@sbcglobal.net> wrote:
> Daniel DeLorme wrote:
> >
> > I can't resist this one...
> >
> > class Range
> >   def reverse
> >     r = dup
> >     def r.each(&block)
> >       last.downto(first, &block)
> >     end
> >     r
> >   end
> > end
>
> I'd thought of that, but it's simply too risky. Changing the behavior of
> something as fundamental as Range could really screw up if another
> required module counted on that behavior.
>
> Generally, I'll reopen a class to add methods to it, but not to change
> its behavior.

Actually if you look carefully that's what his code does.  He added a
method to range which returns a new instance of range with a singleton
method which overrides each.  Normal instances of range won't be
affected.

It's a nice usage of the nested method definitions we were discussing recently.

Bravo Daniel.

Of course the reversed range should probably also invariants like:

    (1..3).reverse.last == (1..3).reverse.to_a.last

And methods like to_s and step should also do the right thing too.

If you want to go that far it's probably better to have a ReverseRange
class and have the Range#reverse return an instance of that.

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/