From: David Alan Black <dblack@...>
Date: 2001-01-08T06:59:43+09:00
Subject: [ruby-talk:8788] Re: Backward Range implementation

Hello --

On Sun, 7 Jan 2001, Kevin Smith wrote:

> 
> Here's what I came up with that seems to work. I 
> didn't exhaustively test all the methods of 
> Range, but I think I probably hit the ones that 
> weren't working. Oh, I don't expect backward 
> ranges to support exclusive mode (it seems 
> unbalanced), so I didn't test that.
> 
> Gotta love this language!
> 
> Kevin
> 
> ==========================
> class Range
> 	alias old_each each
> 	def each(&block)
> 		if (first > last)
> 			first.downto(last) { |element| yield element}
> 			return self
> 		end
> 		return old_each(&block)
> 	end
> 	
> 	alias old_equal ===
> 	def ===(obj)
> 		if (first > last)
> 			return (last..first).old_equal(obj)
> 		end
> 		return old_equal(obj)
> 	end
> end

Using yours as a starting point, I tried to generalize it so that it
would work on strings as well as numbers.  I've resorted (so far) to
turning the range into an array.  (Which requires a bit of sleight of
hand, because Range#to_a seems to use Range#each, so one has to
sidestep the infinite recursion.)

I also factored it out a bit, just to reveal (to my own thick self)
exactly what was needed/involved.  And, like your version, this one
does not do anything about '...'.

Anyway.....

   class Range
     alias old_each each
     alias old_equal ===

     def downward
       first > last
     end

     def reverse
       last .. first
     end

     def ascending
       if downward
	 reverse
       else
	 self
       end
     end

     def each(&block)
       arr = []
       ascending.old_each do |e| arr.push e end
       arr.reverse! if downward
       arr.each &block
       return self
     end

     def ===(obj)
       ascending.old_equal(obj)
     end

     def show
       puts to_a.join ', '
     end

   end

   m = (5..0)
   n = ('d' .. 'a')

   m.show
   n.show

   __END__


Further thoughts/hacks/enhancements/whatever?


David

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