From: Shin Nishiyama <shin@...>
Date: 2003-09-05T13:27:56+09:00
Subject: Re: Difference between .. and ... in boolean ranges

Hi!

I think i can answer. 

When operator '..' or '...' is used in the condition expression,
it works like a flip-flop switch and returns true/false
(default is false).
The difference of the two is the timing of evaluation.
I think it is Perl-like.

a=[1,2,'a',3,4,5,6,'b',7,8,9]

a.each do |x|
 if (x == 'a')..(x.is_a? String)
   print x
 end
end
#=> a

a.each do |x|
 if (x == 'a')...(x.is_a? String)
   print x
 end
end
#=> a3456b


Oliver Dain <odain2@nospam.mindspring.com> wrote

>I'm a bit confused by some Ruby behavior I'm seeing with ranges.  As I 
>understand it the difference between
>
>0..5
>
>and 
>
>0...5
>
>is that the former includes the number 5 while the 2nd does not.  That 
>seems to be the case, but one would expect the same type of behavior 
>in boolean context.  For example, I'd think
>
>0.upto(9) do |x|
>  if (x==3)..(x==5)
>    puts "In the range: #{x}"
>  else
>    puts "Not in the range: #{x}"
>  end
>end
>
>Would output:
>
>Not in the range: 0
>Not in the range: 1
>Not in the range: 2
>In the range: 3
>In the range: 4
>In the range: 5
>Not in the range: 6
>Not in the range: 7
>Not in the range: 8
>Not in the range: 9
>
>while using the 3 dot form like this:
>
>0.upto(9) do |x|
>  if (x==3)...(x==5)
>    puts "In the range: #{x}"
>  else
>    puts "Not in the range: #{x}"
>  end
>end
>
>Would output:
>
>Not in the range: 0
>Not in the range: 1
>Not in the range: 2
>In the range: 3
>In the range: 4
>Not in the range: 5
>Not in the range: 6
>Not in the range: 7
>Not in the range: 8
>Not in the range: 9
>
>However, the 3 dot form doesn't work as expected.  It outputs the same 
>as the 2 dot form (which works as expected).  What gives?  This seems 
>unintuitive to me.  Any thoughts?
>
>Thanks,
>Oliver
>
>
>