From: Brian Guthrie <bguthrie@...>
Date: 2006-08-03T23:58:04+09:00
Subject: Re: A left-exclusive Range class

Brian Guthrie wrote:
> Cyrus Hall wrote:
>> The current Range class in ruby is quite useful, however, I was recently
>> trying to capture a simple algorithm and ended up needing to express
>> left-exclusion.  This is the one feature ruby currently does not support
>> in its Range class.
>>
>> I did some digging into 1.8.4's Range implementation and it appears
>> that the changes needed to support left-exclusion would be minimal.
>> Rather, the problem seems syntactical.  Currently '..' and '...' are
>> used to represent right-inclusion and -exclusion, respectively.  This
>> syntax clearly can not be extended to left-exclusion.  There appears to
>> have been a related debate about this on ruby-talk back in Oct. 2004,
>> with the conclusion being, to paraphrase the entire discussion, "this is
>> hard, lets forget about it for now."
>> Has this been discussed since 2004?  Would people be interested in
>> finding a way to get left-exclusion into the Range class?  This may be
>> something that has been addressed in all the language work going into
>> 1.9/2.0, and if so, any pointers would be greatly appreciated.
>>
>> Ciao,
>> Cyrus Hall
> 
> You could try just appropriating a different piece of syntax and using 
> it for your own evil purposes, e.g. <<
> 
> class Fixnum
>   def <<(number)
>     (self + 1)..number
>   end
> end
> 
> for i in 1<<10
>   # i starts at 2
> end
> 
> Brian Guthrie
> 

Of course by doing that you've totally just broken the existing 
Fixnum#<<. Bummer, should've checked first.  Ah, well.

Brian Guthrie