From: MonkeeSage <MonkeeSage@...>
Date: 2007-12-20T19:30:00+09:00
Subject: Re: String#[] behaviour

On Dec 19, 9:01 am, Pasha Nigerish <reed...@tut.by> wrote:
> Jordan Callicoat wrote:
> > Taking your example, "'asd'[-10..-1]", this means
> > 'asd'[-7..2] when you de-sugar it. Now in the other case,
> > "'asd'[0...10]", once you reach #length-1, you can stop and return
> > 0..#length-1. But with 'asd'[-7..2], what are you supposed to do when
> > the start index is less than the first index (0)? Well, you could skip
> > ahead to the first index, sure, but it makes just as much sense (if
> > not more) to return nil/empty string. Same goes for cases such as
> > 'asd'[-2..-3] (i.e., 'asd'[1..0]), where the start index is greater
> > than the end index.
>
> IMHO, the main goal of such a construct (some_string[-10..-1]) - to
> return last 10 chars from some_string. And in this case - returning
> 'asd' for 'asd'[-10..-1] seems to be as logical as returning 'asd' for
> 'asd' for [0..10] (as implemented now).
>
> right now (1.8.6) we have:
> 1) 'asd'[0..10] => 'asd'
> 2) 'asd'[2..1]  => ''
> 3) 'asd'[-1..-2] => ''
> -BUT-
> 4) 'asd'[-10..-1] => nil
>
> I think, that by a "Principle of Least Astonishment" (c) we can unify
> that cases - i.e. to return either 'asd' or nil in cases 1) and 4). All
> that we need - adjust start index of the range to 0, if negative - right
> after de-sugar.
> --
> Posted viahttp://www.ruby-forum.com/.

In thinking about it, I guess that does make some sense. Unless one
were to assume that negative starting indexes were more likely to be
programmer errors than larger-than-#length-1 end indexes (does anyone
claim this?), it seems to me that setting negative indexes to 0 would
be consistent with setting larger-than-#length-1 indexes to #length-1.
Maybe you should start an RCR for this.

Regards,
Jordan