From: Jeff Mitchell <quixoticsycophant@...>
Date: 2004-05-09T05:46:52+09:00
Subject: Re: How to get the last 5 elements of an array?


--- David Alan Black <dblack@wobblini.net> wrote:
> Hi --
> 
> Gavin Sinclair <gsinclair@soyabean.com.au> writes:
> 
> > For example, consider this:
> > 
> >   x = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> >   x[-5..3]  # -> nil
> > 
> > If even *that* returns nil, when *all* numbers in the range are valid
> > indexes, then...
> > 
> > Also, there's everybody's favourite example:
> > 
> >   x[10..15] # -> []
> >   x[11..15] # -> nil
> > 
> > I'd rather see 'arr[range]' *always* return an array, no matter the
> > value of 'arr' and 'range'.
> 
> I guess it comes down to the necessity to translate between the very
> different perspectives of Arrays and Ranges when it comes to counting.
> For example, for a 5-element array, -3 > 1, counting Array-style.  I
> don't know whether there's a way to un-anomalize it; it may be one of
> these lumps that can be moved around under the carpet but is still
> always somewhere.  
> 

-3 == 2 > 1   (mod 5)

Yes the anomaly is that ruby only modularizes indices i for
-length <= i < length.  A purist might say modular arithmetic
should be applied globally or not at all, but this would give 

x[10..15] == x[20..25] == x[-20..-15] == [1,2,3,4,5,6]

which could fail to indicate Something's Wrong.  I see ruby's
subset of modular arithmetic as a middle ground between convenience
and saftey.  One can always write ModArray trivially, after all.




	
		
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