From: Jeff Mitchell <quixoticsycophant@...>
Date: 2004-05-09T06:23:12+09:00
Subject: Re: How to get the last 5 elements of an array?


--- Jeff Mitchell <quixoticsycophant@yahoo.com> wrote:
> 
> --- 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.

Whoa hang on, I didn't read the OP well enough.  At least x[-3..2]
should return [8, 9, 10, 1, 2, 3], otherwise this isn't even a
subset of modular arithmetic, it's something else.




	
		
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