From: Jason Mayer <slamboy@...>
Date: 2007-01-30T21:53:34+09:00
Subject: Re: Decending Range

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On 1/30/07, Dominic Marks <dom@helenmarks.co.uk> wrote:
>
> Hello,
>
> I was surprised of to find this behaviour:
>
> irb(main):008:0> a, b = 1, 100
> => [1, 100]
> irb(main):009:0> (a..b).to_a.length
> => 100
> irb(main):010:0> (b..a).to_a.length
> => 0
>
> Now I am aware that only a simple .reverse is required to work
> around this but this seemed a little un-ruby like. Is there
> some thoughtful reason to not have ranges in both
> directions that I'm missing?
>
> Cheers,
> Dominic

Hrm.

irb(main):001:0> a,b = 1,100
=> [1, 100]
irb(main):002:0> ar = Array.new
=> []
irb(main):003:0> ar1 = Array.new
=> []
irb(main):004:0> ar = (b..a).to_a
=> []
irb(main):005:0> ar1 = (100..1).to_a
=> []
irb(main):006:0> b.downto(a) { |x| ar1.push(x) }
=> 100
irb(main):007:0> p ar1
[100, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83,
82, 81
, 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63,
62, 61
, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45, 44, 43,
42, 41
, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23,
22, 21
, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

 I thought that ranges worked the way you did, until I looked it up:
http://www.ruby-doc.org/core/classes/Range.html

Ranges can be constructed using objects of any type, as long as the objects
can be compared using their <=> operator and they support the succ method to
return the next object in sequence.
So, it looks like 100..1 won't work because

irb(main):001:0> 100.succ
=> 101

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