From: "David N. Springer" <springer@...>
Date: 2004-10-01T00:55:30+09:00
Subject: Re: Range syntax theory

Austin Ziegler wrote:

>On Thu, 30 Sep 2004 22:58:26 +0900, Henrik Horneber <ryco@gmx.net> wrote:
>  
>
>> From an intellectual point I sort of understand the '..' and '..'
>>notation. What distracts me most, is the visual difference ... that the
>>visually longer three dot form contains fewer elements than the shorter
>>two dot form.
>>
>>(1..5).to_a
>>=>[1,2,3,4,5]
>>(1...5).to_a
>>=>[1,2,3,4]
>>    
>>
>
>That's a dangerous consideration -- and not always true:
>
>irb(main):001:0> (1..5).include?(4.99)
>=> true
>irb(main):002:0> (1...5).include?(4.99)
>=> true
>irb(main):003:0>
>
>1...5 doesn't include only the numbers 1, 2, 3, and 4 -- it contains
>the infinities between the numbers, and the infinity between 4 and 5,
>but not 5 itself.
>
>-austin
>  
>
I see the distinction but a some point the reality of the limits of the 
internal representation lets us down:

irb(main):001:0> (1...5).include?(4.999999999999999)
=> true
irb(main):002:0> (1...5).include?(4.9999999999999999)
=> false
irb(main):003:0> 4.999999999999999 < 5
=> true
irb(main):004:0> 4.9999999999999999 < 5
=> false
irb(main):005:0>

-- 
David N. Springer