From: Manuel Kasten <kasten.m@...>
Date: 2005-11-10T16:57:13+09:00
Subject: Re: Question regarding <=> operator and Comparable Mixin

Yukihiro Matsumoto schrieb:
> Hi,
> 
> In message "Re: Question regarding <=> operator and Comparable Mixin"
>     on Thu, 10 Nov 2005 02:27:12 +0900, Manuel Kasten <kasten.m@gmx.de> writes:
> 
> |But if I return nil (just like Integer <=> String) <= is fine [line 
> |009], but == behaves differently from what I expected. Why doesn't [line 
> |11] return false like [line 10] does? I thought == is supposed to return 
> |true or false, nothing else?
> 
> "nil" denotes underlying assumption (<=> to return an integer value)
> is not met.  Ruby sometimes use nil as a small error indicator.
> 
> 							matz.

Hi,

then why doesn't [line10] return nil? a <=> b is nil [6], so is c <=> d [7].
a == b returns false [10], while c == d returns nil [11]. I expected 
both to return nil or both to return false.

Thanks for your help,

Manuel Kasten


irb(main):002:0> a = 5
=> 5

irb(main):003:0> b = "Hallo"
=> "Hallo"

irb(main):004:0> c = Modnum.new(3,7)
=> #<Modnum:0x101ae1c8 @base=7, @value=3>

irb(main):005:0> d = Modnum.new(3,9)
=> #<Modnum:0x101a6c20 @base=9, @value=3>

irb(main):006:0> a <=> b
=> nil

irb(main):007:0> c <=> d
=> nil

irb(main):010:0> a == b
=> false

irb(main):011:0> c == d
=> nil