From: Robert Klemme <bob.news@...>
Date: 2005-11-10T23:37:13+09:00
Subject: Re: Numeric <=>

daz wrote:
> Robert Klemme wrote:
>> daz wrote:
>>>
>>> but it's able to tell that a == c which might
>>> be enough to keep a routine running.
>>
>> Definitely not:
>>
>>>> ar=(0..2).map { Roo.new }
>> => [#<Roo:0x101957e8>, #<Roo:0x101957b8>, #<Roo:0x10195788>]
>>>> ar.sort
>> ArgumentError: comparison of Roo with Roo failed
>
>
> Those instances are all different.  The change only helps
> by detecting equality, which is possible when a == a:

But for detecting equality there's already == and eql?.  And these methods
are used where equality is needed (namely in a hash).  No need to have a
crippled <=>.

>   class Roo < Numeric; end
>   a = Roo.new
>   p [a,a].sort  # [#<Roo:0x264a66c>, #<Roo:0x264a66c>]
>
> - Better than:
>     "I can't sort these, I don't know what they are."

I beg to differ: IMHO it's better to make this case raise an error because
that way it's more likely that a missing implementation of <=> is
detected.

>>>  * numeric.c (num_cmp): added to satisfy Comparable assumption.
>>
>> Hm...  Doesn't sound as if the assumption was satisfied...
>>
>
> Nothing deep here, I think - just a tiny kink removed :-?

Kind regards

    robert