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On 5/28/06, Kevin Olbrich <kevin.olbrich / gmail.com> wrote:
>
> I think I may have stumbled upon a minor bug in ranges.
>
>
> on my system,
>
> ("Z".."AA").map returns []
>
> while
>
> "Z".succ returns "AA"
>
> "Z".upto("AA") also returns []
>
> ruby 1.8.4 (2005-12-24) [i686-darwin8.6.1]
>
> Is this a real bug, or am I expecting behavior that really shouldn't be
> there?
>
> _Kevin
>
> --
> Posted via http://www.ruby-forum.com/.
>
>
By looking at the definition of the Range class
http://www.ruby-doc.org/core/classes/Range.html
- please note that x..y is the same as Range.new(x,y) -
one can conclude that Ranges are constructed using <=> and .succ.
While it is true that "Z".succ == "AA" it is also true that "Z" <=> "AA" is
implying "Z">"AA" and
therefore Range("Z".."AA") seems correctly empty.


What might come as a surprise is that you have found a ruby object that is
greater than its successor but that depends on the kind of *order* we are
dealing with. This oddness comes from String, not from Range though. By
carefully looking at the definition of succ and <=> in String one can ask
oneself if constructing Ranges from Strings is very useful in all contexts
because <=> and succ do not seem to be desinged for the same view of the
String domain.

BTW what do you think ("AA".."Z").to_a delivers (should be infinite by the
same reasoning, should it not?).

It seems therefore that some classes are not made to be used for Ranges
although they are Compareable and Enumerable which is not very reassuring. I
guess you just opened Pandorra's can :(

Maybe that is because it was not clear that "<=>" and "succ" depend on each
other by the design of  the language and as they are used for other things
"<=>" for Compareable one could argue that we have too closely coupled
bahvior here. And while one could argue so, I do! Different methods should
be used to define Range (e.g. range_smaller?, range_next).


Cheers
Robert

-- 
Deux choses sont infinies : l'univers et la bóŐise humaine ; en ce qui
concerne l'univers, je n'en ai pas acquis la certitude absolue.

- Albert Einstein

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