From: Rick DeNatale <rick.denatale@...>
Date: 2007-12-23T10:40:13+09:00
Subject: Re: Why is Array not Comparable

On Dec 22, 2007 8:17 PM, Martin Duerst <duerst@it.aoyama.ac.jp> wrote:
> I just bumped into this:
> Why does Array not include Comparable?
> Array defines <=>, and so including Comparable should be easy.
>
> It looks to me like a big oversight, or there must have been
> some very deep reasons to not do this, which I'm completely ignorant of.
>

Good question.

You can of course either open Array and include comparable, or extend
an individual array instance.

But some subtleties.

1) Just because Array implements <=> doesn't mean that it will work as
you expect for all arrays.   Array basically implements <=> by
comparing elements with the argument until either an element
comparison returns a non-zero or either the receiver or argument 'runs
out' of elements.

So if elements aren't comparable with <=> pairwise ...

2) Comparable not only requires that <=> be implemented but that it
return -1, 0, or 1.  Some classes implement it to return nil if the
argument isn't of the right class, so even if Array included
comparable things like ["a] < [1] wouldn't work.


-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/