From: Trans <transfire@...>
Date: 2007-01-24T02:35:22+09:00
Subject: Re: Hash pairs at?


Ken Bloom wrote:
> On Mon, 22 Jan 2007 05:58:25 +0900, dblack wrote:
>
> > Hi --
> >
> > On Mon, 22 Jan 2007, Joel VanderWerf wrote:
> >
> >> gga wrote:
> >>> dblack@wobblini.net wrote:
> >>>
> >>>> It's not incorrect or buggy; that's the way Enumerable#find_all works.
> >>>> In addition to being Enumerables themselves, arrays serve as the
> >>>> common container for the results of lots of different Enumerables.
> >>>>
> >>>
> >>> Sorry, David, but I disagree.  It may not be buggy (as the bugginess is
> >>> properly documented :), but it is certainly incorrect.  Re-read my
> >>> post.
> >>> Hash.reject, which is also an Enumerable, DOES return a hash.
> >>> Hash.find_all which is algorithmically the same as Hash.reject but
> >>> without a negation, does not.
> >>> Someone forgot to override find_all in the Hash case, but did remember
> >>> to do it for Hash.reject.  Or, if you are of the belief that indeed
> >>> Enumerables should always return an array, Hash.reject was incorrectly
> >>> overridden when it shouldn't have been.
> >>
> >> This does look a bit odd...
> >>
> >> irb(main):001:0> h = {1=>3, 5=>7}
> >> => {5=>7, 1=>3}
> >> irb(main):002:0> h.reject {|k,v| k==1}
> >> => {5=>7}
> >> irb(main):003:0> h.select {|k,v| k==1}
> >> => [[1, 3]]
> >
> > A bit.  The funny thing, though, is that it of course makes it
> > possible to do either -- so the irregularity actually provides a kind
> > of resilience.  The consistent version, should it ever come into
> > being, will shut the door on one of them.
> >
> > I know that people don't want to do select { not } and so on... so
> > I can see that it's not really ideal.  But it's kind of fascinating
> > that "fixing" it, in either direction, would result in a net loss of
> > functionality.
>
> No it wouldn't because you could just call .to_a on the returned hash to
> get the nested array representation.

that's a good point.

the downside however is that we would always have to use #to_a to
ensure polymorphism between assoc array and hash. so it's a bit of an
anti-duck. (array doesn't have a reciporcal #to_h either btw, though
that would be nice in itself!)

T.