From: Robert Klemme <bob.news@...>
Date: 2004-08-10T18:36:15+09:00
Subject: empty? and size in Enumerable (was: Re: FirstEachLast, an extension to the Enumerable module.)


"Martin DeMello" <martindemello@yahoo.com> schrieb im Newsbeitrag
news:xW%Rc.68814$gE.48438@pd7tw3no...
> Robert Klemme <bob.news@gmx.net> wrote:
> >
> > Hm, sounds to me like it was not general enough to include it in
> > Enumerable.  Before I see that method I'd prefer to have size and
empty?
> > in Enumerable.  Just my 0.02 EUR...
>
> Can empty? be reliably implemented in terms of each for every
> enumerable? I can't think of an obvious problem with it, but that
> doesn't mean there isn't one.

Yes, that's possible IMHO.  My suggestion would be:

module Enumerable
  # O(1)
  def empty?
    each { return false }
    true
  end

  # O(n)
  def size
    inject(0) {|s,| s+1}
  end
end

Do you see any problems?  There's only the little disadvantage that size
is O(n) while there are most likely more efficient implementations for
certain collections.  But classes like Array and Hash provide their own
implementation anyway, which then overrides Enumerable#size.  So there's
no drawback IMHO, only the advantage that you don't have to write it if
you have a collection that can determine its size only via a complete
iteration.

Kind regards

    robert