From: "Ara.T.Howard" <ahoward@...>
Date: 2004-08-11T06:11:15+09:00
Subject: Re: empty? and size in Enumerable

On Tue, 10 Aug 2004, Martin DeMello wrote:

> Robert Klemme <bob.news@gmx.net> wrote:
>> "Martin DeMello" <martindemello@yahoo.com> schrieb im Newsbeitrag
>>>
>>> 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
>
> My concern was if #each created a temporary data structure in O(n) time
> (e.g. an ordered hash) - this would make sense for #each, since its
> running time is O(n) anyway, but would be a large hit for empty?

my concern would be for code that created a temporary data structure to
iterate - the designer should re-design!  ;-)  seriously, the rbtree package
from the raa works exactly like an ordered hash and it does not do this - i
would say it's a serious flaw if an ordered container cannot iterate itself in
order w/o creating temp structures - though your point is well taken and
correct.


-a
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