From: dblack@...
Date: 2006-10-06T20:42:45+09:00
Subject: Re: nil being empty

Hi --

On Fri, 6 Oct 2006, David Chelimsky wrote:

> On 10/5/06, Ohad Lutzky <lutzky@gmail.com> wrote:
>> Show of hands - who thinks this is bad form?
>> 
>> class NilClass
>>   def empty?; true; end
>> end
>
> Doesn't it depend on context? The other responders seem to suggest
> that is objectively bad form, with which I  can agree (generally), but
> in a case like this:
>
> collection.select do |item|
> item.respond_to?(:empty?) and (!item.empty?)
> end
>
> I might prefer
>
> collection.select do |item|
> true unless item.empty?
> end
>
> or this (which, though more terse, I personally find less readable)
>
> collection.select do |item|
> !item.empty?
> end

(Don't forget Enumerable#reject :-)

But "empty" actually means something, and it doesn't apply to all
objects.  (I mean, it *can*, if you define it, but it doesn't make
sense.)  I wouldn't know whether any of these objects were or were not
empty:

   10
   98.6
   String
   lambda { puts "hi" }

etc.  nil is in that category.


David

-- 
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org