From: Robert Klemme <shortcutter@...>
Date: 2010-08-15T19:35:13+09:00
Subject: Re: kind_of?( NilClass )

On 14.08.2010 22:02, Philipp Kempgen wrote:
> Should I write
> 	var.kind_of?( NilClass )
> or simply
> 	var == nil
> ?
>
> I have the feeling that kind_of?(NilClass) is more "proper"/"clean"
> but then again it decreases the readability and might not even be
> necessary.

The other suggested checks are cleaner IMHO.  There is only ever one 
instance of NilClass (see below) so you can immediately check against 
that or use method #nil?.

You cannot create other instances:

irb(main):001:0> NilClass.new
NoMethodError: undefined method `new' for NilClass:Class
         from (irb):1
         from /usr/local/bin/irb19:12:in `<main>'
irb(main):002:0> NilClass.allocate
TypeError: allocator undefined for NilClass
         from (irb):2:in `allocate'
         from (irb):2
         from /usr/local/bin/irb19:12:in `<main>'
irb(main):003:0>

> Are there any situations where it makes sense to subclass NilClass?

Unlikely.

So, in an attempt to sum this up.  This is what you can do ordered from 
what I'd consider most reasonable to least reasonable:

if var.nil? # test for identity
if var == nil # test for equivalence
if var.equal? nil # test for identity
unless var # note: will also catch false
if NilClass === var # superfluous type check
if var.kind_of? NilClass # superfluous type check

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/