From: Ryan Leavengood <mrcode@...>
Date: 2005-05-08T02:26:37+09:00
Subject: Re: Prove me Wrong! Re: RCR 303: nil should accept missing methods

Ryan Davis wrote:
> 
> On May 5, 2005, at 8:39 PM, John Carter wrote:
> 
>> If I prove wrong, I will gladly retract my RCR and apologise.
> 
> 
> The burden of proof (that this is needed) must sit on you, not on us  
> (that this is not needed).

I agree. In fact, to quote 
http://www.adamsmith.org/logicalfallacies/000656.php

"Shifting the burden of proof is a specialized form of the argumentum ad 
ignorantiam. It consists of putting forward an assertion without 
justification, on the basis that the audience must disprove it if it is 
to be rejected. Normally we take it that the new position must have 
supporting evidence or reason adduced in its favour by the person who 
introduces it. When we are required instead to produce arguments against 
it, he commits the fallacy of shifting the burden of proof."

I feel this discussion has been useful, and the NullObject pattern is 
interesting, but I'm in the camp that this will do more harm than good. 
To shift the burden of proof to us only tends to deflate your own 
argument through logical fallacy.

Most useful programs interact with other outside programs, or of course 
with a user. Using this pattern would cause silent errors that would 
frustrate users and possibly crash other applications (as in Austin 
Ziegler's PDF::Writer example.) If a user of some Rails application asks 
to see some important bit of information, and gets nothing instead, due 
to nil eating the "show_me_the_important_stuff" method, the user will 
not be happy. And the developer will have to spend time figuring out why 
the information was blank (which could be for any number of reasons 
besides the nil-monster.)

Ryan