From: listrecv@...
Date: 2005-11-14T07:57:15+09:00
Subject: Subclassing NilClass

I'd like to subclass NilClass, creating a NullCase, implementing in
Ruby a simple example of Martin Fowler's "SpecialCase" pattern (
http://patternshare.org/default.aspx/Home.MF.SpecialCase )

I'd like to subclass NilClass, so that the object returns false (and
nil? returns true).  But, I'd like to override method_missing so that
it returns the an instance of NullCase - not an exception, and not a
regular nil.

I had trouble subclassing NilClass - there's no new method - how do I
do this?


Basically, usage would be like

def a_method
  ...
  if condition
     x
  else
    NULL_CASE
  end
end

Later, you could do:
a = o.a_method
a.address.zip #--> No errors, just nil's

instead of
if a && a.address && a.address.zip
  a.address.zip
else
  nil
end

Please cc all responses to me at listrecv at gmail, thanks!