From: Klaus Stein <usenet@...>
Date: 2005-05-19T19:20:14+09:00
Subject: Re: RCR 303: nil should accept missing methods and return nil

John Carter <john.carter@tait.co.nz> wrote:
> A very simple and generic way of improving the reliability of Ruby
> programs is to implement the NullObject pattern by allowing nil to
> accept all and every method instead of throwing a NoMethodError.
> 
As far as I understand the whole discussion some wish this behaviour to be
able to do things like

obj.meth1().meth2().meth3()

which should not break if meth2 for some cause returns nil.

On the other hand many people claim this will hide errors (I agree here).
It seems there are two kinds of nils: expected and unexpected ones.

So why dont we deal with the expected ones seperately:

==========================================================
class Object
  def nil_friendly
    self
  end
end

class NilClass
  def nil_friendly
    Blackhole.instance
  end
end

class Blackhole
   include Singleton
   def method_missing( sym, *args)
     nil
   end
end

## Now this works:

obj.meth1().meth2().nil_friendly.meth3()
==========================================================

So by inserting .nil_friendly (choose a better/shorter name for this) you
_explicitly_ tell that you don't care if nil ist returned.

This will not break any existing code, will not hide errors, but gives
shorter code without explicit ifs.

Comments?

Klaus Stein
-- 
http://lapiz.istik.de/

The Answer is 42. And I am the Answer. Now I am looking for the Question.