From: Bill Kelly <billk@...>
Date: 2005-05-07T13:35:21+09:00
Subject: Re: RCR 303: nil should accept missing methods and return nil

From: "John Carter" <john.carter@tait.co.nz>
>
> Prove me wrong, take the challenge.
> 
> Next time your pet program dies of a NoMethodError for NilClass add
> 
> class NilClass
>    def method_missing(sym,*args)
>      nil
>    end
> end
> 
> ...at the head of your program.
> 
> See empirically what happens. Does it hide bugs? Does it just work? Does 
> it still throw an exception or give an error message?

A CGI script I coded a couple weeks ago just got:

  [Fri May 06 20:22:37 PDT 2005] Process 27695 encountered
  #<NoMethodError: undefined method `[]' for nil:NilClass>
   at /var/www/---------.net/www/quake/servers/list.cgi:133:in `top_client'

and indeed, when I added method_missing to NilClass the bug
was masked and the script executed without complaint.

Interesting . . . 

The bug was something in an as-yet untested "else" case
in the code.  Something a unit test should have caught,
if i'd written any for this quick hack..... which I didn't.

I would count myself in the "fail as early as possible"
camp.  I still don't like that NilClass#method_missing
masks the bug... but it did prevent the error in this
case from the user's point of view.

If I were to consider adding NilClass#method_missing
permanently to my script(s), I would at least cause it
to write the problem and stack trace to a logfile, so
that I could periodically scan the logfile for any such
incidents.

Interesting challenge though, thanks ...  :)


Regards,

Bill