From: Wilson Bilkovich <wilsonb@...>
Date: 2006-10-30T14:24:28+09:00
Subject: Re: how to reset and how to undefine a class

On 10/30/06, Adriano Mitre <adriano.mitre@gmail.com> wrote:
> Does any one know how to reset a class in Ruby? Subsequent class
> definitions don't replace the original, but are tipically appended to
> it.
>
> The following example is typical.
>
> #########################
> class Song
>   def play
>     puts "playing..."
>   end
> end
>
> s = Song.new
>
> class Song
>   def stop
>     puts "stopped."
>   end
> end
>
> s.play #=> "playing..."
> s.stop #=> "stopped."
> #########################
>
> How can I make s.stop produce a NoMethodError, ie., how can I reset Song
> class prior to redefining it?
>
> Besides, I would like to know how to undefine Song class, so that
> Song.new produce a NameError, i.e., behaving as if it were never
> defined.
>

The first question is (a little) straightforward, once you get a
handle on how open Ruby's classes are.
To remove the 'stop' method, 'reopen' the class as you did when adding
'stop' in the first place:

class Song
  undef stop
end

Removing the whole 'Song' constant is a little weirder. There is a
remove_const method, but you have to call it on the thing that
contains the constant you want to remove.
In this case, the thing above Song is Object.

Object.send(:remove_const, :Song)

Sorry for my poor explanation. Hopefully you won't need to do this
very often. I never have. Heh.