From: Pit Capitain <pit@...>
Date: 2006-08-15T02:13:56+09:00
Subject: Re: Calling non-existing methods works! (little magic??)

Martin S. Weber schrieb:
> I am kind of ... confused. Up till now I had the illusion you could only
> call methods on an object which you could also find via methods or via
> the included modules. Fine... Why does this output what it does then?
> Where is this method defined? Some kind of method lookup cache? How to
> force flushing it (besides redefining the methods of the receiver?)
> (...)

Martin, this seems to be a bug. As you guessed, there is a method lookup 
cache, and it isn't flushed correctly when removing a method. Here's a 
simpler code to show the bug...

Define a module, include it in a class and call a method of the module:

   module M
     def m
       p "M#m"
     end
   end

   class C
     include M
   end

   C.new.m
   # => "M#m"

Remove the method from the module:

   module M
     remove_method :m
   end

The method lookup cache of class C isn't cleared (bug), so you can still 
call the old method:

   C.new.m
   # => "M#m"

Here's one way to clear the method lookup cache for a given method: 
create an anonymous module and define a method with the same name:

   Module.new do
     def m
     end
   end

   C.new.m rescue p $!
   # => #<NoMethodError: undefined method `m' for #<C:0x2b83d10>>

I will forward this to the ruby-core mailing list.

Thanks for the bug report,
Pit