From: Loren Segal <lsegal@...>
Date: 2011-01-24T05:09:50+09:00
Subject: [ruby-core:34807] Re: [Ruby 1.9-Bug#4307][Open] include fails after undef_method



On 1/23/2011 2:14 PM, Adriano Mitre wrote:
> After using #undef_method on a method "inherited" from a mixin, reincluding the mixin should redefine it, but that is not what happens.
>

This seems like expected behaviour to me.

Calling #undef_method inside a class marks that method as uncallable in 
the class itself. Module inclusion only affects method lookup through 
the inheritance tree, it doesn't actually copy methods onto the class. 
Therefore, your Array class is saying: "I will no longer accept method 
calls to 'foo'". Reincluding (or including another module) does not 
change the fact that Array is still blocking any calls to 'foo', it only 
changes the inheritance tree. This is actually well documented:

http://rubydoc.info/stdlib/core/1.9.2/Module:undef_method

The only way to remove this "undef" is to define the method directly on 
the class, not through an included module. You can also look at 
`remove_method` (documented in above link) which will continue to look 
for a method in the inheritance tree even if removed directly on the 
class. Note that this would require the original method to be defined on 
the class itself, not through inclusion (which is not how your example 
works).

The other issue with your example is that re-including an already 
included module is effectively a noop:

     module Foo
       def foo; 42 end
     end

     class MyClass
       include Foo; p ancestors
       include Foo; p ancestors
     end

     # => [MyClass, Foo, Object, Kernel]
     # => [MyClass, Foo, Object, Kernel]