class - How can I reverse ruby's include function

Question

I'll explain what i'm looking for in code as thats probably the most succinct:

module Mixin
  def method
    puts "Foo"
  end
end

class Whatever
  include Mixin
end

w = Whatever.new
w.method
=> "Foo"

# some magic here
w2 = Whatever.new
w.method
=> NoMethodError

I had tried just undefining the Mixin module using remove_const, but this doesn't seem to make any difference to Whatever. I had assumed that #include just added a reference to the module into the class's method resolution chain - but this behaviour doesn't agree with that.

Can anyone tell me what include actually does behind the scenes, and how to reverse this?

Answer 1

As it seems probably you want to accomplish these on instances instead of the whole class, so I would change klochner's code a bit to handle just one instance instead of all the instances of a class.

module ModuleRemover

    def remove_module(mod, options = {})
      metaclass = class << self; self end
      mod.instance_methods.each {|method_name| metaclass.class_eval { undef_method(method_name.to_sym) }}
    end

end

As Mladen pointed out, it would be cool to avoid removing methods that are overwritten on the host class, so an [only, exclude] options for this method would be ideal.

>> c1 = C.new
>> c1.foo
=> fooing
>> c1.extend(ModuleRemover)
>> c1.remove_module(Mod)
>> c1.foo
=> NoMethodError: undefined method `foo' for #< C:0x11b0d90>
>> c2 = C.new
>> c2.foo
=> fooing