unextend a module | ruby-talk-183401

dup.rb

# http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/183650
# Have you tried #dup?

module Actor
   def work
     "actor"
   end
end

module Waiter
   def work
     "waiter"
   end
end

class Human; end

dirk = Human.new
dirk.extend Actor
p dirk.work

begin
dirk = dirk.dup
p dirk.work
rescue
   puts "dirk has no job"
end

dirk.extend Waiter
p dirk.work

__END__

# DRY RUN
"actor"
dirk has no job
"waiter"

And, to put it in the nice #unextend method:

class Object
   def unextend
     self.replace dup
   end
end

module Actor
   def work
     "actor"
   end
end

module Waiter
   def work
     "waiter"
   end
end

class Human; end

dirk = Human.new
dirk.extend Actor
p dirk.work

begin
dirk.unextend
p dirk.work
rescue
   puts "dirk has no job"
end

dirk.extend Waiter
p dirk.work

% ruby unextend
"actor"
dirk has no job
"waiter"

quasiextender.rb

# http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/183401
require 'delegate'
module QuasiExtender
   def quasi_extend(mod)
     @__quasi_extensions ||= []
     @__quasi_extensions << mod
   end

   def quasi_retract(mod)
     @__quasi_extensions ||= []
     @__quasi_extensions.delete_if { |ext| ext == mod }
   end


   def method_missing(name, *args, &block)
     @__quasi_extensions ||= []
     meth = nil
     found_mod = nil
     @__quasi_extensions.each do |ext|
        begin
          meth = ext.instance_method(name.to_sym)
          found_mod = ext
        rescue NameError, NoMethodError
          next
        else
          break
        end
     end

     if meth.nil? # we didn't find it
        super
     else
        sneaky_class = Class.new(SimpleDelegator) {
                 include(found_mod)
        }
        sneaky_obj = sneaky_class.new(self)

        meth.bind(sneaky_obj).call(*args, &block)
     end
   end
end

quasiextender_irb_session.txt

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/183401

Subject: Re: unextend ?
From: Logan Capaldo <logancapaldo gmail.com>
Date: Fri, 10 Mar 2006 06:36:23 +0900
References: 183334
In-reply-to: 183334

On Mar 9, 2006, at 11:03 AM, Dirk van Deun wrote:

> A very short and simple question: is there a function to "unextend" an
> object ?  Obviously it does not exist under that name, nor could I  
> find
> anything like it.  It would be useful though to do "traits":
>
> dirk = Human.new
> dirk.extend(actor)
> dirk.work
> if dirk.income < PITTANCE
>   dirk.unextend(actor)
>   dirk.extend(waiter)
>   dirk.work
> end
>
> Dirk van Deun
> -- 
> Ceterum censeo Redmond delendum
>

I don't believe there is an unextend method, however if you're  
willing to live with some dark magic that I haven't extensively tested:

irb(main):001:0> require 'quasiextender'
=> true
irb(main):002:0> class A
irb(main):003:1>  def each
irb(main):004:2>   yield 1
irb(main):005:2>  end
irb(main):006:1>  include QuasiExtender
irb(main):007:1> end
=> A
irb(main):008:0> a = A.new
=> #<A:0x370718>
irb(main):009:0> a.quasi_extend(Enumerable)
=> [Enumerable]
irb(main):010:0> a.map { |x| x.to_s }
=> ["1"]
irb(main):011:0> a.quasi_retract(Enumerable)
=> []
irb(main):012:0> a.map { |x| x }
NoMethodError: undefined method `map' for #<A:0x370718  
@__quasi_extensions=[]>
         from ./quasiextender.rb:30:in `method_missing'
         from (irb):12

And here's the evil code. Its actually not terribly long: (in quasiextender.rb)