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:

% cat quasiextender.rb
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