From: George Koehler <xkernigh@...>
Date: 2011-11-24T11:34:23+09:00
Subject: [ruby-core:41274] [ruby-trunk - Feature #5582] Allow clone of singleton methods on a BasicObject


Issue #5582 has been updated by George Koehler.


=begin
My first attempt:

 module Clone
   include Kernel
   (instance_methods - [:clone, :initialize_clone]).each {|m| undef_method m}
 end
 
 b = BasicObject.new
 class << b
   include ::Clone
   def single; "Quack!"; end
 end
 
 c = b.clone
 puts c.single

Output:

 scratch.rb:3: warning: undefining `object_id' may cause serious problems
 Quack!

Clone inherits from Kernel, but undefines all its instance methods except Clone#clone and Clone#initialize_clone. This technique has some awful side effects: Kernel === b and Kernel === c become true. Clone might inherit metamethods from Kernel (because I only undefined instance methods, not metamethods).
=end

----------------------------------------
Feature #5582: Allow clone of singleton methods on a BasicObject
http://redmine.ruby-lang.org/issues/5582

Author: Simon Chiang
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 1.9.2


Currently I do not know of a way to implement something like 'clone' on a BasicObject subclass.  This is as close as I've gotten but as you can see the singleton methods are not propagated to the clone.   

    require 'test/unit'

    class Context < BasicObject
      def _singleton_class_
        class << self
          SINGLETON_CLASS = self
          def _singleton_class_
            SINGLETON_CLASS
          end
        end
        _singleton_class_
      end

      def _class_
        _singleton_class_.superclass
      end

      def _extend_(mod)
        mod.__send__(:extend_object, self)
      end

      def _initialize_clone_(orig)
        # set variables as needed
      end

      def _clone_
        clone = _class_.allocate
        clone._initialize_clone_(self)
        _singleton_class_.included_modules.each {|mod| clone._extend_ mod }
        clone
      end
    end

    class ContextTest < Test::Unit::TestCase
      module A
        def a
          :a
        end
      end

      def test__clone__inherits_modules
        context = Context.new
        context._extend_ A
        clone = context._clone_
        assert_equal :a, clone.a
      end

      def test__clone__inherits_singleton_methods
        context = Context.new

        def context.a
          :a
        end

        clone = context._clone_
        assert_equal :a, clone.a  # fails
      end
    end

Is there a way to do this that I don't see? If not, then I request that a way be added - perhaps by allowing the singleton_class to be set somehow.

In my case I am using Context as the context for a dsl where methods write to a target (an instance variable).  I want to be able to clone a context such that I can have multiple contexts with the same methods, including extensions and singletons, that write to different targets.

Thank you.


-- 
http://redmine.ruby-lang.org