[ruby-core:50826] [ruby-trunk - Feature #5582] Allow clone of singleton methods on a BasicObject

Issue #5582 has been updated by nobu (Nobuyoshi Nakada).


=begin
2.0 allows `method transplanting'.

  module Clone
    %i[clone initialize_copy initialize_dup initialize_clone].each do |m|
      define_method(m, Kernel.instance_method(m))
    end
  end
=end

----------------------------------------
Feature #5582: Allow clone of singleton methods on a BasicObject
https://bugs.ruby-lang.org/issues/5582#change-34663

Author: thinkerbot (Simon Chiang)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: 
Target version: next minor


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.


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