From: Pit Capitain <pit@...>
Date: 2007-03-14T00:38:47+09:00
Subject: Re: get object from its object-specific class?

Rick DeNatale schrieb:
> ObjectSpace.each_object(c2) {|o| p o}

Yeah Rick, this is what I came up with at first, too. But I didn't like 
  that it examines each Ruby object. Here's another solution, much 
uglier but also faster:

   def instance_of_singleton_class_1(sc)
     ObjectSpace.each_object(sc) do |obj|
       return obj
     end
   end

   def instance_of_singleton_class_2(sc)
     obj = nil
     sc.class_eval do
       if instance_methods(false).include?("singleton_method_added")
         org = instance_method("singleton_method_added")
         remove_method("singleton_method_added")
       end
       define_method("singleton_method_added") do |m|
         obj = self
       end
       remove_method("singleton_method_added")
       define_method("singleton_method_added", org) if org
     end
     obj
   end

Test that they both work the same:

   sc = class << {:a => 5}; self; end

   p instance_of_singleton_class_1(sc)  # => {:a=>5}
   p instance_of_singleton_class_2(sc)  # => {:a=>5}

And the benchmark:

   require "benchmark"

   Benchmark.bmbm do |bm|
     bm.report "ObjectSpace" do
       1000.times do instance_of_singleton_class_1(sc) end
     end
     bm.report "singleton_method_added" do
       1000.times do instance_of_singleton_class_2(sc) end
     end
   end

yields:

   Rehearsal ----------------------------------------------------------
   ObjectSpace              3.109000   0.000000   3.109000 (  3.188000)
   singleton_method_added   0.266000   0.000000   0.266000 (  0.265000)
   ------------------------------------------------- total: 3.375000sec

                                user     system      total        real
   ObjectSpace              3.016000   0.000000   3.016000 (  3.032000)
   singleton_method_added   0.266000   0.000000   0.266000 (  0.266000)

Regards,
Pit