From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-05-05T09:24:48+09:00
Subject: Class#singleton_of


at the risk of totally annoying everyone on this list and not getting any real
work done for another day i'm posting some of the code i've scraped out of
this week's posts and throwing down a challenge to boot:

   jib:~/eg/ruby > cat a.rb
   class Class
     def singleton
       class << self; self; end
     end
     def singleton?
       not self.ancestors.include? self
     end
     def inside_singleton?
       singleton?
     end
     def singleton_of
       if singleton?
         m = %r/^(?:#<Class:)+(.*?)(>+)$/io.match inspect
           singleton_name, brackets = m[1], m[2]
           n = brackets.size - 1
           klass = klass_stamp singleton_name
           n.times{ klass = class << klass; self; end }
           klass
       else
         nil
       end
     end
     def klass_stamp hierachy
       relatives = hierachy.split %r/::/
       parent = Object
       while((child = relatives.shift))
         klass = parent.const_get child
         parent = klass
       end
       klass
     end
   end

   module M
     class C
       p singleton_of       # => nil
       class << self
         p singleton_of     # => M::C
         class << self
           p singleton_of   # => #<Class:M::C>
           class << self
             p singleton_of # => #<Class:#<Class:M::C>>
           end
         end
       end
     end
   end

   #
   # we now explode here
   #
   class << self
     p singleton_of
   end


   jib:~/eg/ruby > ruby a.rb
   nil
   M::C
   #<Class:M::C>
   #<Class:#<Class:M::C>>
   a.rb:28:in `const_get': wrong constant name #<Object:0xb7447a10 (NameError)
           from a.rb:28:in `klass_stamp'
           from a.rb:17:in `singleton_of'
           from a.rb:54


the challenge is obviously to implement Class#singleton_of without parsing the
output of inspect or, at least so that it works for all cases.  the return
value of Class#singleton_of ought to be pretty obivous - it's the thing on the
rhs of

   class << any_object

release the hounds!

-a
-- 
===============================================================================
| email :: ara [dot] t [dot] howard [at] noaa [dot] gov
| phone :: 303.497.6469
| renunciation is not getting rid of the things of this world, but accepting
| that they pass away. --aitken roshi
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