From: Ara.T.Howard@...
Date: 2005-04-30T04:44:29+09:00
Subject: Re: determining when inside 'class << self'

On Fri, 29 Apr 2005, Robert Klemme wrote:

> class Object
>   def inside_metaclass?() false end
> end
>
> class Class
>   def inside_metaclass?
>     begin
>       self.allocate
>       false
>     rescue TypeError => e
>       /virtual class/i =~ e.to_s and true
>     end
>   end
> end
>
> irb(main):058:0> class <<Object.new; p inside_metaclass? end
> true
> => nil
> irb(main):059:0> p inside_metaclass?
> false
> => nil
> irb(main):060:0> class String; p inside_metaclass? end
> false
> => nil
>
> Cheers
>
>    robert

hmm.  i like this more than the pure matching version - which seemed a bit
fragile.

seems like i could do

   harp:~ > cat a.rb
   class Object
     def inside_metaclass?
       begin
         allocate()
         false
       rescue NoMethodError
         false
       rescue TypeError => e
         %r/virtual class/i =~ e.to_s and true
       end
     end
   end

   obj = Object::new
   klass = Class::new

   p inside_metaclass? #=> false

   class << obj
     p inside_metaclass? #=> true
   end

   class << klass
     p inside_metaclass? #=> true
   end

   class << self
     p inside_metaclass? #=> true
   end


   harp:~ > ruby a.rb
   false
   true
   true
   true

too.

now - any opinions on whether this violates POLS or not:


#
# my attributes module - hoping to become a collection of better 'attr' like
# metamethods...
#
   require 'attributes'

   class C

   #
   # define a class attr => used like C::foo
   #
     class_attribute 'foo'

   #
   # define an instance attr => C::new.bar
   #
     attribute 'bar'

     class << self
     #
     # define a class attr => used like C::foobar
     #
     # note that this would be the SAME as using class_attribute 'foobar'
     # outside of metaclass
     #
       attribute 'foobar'
     end

   end

so, you see, Object::attribute would be context sensitive to being inside a
metaclass or not - if inside a Class.metaclass it's defining a class
attribute, else an instance attribute.

thoughts?

-a
-- 
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