From: Rick DeNatale <rick.denatale@...>
Date: 2007-11-17T01:30:59+09:00
Subject: Re: What is the correct way to check for existence of virtual class?

On Nov 16, 2007 8:47 AM, Voroztsov Artem <artem.voroztsov@gmail.com> wrote:
> One can write:
>
>   class Object
>     def singleton_class
>       class <<self;  self; end rescue nil
>     end
>   end
>
>   puts "aaa".singleton_class
>   puts 8.singleton_class
>
> Is it the assumed way to do the job?

There's a bit of a Heisenberg problem here, in that the act of
measuring alters the result.

Singleton instance classes aren't created until they are needed, but
one of the things which creates them is class <<x;end so you're really
not checking whether or not the singleton class already exists this
way.

Another way would be

   !var.singleton_methods.empty?

BTW, your 8.singleton_class will fail, Fixnums can't have singleton classes.

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/