From: Brian Candler <b.candler@...>
Date: 2011-01-04T23:32:49+09:00
Subject: Re: Is singleton class of an object already created?

Samnang Chhun wrote in post #972157:
> I would like to know is there any ways to check is singleton class of an
> object already created?
>
> ex: obj.singleton_class_defined?

As an indirect test, you can't Marshal any object with a singleton class 
(although there are other kinds of object that you can't Marshal either)

irb(main):001:0> foo = "abc"
=> "abc"
irb(main):002:0> (Marshal.dump(foo) && false) rescue true
=> false
irb(main):003:0> def foo.zzz; end
=> nil
irb(main):004:0> (Marshal.dump(foo) && false) rescue true
=> true

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