> I would like to know is there any ways to check is singleton class of an
> object already created?

Perhaps you need a method to determine the presence of singleton
methods. In Ruby 1.9.2 you have the Object#singleton_methods that
returns an array of singleton methods defined on the object.

Flanagan, and Matz's book always talks about "opening" the eigenclass,
and not defining one. I guess that a singleton class always exists for
an object, whether a singleton method for that object exists or not.
You can always get a reference to the eigenclass of the object with
"class << object; self; end", where object can be any object (that
allows singleton methods to be defined on them).

--
Anurag Priyam