Issue #8297 has been reported by dunric (David Unric).

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Bug #8297: extend & inherited class variable issue
https://bugs.ruby-lang.org/issues/8297

Author: dunric (David Unric)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 
ruby -v: 2.0.0p0
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN


=begin
By the current documentation, Object#extend method has to (only) add instance methods of a module given as a parameter.
In the following example, the class ((*C*)) is extended with module ((*M*)).
By ((*class_variables*)) method sent to singleton class of C also did inherit class variable ((*@@xyz*)).
However when inherited ((*@@xyz*)) is accessed, ((*NameError*)) exception is raised as it is was not initialized.

(({module M
      @@xyz = 123
end
M.class_variables    # [:@@xyz]
M.class_variable_get :@@xyz    # 123 , so far so good

class C
      extend M
end
((*p C.singleton_class.class_variables    # [:@@xyz]
p C.singleton_class.class_variable_get :@@xyz # NameError exception*))
}))

Either ((*class_variables*)) returns invalid array - ie. ((*@@xyz*)) was not inherited at all or ((*class_variable_get*)) ignores class variables inherited from module (when sent to a singleton).
=end
Prior Ruby versions like 1.9.3p392 does not suffer this issue as return with Module#class_variables returns an empty array.



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