Issue #8297 has been updated by nobu (Nobuyoshi Nakada). Description updated ---------------------------------------- Bug #8297: extend & inherited class variable issue https://bugs.ruby-lang.org/issues/8297#change-38757 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. -- http://bugs.ruby-lang.org/