But I got the error like this:
in test': undefined methodinclude’ for #QQ:0x2bb5150
(NoMethodError)
Call it on the class instead, as in self.class.include QQ_Elem.
However, since it’s only supposed to be called from within the class
itself (not an instance of the class), it’s marked as private. To
circumvent this, call self.class.send :include, QQ_Elem.