Suppose I want to determine if Admin inherits from ActiveRecord::Base. One way is to do this is Admin.new.kind_of? ActiveRecord::Base, but that instantiates an unused Admin object.
Is there an easy way of doing this without creating an Admin object?
Thanks
Sure, just compare the two classes:
if Admin < ActiveRecord::Base # ... end It is interesting to note that while Module#< will return true if Admin inherits from AR::Base, it will return false or nil if that's not the case. false means that it is the otherway around, while nil is for unrelated classes (e.g. String < Range returns nil).
It's pretty simple:
Admin < ActiveRecord::Base => true 
Class is derived from Module. ruby-doc.org/core-1.8.7/classes/Module.html#M000206Admin.ancestors.include? ActiveRecord::Base Hmm. Well, this works, but we've just learned a nicer way. It seems that Ruby's Module class defines an operator < for this purpose, and since class Class derives from Module, that means < will directly test for derived classes.
Admin.ancestors.includes? ActiveRecord::Base For direct ancestry you could also use
Admin.superclass == ActiveRecord::Base 
ActiveRecord::Base.