Test whether a Ruby class is a subclass of another class?

Question

I would like to test whether a class inherits from another class, but there doesn't seem to exist a method for that. class A end class B < A end B.is_a? A => false B.superclass == A => trueA trivial implementation of what I want would be: class Class def is_subclass_of?(clazz) return true if superclass == clazz return false if self == Object superclass.is_subclass_of?(clazz) end endbut I would expect this to exist already.

Answer 1

You could define this yourself pretty easily--but keep in mind class can inherit from clazz without clazz being the direct superclass of class. For example, most things in Ruby inherit from Object, but for example Array inherits from both Enumerable and also from Object. How can you be sure you're getting the right thing?

If you want to check whether class inherits from clazz at all, try:

def inherits_from?(sub, sup)

  sub.ancestors.include?(sup)

end

puts(inherits_from?(Array, Enumerable))

puts(inherits_from?(Array, Object))

This will print True twice, since the Array class includes the ancestor classes Object *and* Enumerable