Test Whether a Ruby Class Is a Subclass of Another Class
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 =>...
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
=> true
A 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
end
but I would expect this to exist already.
2 Answers
Just use the < operator
B < A # => true
A < A # => false
or use the <= operator
B <= A # => true
A <= A # => true
Also available:
B.ancestors.include? A
This differs slightly from the (shorter) answer of B < A because B is included in B.ancestors:
B.ancestors
#=> [B, A, Object, Kernel, BasicObject]
B < B
#=> false
B.ancestors.include? B
#=> true
Whether or not this is desirable depends on your use case.
Maya is a hardware enthusiast who tests and reviews smart home devices, smartphones, wearables, and audio gear. She focuses on practical consumer value and build quality.
