Question

Say you are overwriting a method in a subclass with a different arity:

class A
  def foo(arg)          # arity is 1
    # doing something here
  end
end

class B < A
  def foo(arg1, arg2)   # arity is 2
    super(arg1)         # <- HERE
  end
end

Is there a way to get the arity of super on line HERE?

(The real use case: I’m calling super knowing that the superclass doesn’t take any arguments. However, if the superclass implementation (in a gem) ever changes, I’d like to issue a warning.)

Thanks for your help!

Answer 1

Regarding your real use case: there’s no need to check the arguments yourself. Just call

super(arg1)

and Ruby will raise an ArgumentError if the argument count doesn’t match.

Update

Due to some downvotes, I think I should answer your initial question.

How to get the arity of “super”?

Starting with Ruby 2.2, there’s Method#super_method and UnboundMethod#super_method:

class A
  def foo(arg)
  end
end

class B < A
  def foo(arg1, arg2)
  end
end

B.instance_method(:foo).arity #=> 2
B.instance_method(:foo).super_method.arity #=> 1

From within B#foo, you could write:

class B < A
  def foo(arg1, arg2)
    method(__method__).super_method.arity #=> 1
  end
end