bind

class A
  def test
    puts "In test, class = #{self.class}"
  end
end
class B < A
end
class C < B
end

um = B.instance_method(:test)
bm = um.bind(C.new)
bm.call
bm = um.bind(B.new)
bm.call
bm = um.bind(A.new)
bm.call

In test, class = C
In test, class = B
prog.rb:16:in `bind': bind argument must be an instance of B (TypeError)
 from prog.rb:16