refine_class_method.rb

class Foo
  def self.foo
    "foo"
  end
  def foo
    "ifoo"
  end
end

module Interceptor
  refine Class do
    def Foo.foo
      "bar"
    end
  end
  refine Foo do
    def foo
      "ibar"
    end
  end
end

using Interceptor

p Foo.foo    #=> "bar"
p Foo.new.foo #=> "ibar"