How to undefine class in Ruby?

Question

Undefining a method in Ruby is pretty simple, I can just use undef METHOD_NAME.

Is there anything similar for a class? I am on MRI 1.9.2.

I have to undefine an ActiveRecord Model, run two lines of code, and restore the model back to its original form.

The problem is, I have an model Contact and I am using a company's API and it happens that they have some class called Contact, and changing my model name would be lot of work for me.

What can I do in this situation?

score 108 · Accepted Answer · edited Jan 09 '20 at 10:13

108

class Foo; end
# => nil
Object.constants.include?(:Foo)
# => true
Object.send(:remove_const, :Foo)
# => Foo
Object.constants.include?(:Foo)
# => false
Foo
# NameError: uninitialized constant Foo

EDIT Just noticed your edit, removing the constant is probably not the best way to achieve what you're looking for. Why not just move one of the Contact classes into a separate namespace.

EDIT2 You could also rename your class temporarily like this:

class Foo
  def bar
    'here'
  end
end

TemporaryFoo = Foo
Object.send(:remove_const, :Foo)
# do some stuff
Foo = TemporaryFoo
Foo.new.bar #=> "here"

Again, the trouble with this is that you'll still have the newer Contact class so you'll have to remove that again. I would really recommend name-spacing your classes instead. This will also help you avoid any loading issues

edited Jan 09 '20 at 10:13

Sebastián Palma

32,692
6
40
59

answered Jul 16 '12 at 11:47

Lee Jarvis

16,031
4
38
40

2

No, you would probably need to remove the `contact.rb` file from `$LOADED_FEATURES` and then reload it but that may have some side effects. I didn't notice your edit when I first wrote my answer so I've updated it. That said, you may be able to temporarily rename it. – Lee Jarvis Jul 16 '12 at 11:50
how to temporary rename? I'll rename, run code and rename it back. that sounds good? – Bhushan Lodha Jul 16 '12 at 11:53
Check my update, again I don't recommend this approach but that's how it could be done – Lee Jarvis Jul 16 '12 at 11:54

ZimbiX · Answer 2 · 2016-02-25T15:16:59.510

In a similar situation - mocking a class used internally by another class I'm trying to test - I found this to be a workable solution:

describe TilesAuth::Communicator do
  class FakeTCPSocket
    def initialize(*_); end
    def puts(*_); end
  end

  context "when the response is SUCCESS" do
    before do
      class TilesAuth::Communicator::TCPSocket < FakeTCPSocket
        def gets; 'SUCCESS'; end
      end
    end
    after { TilesAuth::Communicator.send :remove_const, :TCPSocket }

    it "returns success" do
      communicator = TilesAuth::Communicator.new host: nil, port: nil, timeout: 0.2
      response = communicator.call({})
      expect(response["success"]).to eq(true)
      expect(response).not_to have_key("error")
      expect(response).not_to have_key("invalid_response")
    end
  end
end

I would have thought there would be a better way to do this - i.e. I couldn't see a way to pass in the desired return value for reuse - but this seems good enough for now. I'm new to mocking/factories, and I'd love to hear about any alternative methods.

Edit:

Ok, so not so similar after all.

I found a better way using RSpec mock, thanks to an excellent explanation in the RSpec Google Group:

context "with socket response mocked" do
  let(:response) do
    tcp_socket_object = instance_double("TCPSocket", puts: nil, gets: socket_response)
    class_double("TCPSocket", new: tcp_socket_object).as_stubbed_const
    communicator = TilesAuth::Communicator.new host: nil, port: nil, timeout: 0.2
    communicator.call({})
  end

  context "as invalid JSON" do
    let(:socket_response) { 'test invalid json' }

    it "returns an error response including the invalid socket response" do
      expect(response["success"]).to eq(false)
      expect(response).to have_key("error")
      expect(response["invalid_response"]).to eq(socket_response)
    end
  end

  context "as SUCCESS" do
    let(:socket_response) { 'SUCCESS' }

    it "returns success" do
      expect(response["success"]).to eq(true)
      expect(response).not_to have_key("error")
      expect(response).not_to have_key("invalid_response")
    end
  end
end

How to undefine class in Ruby?

2 Answers2

Linked