Ruby: modules and super?

Question

I don't understand why this works.

module Base   attr_reader :first   def setup     @first = 1   end end  module Addon   attr_reader :second   def setup     #super     @second = 2   end end  class Test   include Base   include Addon    def initialize(num)     @num = num     setup   end end  a = Test.new(1) p a.first p a.second 

Basically I have a "base" module, which sets up some stuff. I also have an addon module, which sets up some more stuff if some class wants to include it.

Now when I test it, if I don't have that super call, I get

nil 2 

When I do have the super call, I get

1 2 

What does super actually do here? It's calling the setup method from the Base module, even when Base and Addon are not related.

This is the first time I've used super in the context of modules. Previously I've always used super calls with classes and thought it was just going up the inheritance tree to find a parent with the same method.

Is including multiple modules also setting up some sort of inheritance tree?

EDIT: for context, the Addon module will never be included without the Base module, and the Base module will always be included before any additional Addon modules.

Answer 1

Yes, when you include modules, they are injected into inheritance chain

Test.ancestors # => [Test, Addon, Base, Object, Kernel, BasicObject] 

Addon module, when included, redefines existing setup method from Base. If you want Base's version be called, use super.