Rails 3: alias_method_chain still used?

Question

I was just reading about Gems/Plugin development for Rails 3 and ran across this post that says that alias_method_chain is no longer used. I can see the method is still ther

Answer 1

In general, a module can never override a method in the class it's included in. This is because module inclusion works just like subclassing. A superclass can't override its subclasses' methods either, nor would you expect it to.

When a module is included in a class, the module is inserted just after the class in the class's ancestor chain. Calling super from the class will call the module's implementation.

class Something
  module PreExtension; end
  module PostExtension; end

  include PreExtension
  include PostExtension
end

Something.ancestors # => [Something, Something::PostExtension, Something::PreExtension, Object, Kernel]

Whenever a method is called on a Something, Ruby looks through this list in order and calls the first implementation it finds. If the implementation calls super, it keeps looking and finds the next one.

This means that modules included later take precedence over modules included earlier, and can call super to get the earlier modules' implementations. This is because included modules are inserted in the ancestor chain directly after the class. This is how the routing code edgerunner mentioned works. That code puts everything in modules, like so:

class SomethingNew
  module Base
    def my_method
      puts "(A)"
    end
  end

  module Extension
    def my_method
      puts "(B)"
      super
    end
  end

  include Base
  include Extension
end

SomethingNew.new.my_method
# Output:
# >> (B)
# >> (A)

SomethingNew.ancestors # => [SomethingNew, SomethingNew::Extension, SomethingNew::Base, Object, Kernel]

This is why alias_method_chain existed in the first place. If putting the base code in a module is not an option, I'm not sure how to accomplish the equivalent of alias_method_chain.