How are require, require_dependency and constants reloading related in Rails?

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How are require and require_dependency different?
How can require_dependency automatically reload classes in development but require can't ?

I digged into Rails' ActiveSupport::Dependencies and dispatcher.rb code. What I saw in require_dependency's code is it basically adds the constants to an autoloaded_constants array. But it gets cleared in clear_application inside dispatcher after each request.

Can someone give a clear explanation or point me to some resources which will help?

require ruby-on-rails
2 Answers

require_dependency is useful in an engine when you want to re-open a class which is not defined in your engine (for example in another engine or Rails app) and have it reloaded. In which case something like this works:

# app/controllers/my_engine/documents_controller.rb
require_dependency MyEngine::Engine.root.join('app', 'controllers', 'my_engine', 'documents_controller').to_s

module MyEngine
  class DocumentsController
    def show
      render :text => 'different'
    end
  end
end
user_222370
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