title: How do I include Responder in ActionController::Metal in Rails 3?
body: <p>I'm working a Rails 3 controller that has a very specific, limited purpose, and all I need is for it to respond_to :json. </p>
  
  <p>This screencast says my controller can inherit from ActionController::Metal, and then just include the functionality I need to make things faster:
  <a href="http://rubyonrails.org/screencasts/rails3/action-controller" rel="nofollow noreferrer">http://rubyonrails.org/screencasts/rails3/action-controller</a></p>
  
  <p>When my controller looks like this:</p>
  
  <pre><code>class FoldersController &lt; ActionController::Metal
    respond_to :json
    def all
      respond_with Folder.all
    end
  end
  </code></pre>
  
  <p>I get the error:</p>
  
  <pre><code>undefined method `respond_to' for FoldersController:Class
  </code></pre>
  
  <p>I've tried including Responder, ActionController::Responder, ActionController::Metal::Responder, but none of them work. What do I include to get this responder functionality?</p>