Idea for good defaults that are easy to opt-out of with John Leighton's Focus Controllers

gistfile1.rb

class PostsController
  # You could believe we have a FcousedAction module that gives us 
  # good defaults. It exposes things like +action+ for defining
  # normal RESTful actions.
  include FocusedActions
  
  # Example 1:
  # The default behaviour is enough.
  action :index
  action :create
  
  # Example 2:
  # The default behaviour is almost enough. We have our own way of finding
  # posts and opt-out of the default.
  #
  # Under the hood, +action+ uses this class and works out the name from
  # the controller. Or something like that.
  class Show < FocusedActions::Action::Show
    exposes :post, { Post.find_by_slug(params[:slug]) }
  end
  
  # Example 3:
  # We need to do something very different. Opt-out of the default
  # behaviour entirely.
  #
  # Under the hood, FocusedActions::Action does something like this
  # for us.
  class Destroy
    include FocusedController::Mixin

    attr_writer :post
    
    def run
      if post.comments.any?
        render :destroy, :alert => t('posts.destroy.failure')
      else
        post.destroy
        redirect_to :index
      end
    end
    
    def post
      @post ||= Post.find_by_slug(params[:slug])
    end
    helper_method :post
  end
end

The idea is that the highest level is simply the composition of smaller components which you can peel back the further you need to customise. Each action is isolated and can easily be swapped out for another one.