Access helper methods outside controllers and views

application_controller.rb

class ApplicationController < ActionController::Base

  # Provide access to helper methods from outside controllers and views,
  # such as in Presenter objects. Rails provides ActionController::Base.helpers,
  # but this does not include any of our application helpers.
  def self.all_helpers
    @all_helpers_proxy ||= begin
      # Start with just the rails helpers. This is the same method used
      # by ActionController::Base.helpers
      proxy = ActionView::Base.new.extend(_helpers)

      # url_for depends on _routes method being defined
      proxy.instance_eval do
        def _routes
          Rails.application.routes
        end
      end
     
      # Import all named path methods
      proxy.extend(Rails.application.routes.named_routes.module)

      # Load all our application helpers to extend
      modules_for_helpers([:all]).each do |mod|
        proxy.extend(mod)
      end

      proxy
    end
  end

end

+1, this is much better than other approaches I found online!