expose.rb

module Padrino

  # Minimal version of `decent_exposure`[1], in keeping with Padrino's
  # simplicity.
  #
  #   [1] https://github.com/voxdolo/decent_exposure
  #
  # == Usage
  #
  # The first step is to register the plugin with your application:
  #
  #   MyApp.register Padrino::Expose
  #
  # Then use the `expose` method in your controllers to, well,
  # expose the sorts of things you would usually use an instance
  # variable for.
  #
  #   MyApp.controllers :dashboard do
  #     expose(:stats) { Stat.all }
  #     expose(:site) { Site.find(params[:site_id]) }
  #
  #     get :index do
  #       if current_account.site != site
  #         redirect url("/")
  #       else
  #         render :index
  #       end
  #     end
  #   end
  #
  # You can also access the resources from your views!
  #
  #   # views/dashboard/index.slim
  #   - stats.each do |stat|
  #     p == stat.total
  #
  module Expose

    class << self
      def registered(app)
        app.extend ClassMethods
      end

      alias :included :registered
    end

    module ClassMethods

      # Defines a helper method for your controllers and views using the name
      # you provide. Its return value will be the result of the block provided,
      # and will be memoized in an instance variable of the same name.
      #
      # @param name the name for this exposure
      # @param block the block to memoize
      def expose(name, &block)
        ivar = :"@#{name}"

        define_method name do
          if instance_variable_defined?(ivar)
            instance_variable_get(ivar)
          else
            instance_variable_set(ivar, instance_eval(&block))
          end
        end
      end

    end

  end
end