Proffer

A module to stop Action Controller from copying every instance variable available to an action to the view by default. Instead, Proffer provides a way to explicitly expose values as local variables within views.

Rationale

By default, Action Controller will make any instance variables present during an action available to its views (including partials). This effectively makes them global variables and can obscure their origin when maintaining views. Partials that exploit this behaviour can be particularly difficult to maintain as they may inherit state from their caller implicitly.

We want to see if removing this default behaviour changes the way views are written. By forcing explicit declaration of dependencies, will better, more encapsulated design result?

Usage

Add the following to your Gemfile:

gem 'proffer'

Include the Proffer module into any controllers you wish (include into ApplicationController to enforce this behaviour throughout your application):

class PostsController < ApplicationController
  include Proffer

  # This will make a new Post object available as post in the view but
  # @heading will be nil.
  def new
    @heading = "New Post"
    proffer :post => Post.new
  end
end

Any proffered values will then be available to your views by their key:

<%= form_for(post) do |f| %>
  ...
<% end %>

You can test your use of Proffer by inspecting the proffered method on your controllers instead of using assigns like so:

describe FooController do
  describe "GET index" do
    it "only proffers the title" do
      get :index
      controller.proffered.should == { :title => "Title" }
    end
  end
end

Note that if you set @title in a Proffer-enabled action, assigns(:title) will be nil.

Compatibility

As we rely on ActionController#view_assigns, this will only work with versions of Rails 3.0 or later. It is currently tested against Rails 3.2.

Disclaimer

We have not yet tried this in production so proceed with caution. This gem overrides ActionController#view_assigns and extends ActionController#render, so it may be incompatible with other gems that override these methods.

License

See LICENSE.txt