Nestive, A Nested Inheritable Layouts Plugin for Rails

Note: This is ridiculously alpha proof-of-concept seeking feedback. Things will change.

Nestive adds powerful layout and view helpers to your Rails app. It's similar to the nested layout technique already documented in the Rails guides and found in many other nested layout plugins (a technique using content_for and rendering the parent layout at the end of the child layout). There's a bunch of problems with this technique, including:

you can only append content to the content buffer with content_for (you can't prepend to content, you can't replace it)
when combined with this nested layout technique, content_for actually prepends new content to the buffer, because each parent layout is rendered after it's child

Nestive is better because it addresses these problems.

Just five methods (so far) – `area`, `extend`, `append`, `prepend`, `replace`.

Declaring an area of content in your parent layout with `area`:

The area helper is a lot like Rails' own <%= yield :foo %>, and is used in layouts to define and render a chunk of content in your layout:

<%= area :sidebar %>

Unlike yield, area will allow your parent layouts to add content to the area at the same time using either a String or a block:

<%= area :sidebar, "Some Content Here" %>

<%= area :sidebar do %>
  Some Content Here
<% end %>

It's important to note that this isn't default content, it is the content (unless a child changes it).

Extending a layout in a child layout (or view):

Any layout (or view) can declare that it wants to inherit from and extend a parent layout, in this case we're extending app/views/layouts/application.html.erb:

<%= extends :application do %>
   ...
<% end %>

You can nest many levels deep:

# app/views/posts/index.html.erb
<%= extends :blog do %>
   ...
<% end %>

# app/views/layouts/blog.html.erb
<%= extends :public do %>
   ...
<% end %>

# app/views/layouts/public.html.erb
<%= extends :application do %>
   ...
<% end %>

Appending content to an area:

The implementation details are quite different, but the append helper works much like Rails' built-in content_for. It will work with either a String or block, adding the new content onto the end of any content previously provided by parent layouts:

<%= extends :application do %>
  <%= append :sidebar, "More content." %>
  <%= append :sidebar do %>
    More content.
  <% end %>
<% end %>

Prepending content to an area:

Exactly what you think it is. The reverse of append (duh), adding the new content at the start of any content previously provided by parent layouts:

<%= extends :application do %>
  <%= prepend :sidebar, "Content." %>
  <%= prepend :sidebar do %>
    Content.
  <% end %>
<% end %>

Replacing content

You can also replace any content provided by parent layouts:

<%= extends :application do %>
  <%= replace :sidebar, "New content." %>
  <%= replace :sidebar do %>
    New content.
  <% end %>
<% end %>

The token blog example

Set-up a global layout defining some content areas. Note that there is no <% yield %> here.

# app/views/layouts/application.html.erb
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title><%= area :title %> JustinFrench.com</title>
  <meta name="description" content="<%= area :description, "This is my website." %>">
  <meta name="keywords" content="<%= area :keywords, "justin, french, ruby, design" %>">
</head>
<body>
  <div id="wrapper">
    <div id="content">
      <%= area :content do %>
        <p>Default content goes here.</p>
      <% end %>
    </div>
    <div id="sidebar">
      <%= area :sidebar do %>
        <h2>About Me</h2>
        <p>...</p>
      <% end %>
    </div>
  </div>
</body>
</html>

Next, we set-up a blog layout that extends application, replacing, appending & prepending content to the areas we defined earlier.

# app/views/layouts/blog.html.erb
<%= extends :application do %>
  <% replace :title, "My Blog – " %>
  <% replace :description, "Justin French blogs here on Ruby, Rails, Design, Formtastic, etc" %>
  <% prepend :keywords, "blog, weblog, design links, ruby links, formtastic release notes, " %>
<% end %>

Now our blog index view can extend blog and fill in the areas with content specific to the index action.

# app/views/posts/index.html.erb
<%= extends :blog do %>
  <% replace :content do %>
    <h1>My Blog</h1>
    <% render @articles %>
  <% end %>

  <% append :content do %>
    <h2>Blog Roll</h2>
    <% render @links %>
  <% end %>
<% end %>

We also need to instruct the PostsController not to wrap the view in a layout of it's own (default Rails behavior), which can be done on an individual action:

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def index
    render :layout => nil
  end
end

Or for an entire controller:

# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  layout nil
end

Or for every controller:

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  layout nil
end

We'll find a way to make this easier or a bit more obvious in a future version.

Installation

add gem 'nestive', '~> 0.1' to your gemfile
run bundle
add layout nil to ApplicationController or the specific controllers you want to use Nestive on (see above)

TODO

Figure out how to test it
Actually use it in an app
You know, everything!

Compatibility

Only testing it with Rails 3.1 RCs right now, but it should work with Rails 2 & 3. The dependency is set to ~> 3.0 right now, will change to 2.x when someone can test it works.

Nestive doesn't monkey patch or fiddle with any default behaviors in Rails. Use it when you want to, don't when you don't.

You can help with...

feedback
reporting issues
fixing issues with pull requests
performance testing