Conditional block-level helper to DRY up views

We're at RailsEdge in Reston and Bruce Williams and Marcel did a little talk on cleaning up views with block helpers, etc.

I wrote a helper of this flavor a while back to DRY up an article rendition issue, so I figured I would throw it up here.

Basically, we have a generic article view but have the need to swap out 'chunks' of the Article in different situations without creating a crazy cartesian product of rendition views.

View now looks like this:

<div class="article_module_head">
  <% unless_partial @article.rendition, 'headline' do %>
    <h2><%= @headline_override || @article.headline %></h2>
  <% end %>
  <% unless_partial @article.rendition, 'subhead' do %>
    <% if @section %>
      <h3><%= @section.title %></h3>
    <% else %>
      <h3><%= @article.subheadline %></h3>
    <% end %>
  <% end %>
...
</div>
...

Helper looks like this:

#
# Allows you to render a block of default code, but instead render a
# partial from a bucket of partials if it's there. Makes it so overriding
# a block of code in a template is as simple as creating a partial -- convention,
# etc.
#
#
# e.g.
#
# @article.rendition #=> 'foo'
#
# <% unless_partial @article.rendition, 'author' do %>
#   <h2 class="article_module_attribution"><%= @article.time_string %></h2>
#   <h2 class="article_module_attribution"><%= @article.author %></h2>
# <% end %>
#
# This block will first check for the _foo partial, then fall back to the block.
#
# Inline version (empty if no partial):
#
# <%= unless_partial @article.rendition, 'aftercopyright' %>
#
#
module ConditionalPartialHelper
  def unless_partial(rendition, partial, &block)
    begin
   output = render :partial => "#{controller.class.controller_path}/#{partial}/#{rendition}"
    if block_given?
        # block given, so they may not be using <%= on the helper call, so you can't just return it.
        concat(output || '', block.binding)
   else
        # no block given, they used <%=
        return output
    end
    rescue ActionView::ActionViewError # no overriding partial
      yield if block_given?
    end
    # contingency for <%= on a with block--the block is doing the concatting
    return ''
  end
end

Hopefully the comment block explains it all.