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git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

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diff --git a/actionpack/lib/action_view/partials.rb b/actionpack/lib/action_view/partials.rb
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+module ActionView
+  # There's also a convenience method for rendering sub templates within the current controller that depends on a single object 
+  # (we call this kind of sub templates for partials). It relies on the fact that partials should follow the naming convention of being 
+  # prefixed with an underscore -- as to separate them from regular templates that could be rendered on their own. In the template for 
+  # Advertiser#buy, we could have:
+  #
+  #   <% for ad in @advertisements %>
+  #     <%= render_partial "ad", ad %>
+  #   <% end %>
+  #
+  # This would render "advertiser/_ad.rhtml" and pass the local variable +ad+ to the template for display.
+  #
+  # == Rendering a collection of partials
+  #
+  # The example of partial use describes a familar pattern where a template needs to iterate over an array and render a sub
+  # template for each of the elements. This pattern has been implemented as a single method that accepts an array and renders
+  # a partial by the same name as the elements contained within. So the three-lined example in "Using partials" can be rewritten
+  # with a single line:
+  #
+  #   <%= render_collection_of_partials "ad", @advertisements %>
+  #
+  # This will render "advertiser/_ad.rhtml" and pass the local variable +ad+ to the template for display. An iteration counter
+  # will automatically be made available to the template with a name of the form +partial_name_counter+. In the case of the 
+  # example above, the template would be fed +ad_counter+.
+  # 
+  # == Rendering shared partials
+  #
+  # Two controllers can share a set of partials and render them like this:
+  #
+  #   <%= render_partial "advertisement/ad", ad %>
+  #
+  # This will render the partial "advertisement/_ad.rhtml" regardless of which controller this is being called from.
+  module Partials
+    def render_partial(partial_path, object = nil, local_assigns = {})
+      path, partial_name = partial_pieces(partial_path)
+      object ||= controller.instance_variable_get("@#{partial_name}")
+      render("#{path}/_#{partial_name}", { partial_name => object }.merge(local_assigns))
+    end
+
+    def render_collection_of_partials(partial_name, collection, partial_spacer_template = nil)
+      collection_of_partials = Array.new
+      collection.each_with_index do |element, counter|
+        collection_of_partials.push(render_partial(partial_name, element, "#{partial_name.split("/").last}_counter" => counter))
+      end
+
+      return nil if collection_of_partials.empty?
+      if partial_spacer_template
+        spacer_path, spacer_name = partial_pieces(partial_spacer_template)
+        collection_of_partials.join(render("#{spacer_path}/_#{spacer_name}"))
+      else
+        collection_of_partials
+      end
+    end
+    
+    private
+      def partial_pieces(partial_path)
+        if partial_path.include?('/')
+          return File.dirname(partial_path), File.basename(partial_path)
+        else
+          return controller.send(:controller_name), partial_path
+        end
+      end
+  end
+end