Add Where Am I In The Partial Iteration as a rails til

Author: jbranchaud

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_430 TILs and counting..._
+_431 TILs and counting..._
 
 ---
 
@@ -287,6 +287,7 @@ _430 TILs and counting..._
 - [Show Rails Models With Pry](rails/show-rails-models-with-pry.md)
 - [Show Rails Routes With Pry](rails/show-rails-routes-with-pry.md)
 - [Truncate Almost All Tables](rails/truncate-almost-all-tables.md)
+- [Where Am I In The Partial Iteration?](rails/where-am-i-in-the-partial-iteration.md)
 
 ### Ruby
 

rails/where-am-i-in-the-partial-iteration.md

@@ -0,0 +1,22 @@
+# Where Am I In The Partial Iteration?
+
+Let's say I am going to render a collection of posts with a post partial.
+
+```erb
+<%= render collection: @posts, partial: "post" %>
+```
+
+The
+[`ActionView::PartialIteration`](http://api.rubyonrails.org/classes/ActionView/PartialIteration.html)
+module provides a couple handy methods when rendering collections.
+I'll have access in the partial template to `#{template_name}_iteration`
+(e.g. `post_iteration`) which will, in turn, give me access to `#index`,
+`#first?`, and `#last?`.
+
+This is great if I need to do something special with the first or last item
+in the collection or if I'd like to do some sort of numbering based on the
+index of each item.
+
+[source](http://stackoverflow.com/questions/13397848/rails-render-collection-partial-getting-size-of-collection-inside-partial)
+
+h/t Josh Davey