Add Use .ruby Extension For Template File as a Rails TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1700 TILs and counting..._
+_1701 TILs and counting..._
 
 See some of the other learning resources I work on:
 
@@ -1196,6 +1196,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Update Column Versus Update Attribute](rails/update-column-versus-update-attribute.md)
 - [Upgrading Your Manifest For Sprocket's 4](rails/upgrading-your-manifest-for-sprockets-4.md)
 - [Use IRB And Ruby Flags With Rails Console](rails/use-irb-and-ruby-flags-with-rails-console.md)
+- [Use .ruby Extension For Template File](rails/use-ruby-extension-for-template-file.md)
 - [Useful ActiveSupport Constants For Durations](rails/useful-active-support-constants-for-durations.md)
 - [Validate Column Data With Check Constraints](rails/validate-column-data-with-check-constraints.md)
 - [Verify And Read A Signed Cookie Value](rails/verify-and-read-a-signed-cookie-value.md)

rails/use-ruby-extension-for-template-file.md

@@ -0,0 +1,42 @@
+# Use .ruby Extension For Template File
+
+An interesting feature of Rails that I can't seem to find documented anywhere is
+that you can write a template file with plain Ruby by using the `.ruby`
+extension. For instance, you might want to render some JSON from a template.
+Instead of using `jbuilder` or `erb`, you can have a `show.json.ruby` file. This
+is also popular with Turbo Stream files -- e.g. `update.turbo_stream.ruby`.
+
+How this works is that the entire file is evaluated as if it were a `.rb` file.
+Then the return value of the final statement is what is returned and rendered by
+Rails.
+
+```ruby
+author_byline = @book.authors.map(&:name).to_sentence
+
+data = {
+  id: @book.id,
+  title: @book.title,
+  author: author_byline,
+  status: @book.published_at > Time.current ? 'Coming Soon' : 'Published',
+  publication_year: @book.published_at.year
+}
+
+data.to_json
+```
+
+That final line converts the hash of data that we've built up into a JSON string
+that can then be rendered by the controller action that corresponds to this view
+template.
+
+Similarly, you can have a Turbo Stream template `show.turbo_stream.ruby` that
+looks something like this:
+
+```ruby
+[
+  turbo_stream.prepend("posts", @post),
+  turbo_stream.update("form", partial: "form", locals: { post: Post.new })
+].join
+```
+
+This template file is made up of a single statement which is an array of turbo
+stream results that get joined together.