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

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

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+# 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.