Add Why Redirect And Return In Controllers as a Rails TIL

Author: jbranchaud

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).
 
-_1260 TILs and counting..._
+_1261 TILs and counting..._
 
 ---
 
@@ -857,6 +857,7 @@ _1260 TILs and counting..._
 - [Use IRB And Ruby Flags With Rails Console](rails/use-irb-and-ruby-flags-with-rails-console.md)
 - [Verify And Read A Signed Cookie Value](rails/verify-and-read-a-signed-cookie-value.md)
 - [Where Am I In The Partial Iteration?](rails/where-am-i-in-the-partial-iteration.md)
+- [Why Redirect And Return In Controllers](rails/why-redirect-and-return-in-controllers.md)
 - [Wipe Out All Precompiled Assets](rails/wipe-out-all-precompiled-assets.md)
 - [Write Reversible Migration To Set Default](rails/write-reversible-migration-to-set-default.md)
 - [Write Safer Where Clauses With Placeholders](rails/write-safer-where-clauses-with-placeholders.md)

rails/why-redirect-and-return-in-controllers.md

@@ -0,0 +1,38 @@
+# Why Redirect And Return In Controllers
+
+A fairly common idiom in Rails controller actions is a `redirect_to` followed
+by an `and return`.
+
+```ruby
+def show
+  redirect_to sign_in_path and return if current_user.blank?
+
+  book = Book.find(params[:id])
+
+  render book
+end
+```
+
+Because a `render` comes later in the controller action, we need to _early
+return_ after the redirect to avoid multiple render/redirect warnings.
+
+It is important to use `and` here instead of `&&` because of logical operator
+precedence.
+
+If we used `&&` instead:
+
+```ruby
+  redirect_to sign_in_path && return if current_user.blank?
+```
+
+The `redirect_to` would get `nil` (the result of `sign_in_path && nil`). If we
+did want to use `&&`, we'd need to be diligent with method call parentheses.
+
+```ruby
+  redirect_to(sign_in_path) && return if current_user.blank?
+```
+
+In this case, `redirect_to` would actually get called with a path string and
+the `return` would be called after that.
+
+[source](https://stackoverflow.com/a/37211314/535590)