Add Why Redirect And Return In Controllers as a Rails TIL

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

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+# 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)