The code executes different method according to the environment, in Rails. In this way, you can show message only in development environment.
In Ruby, we can use
&&. And also
|| we can use. I researched about their difference.
I wrote the way to build structured layout in Rails.
You can use it when you want to use the same frame according to the page URLs. For example, to show control bar in admin pages.
These days, I explain the difference between class and instance as follows.