共用在某個controller底下所有的view，就放在對應這個controller的view目錄下

例如用在views/users/index.html.slim與views/users/show.html.slim的menu，可以放在views/users/_menu.html.slim，在index或show中就能用render "menu"來render menu partial。

共用在不同controller底下的view，就放在views/application的目錄中

例如用在views/users/index.html.slim與views/admins/show.html.slim的menu，可以放在views/application/_menu.html.slim，在users/index或admins/show中就能用render "menu"來render menu partial。

Refs

• Directory for shared partials in Rails - by Dan Croak