!!some_function 里面的双叹号啥意思

def logged_in? !!current_user end # Accesses the current user from the session. # Future calls avoid the database because nil is not equal to false. def current_user @current_user ||= (login_from_session || login_from_basic_auth || login_from_cookie) unless @current_user == false end

就是两个否

current_user 会返回一个 model 的实例

!current_user 是 false

!false 就是 true 喽