Problems with custom statuses | WordPress.org

Hello, I wanted to add a custom status to event posts, and I saw this article:
https://theeventscalendar.com/knowledgebase/adding-a-custom-event-status

 I have put the code in my functions.php, like many other snippets, but it gives me this error:

PHP Parse error: syntax error, unexpected ‘public’ (T_PUBLIC)

Furthermore, I have seen that the article code and the video code do not match…