what is the best practice strategy in kotlin/android to save an array and use it after?

after what?

my case is I have setData(ArrayFromRetrofit) and need to have a new and old instance because I am using a DiffUtil that compare old and new array retrieved from Retrofit to compare them and detect changes. So I would like to retain the state of the first array, because I lose the scope/status when I do a retrofit call

I guess it depends on what you're worried about losing state. If the fragment never dies but you're just making two network calls, you can cache it in the fragment. A companion object sticks around as long as the application does (for the most part). If you want to persist across sessions you'd need shared prefs or a DB.

so I guess a companion object is the most idiomatic way to go

Of course! I don't wanna be a heckler, but we try our best to keep this chat kotlin specific, so please check out Android United. I'm also always happy to chat about Android via DM but I'm not always on line. 🙂

really kind of you for the community