Rust Programming By Example

State mutation

It might not be clear from the previous chapter, but we indirectly used Rc<RefCell<T>> to do state mutation. Indeed, our Playlist type contains a RefCell<Option<String>> and we wrapped our Playlist inside a reference-counted pointer. This was to be able to mutate the state in reaction to events, for instance playing the song when clicking the play button:

let playlist = self.playlist.clone();
let play_image = self.toolbar.play_image.clone();
let cover = self.cover.clone();
let state = self.state.clone();
self.toolbar.play_button.connect_clicked(move |_| {
    if state.lock().unwrap().stopped {
        if playlist.play() {
            set_image_icon(&play_image, PAUSE_ICON);
            set_cover(&cover, &playlist);
        }
    } else { playlist.pause(); set_image_icon(&play_image, ...