+ # The application is completely hidden from the user
+ #
+ # It may then be destroyed or go back to a paused state with `on_restart`.
+ #
+ # Triggers are platform specific:
+ # * Android: `Activity.onStop`
+ # * iOS: `UIApplicationDelegate applicationDidEnterBackground`
+ fun on_stop do end
+
+ # The application returns to a visible state from a previous `on_stop`
+ #
+ # Triggers are platform specific:
+ # * Android: `Activity.onRestart`
+ # * iOS: `UIApplicationDelegate applicationWillEnterForeground`
+ fun on_restart do end
+
+ # The application may be destroyed soon, save its state for a future `on_restore_state`
+ #
+ # Triggers are platform specific:
+ # * Android: `Activity.onSaveInstanceState`
+ # * iOS: `UIApplicationDelegate applicationDidEnterBackground`
+ fun on_save_state do end
+
+ # The application is launching, restore its state from a previous `on_save_state`
+ #
+ # Triggers are platform specific:
+ # * Android: `Activity.onCreate`, _not_ `Activity.onRestoreInstanceState`
+ # as it is trigged only if there is a previous Android specific save state.
+ # * iOS: `UIApplicationDelegate applicationDidEnterBackground`
+ fun on_restore_state do end