We previously saw how to communicate with the same widget. To send a message to the same widget from an event handler in the view, we simply need to specify the message to be sent on the right side of =>, like in the following example:
gtk::ToolButton { icon_widget: &new_icon("gtk-quit"), clicked => Quit, }
Here, the Quit message is sent to the same widget (that is, App) when the user clicks this tool button. But this is syntax sugar for a call to the emit() method on the stream of events of a relm widget.