# The "destroy" signal is emitted when a widget is destroyed, either by explicitly calling gtk_widget_destroy() or when the widget is unparented. Top-level GtkWindows are also destroyed when the Close window control button is clicked.
fun on_close(to_call: GtkCallable, user_data: nullable Object)
do
signal_connect("destroy", to_call, user_data)
end
lib/gtk/v3_4/gtk_core.nit:212,2--216,4