Perl and Gtk2 menu

今天主要學到了選單(menu)的寫法，不過它使用的資料型態我看不太懂，似乎跟物件有關，看起來很奇怪。

以下是有關menu部份的code

use Gtk2::SimpleMenu;
my $menu_tree = [
    _File => {
        item_type => "<Branch>",
        children => [
            _Quit => {
                callback => sub { Gtk2->main_quit;},
                callback_action => 0,
                accelerator => "<ctrl>Q",
                },
            ]
        }
    ];
my $menu = Gtk2::SimpleMenu->new (
    menu_tree => $menu_tree,
    default_callback => sub { print "hello";},
    user_data => "user_data"
    );
$vbox->pack_start ($menu->{widget},0 ,0 ,0);