use base 'Class::Accessor::Fast';
HelloGtk->mk_accessors(qw(button));

:!perl /home/jakob/gtk
Base class package "Class::Accessor::Fast" is empty.
    (Perhaps you need to 'use' the module which defines that package first.)
 at /home/jakob/gtk line 16
BEGIN failed--compilation aborted at /home/jakob/gtk line 16.

Shell beendet 2   

Base class package "Foo::Bar::XYZ" is empty.
    (Perhaps you need to 'use' the module which defines that package first,
    or make that module available in @INC (@INC contains: ...