I'm sorry: I think I was very unclear in the original question, and simplified away the wrong bits. It's the package name of the factory that I want to capture in a method injected into the Drone class, so that the Drone (no idea why I called it that) can call instance() on the right factory class.

The answer turns out to be very simple, and much the same as your neat constructions:

sub post_require { 
    my ($self, $class) = shift;
    my $factory_class=ref $self;
    no strict 'refs';
    *{"$class::factory"} = sub { return $factory_class->instance; };
}
[download]

but it does look like I can't do it without creating some kind of closure, which I was hoping to avoid...

Thanks for your help.