my $closure = sub {
        my $field = shift;
        $self->{$field}->{'ACCESS'} eq 'private' 
            and caller(0) eq __PACKAGE__
            || confess "$field is private";
        $self->{$field}->{'ACCESS'} eq 'protected' 
            and caller(0)->isa(__PACKAGE__)
            || confess "$field is protected";
        if ( @_ ) { $self->{$field}->{'VALUE'} = shift; }
        return $self->{$field}->{'VALUE'};
    };