has 'dir'  => ( is => 'ro', isa => 'IO::Dir', required => 1 );

    around BUILDARGS => sub {
        $_ = shift for my ($orig, $class);
        my %args = @_;

        die 'required dir missing' unless exists $args{dir};

        return $class->$orig(dir => 'IO::Dir'->new($args{dir}))
    }