sub compact {
    my $ref = shift;
    my $pck;  # Packed information except reference

    # purposefully avoiding dispatch table
    # This keeps us at HoC
    return sub {
        if    ( $_[0] eq 'data' ) { return $ref };
        elsif ( $_[0] eq 'blah' ) { return unpack('A1', $pck) }
        # where each unpack format gets desired data
    };
}

$hash{foo} = compact( [1..10] );
$hash{foo}->( 'data' )[3] = 42;