my $sq = TestSequence -> new();
$sq -> define( 'BB', undef() );
for (my $i = 0; $i < 1000000; $i++ ) {
    my %hash;
    # fill the hash, then later...
    $sq -> { BB }[ $i ] = \%hash;
}
# do something useful with $sq, then later...
$sq -> prune( 'BB' );