my $code;
{
    my @arr = (9) x 1000_000;
    $code = sub { @arr };
}
# here @arr got out of the scope but is not freed as 
# there's a ref from inside $code closure
# which enables $code do things with the array when called
undef $code;
# only now that million of nines has gone away
# it always existed in exactly one copy