{
    my $c = wrapper->instance;
    my $d = wrapper->instance;
    die "Mismatch" if $c != $d;
}   # wrapper->instance expires
{
    my $e = wrapper->instance;
    {
        my $f = wrapper->instance;
        die "Mismatch" if $e != $f;
    }
}   # wrapper->instance expires

package wrapper;
BEGIN { our @ISA = ('Class::WeakSingleton') }
sub ::DEBUG { 1 }
my $count = 0;
sub _new_instance {
    print "_new_instance()\n" if ::DEBUG;
    bless { (++$count) x 2 }, shift;
}

package Class::WeakSingleton;
use Scalar::Util ();

sub instance {
    my $class = shift;

    # get a reference to the _instance variable in the $class package
    no strict 'refs';
    my $instance = "${class}::_instance";

    return $$instance if defined $$instance;

    my $new_instance = $class->_new_instance(@_);
    $$instance = $new_instance;

    Scalar::Util::weaken( $$instance );

    return $new_instance;
}