DestroyDetector class, helps us to detect when a variable is garbage-collected.

Piece1-DestroyDetector.pm

package DestroyDetector;
sub new {
  my ($pkg, $val) = @_;
  my $self = {value=>$val};
  return bless $self, $pkg;
}

sub value {
  my ($self) = @_;
  return $self->{value};
}

sub announce {
  my ($self, $msg) = @_;
  $msg //= q{};
  say "Announcing DestroyDetector \"$msg\" value: ".$self->value;
}

sub DESTROY {
  my ($self) = @_;
  say "Destroying DestroyDetector value: ".$self->value;
  return;
}