sub mock 
{
  my $self = shift; # ref count of the object +1
  # code here 
} # $self goes out of scope, ref count of the object -1


##</code><code>##

sub mock
{
  my $self = shift; # ref count ++
  return sub { $self->{Thing}; };
  # $self is still held by the sub, so it is not freed
}