package MyPackage;
  sub new {
      my $self = $_[0];
      bless { foo => $_[1] }, ref($self) || $self;
  }

  package main;
  my $a = MyPackage::->new(1);

##</code><code>##

  package main;
  my $b = $a;

##</code><code>##

  my $c = $a + $b;

##</code><code>##

  package MyPackage;
  use overload q/+/ => \&add;

  sub add {
      $_[0]->new( $_[0]->{foo} + (ref($_[1]) ? $_[1]->{foo} : $_[1]) )
  }

##</code><code>##

  package main;
  my $c = $a + $b;

##</code><code>##

  $b++;

##</code><code>##

  package MyPackage;
  use overload q/++/ => sub { $_[0]->{foo}*=2; shift };

  package main;
  $d = $c;
  $d++;

##</code><code>##

  package MyPackage;
  use overload q/=/ => sub { $_[0]->new($_[0]->{foo}) };

##</code><code>##

  package main;
  $d = $c;

##</code><code>##

  $d++;