perl -E '
  $o = bless \$o, 0;
  *{"0::barf"} = sub {say "woof $_[1]"};
  $foo = 0;
  $foo->barf("warf");
  say $o;
  $o->barf("chrrr, wuff!");
  0->barf("what?")'
woof warf
0=REF(0x1267880)
woof chrrr, wuff!
woof what?