package MyEmptyTrueVar;
our $singleton;

use overload fallback => 'TRUE',
  '""' => sub { "" }, # Return empty string on stringification
  bool => sub { 1 },  # Return true in boolean context
  '0+' => sub { 1 },  # Return true in numeric context
  cmp  => sub { !ref $_[1] }; # unequal to empty string, or any other string

bless $singleton=\$singleton;

##</code><code>##

say "Single str='$MyEmptyTrueVar::singleton', Num=", (0+$MyEmptyTrueVar::singleton)
   if $MyEmptyTrueVar::singleton &&
   $MyEmptyTrueVar::singleton ne '' &&
   '' ne $MyEmptyTrueVar::singleton;