# dualvar.pl
package DualVar;

use strict;
use warnings;

use overload
'bool' => \&overload_true,
'.'    => \&overload_concat;

sub overload_true {
  # Return 1 if either $obj->[0] or $obj->[1]
  # are true. Else return 0.

  my $obj = shift;
  if($obj->[0] || $obj->[1]) { return 1 }
  return 0;
}

sub overload_concat {
  my ($obj, $other, $reversed) = (shift, shift, shift);
  if($reversed) { return $other . $obj->[1] }
  return $obj->[1] . $other;
}

# The above procedures would normally be put into
# a module, which would be loaded as needed.
# The code below relies on the above procedures.
# Here we see that $x is True, and also that $y
# remains unchanged when $x is concatenated onto it.

my $x = [1, ""];
my $y = "hello";
my ($r1, $r2);

bless $x, 'DualVar';

if($x) {
  $r1 = $x . $y;
  $r2 = $y . $x;
}

print "# ok 1\n" if $r1 eq $y;
print "# ok 2\n" if $r2 eq $y;

# Outputs:
# ok 1
# ok 2