use strict;
use warnings;
use Math::GMP;

my $orig = Math::GMP->new(2);
my $copy = $orig;

# At this point $copy and $orig refer to
# one and the same Math::GMP object.

$copy += 5;

# At this point, $copy refers to a newly
# created Math::GMP object that holds a
# value of 7; $orig still refers to the
# original object, holding a value of 2.

print "$orig\n"; # prints 2
print "$copy\n"; # prints 7

##</code><code>##

use overload
  ... ,
  '=' => \&overload_copy,
  ... ;