use Math::GMP;
$orig = Math::GMP->new(5);
$copy = $orig;
$copy += 4; # $copy is 9
            # $orig is 4

##</code><code>##

use Math::GMP;
$orig = Math::GMP->new(5);
$copy = $orig;
$copy->add_ui_gmp(4); # $copy is 9
                      # $orig is 9