Question

I’m attempting to use both Perl’s autoboxing functionality and operator overloading functionality, and they don’t seem to be working in tandem.

Is it possible I am missing some nuance of how to use overload properly, or is this some sort of odd deviant behavior?

Sample Code:

#!/usr/bin/perl
use strict;
use warnings;

package overload_me;
use overload('+' => "overloaded_add");
sub overloaded_add{
    my ($me, $him) = @_;
    $me+$him+1;
}

use autobox NUMBER => 'overload_me';
my $autoboxing_test = 4->overloaded_add(5);
my $overloading_test = 4 + 5;
print "Autoboxing test: 4+5=$autoboxing_test 
Overloading test: 4+5=$overloading_test\n";

Test output:

Autoboxing test: 4+5=10 Overloading test: 4+5=9

Answer 1

Autoboxing doesn’t cause 4 to be an instance of overload_me. It causes method calls with 4 on their left hand side to call methods in overload_me. This is a subtle distinction but an important one, because it means that overload just doesn’t apply at all. 4 isn’t an object and doesn’t belong to any class. It’s still just 4 and when you calculate 4 + 5 it’s still just 4 + 5.

From the autobox docs:

The autoboxing is transparent: boxed values are not blessed into their (user-defined) implementation class (unless the method elects to bestow such a blessing) – they simply use its methods as though they are.