Your right - forgotten about that.

You still have the problem of overloading tho - what if a subclass overloads "+"?

Unfortunately, there isn't an overload::NumVal to match overload::StrVal (unless I'm missing something somewhere ;-)

You can get around this by blessing the object into another class you know isn't overloaded, get the numeric ID, and then bless the object back into it's original class. For example:

package Foo::Base;
use strict;
use warnings;

sub self {
    my $self = shift;
    my $package = ref($self);
    bless $self, __PACKAGE__;
    my $id = $self+0;
    bless $self, $package;
    return($id);
};


package Foo;
use base qw(Foo::Base);
use strict;
use warnings;

my %foo = ();

sub new {
    my $class = shift;
    bless [], $class;
};

sub foo {
    my $self = shift->self;
    $foo{$self} = @_ if @_;
    $foo{$self};
};

sub DESTROY {
    my $self = shift->self;
    delete $foo{$self};
};
[download]

Mildly evil - but seems to work.