package WarnOver;
use strict;
use warnings;

package UNIVERSAL;
use Scalar::Util 'refaddr';
use Carp;
use overload
    q{0+} => sub { 
        carp "numifying reference " . overload::StrVal($_[0]); 
        refaddr $_[0];
    },
    q{""} => sub { 
        carp "stringifying reference " . overload::StrVal($_[0]);
        overload::StrVal($_[0]); 
    },
    fallback => 1;
;
1;

##</code><code>##

use strict;
use warnings;
use lib ".";
use WarnOver;

my $foo = bless {}, "Foo";

$\="\n";
print $foo % 2;
print "$foo";

##</code><code>##

numifying reference Foo=HASH(0x225118) at checkwarn.pl line 10
0
stringifying reference Foo=HASH(0x225118) at checkwarn.pl line 11
Foo=HASH(0x225118)

##</code><code>##

package Foo;
use WarnOver;
$foo = bless {};
$bar = bless {}; 
print "equal" if $foo == $bar; # two warnings!