overload.pl

use strict;
use warnings;
use utf8;

package Foo {
    use overload (
        bool  => sub { warn 'this is bool' },
        q{""} => sub { warn 'this is stringify' },
    );

    sub new { bless {}, shift }
}

my $foo = Foo->new;

warn 'hi'  if $foo;
warn 'hoi' if defined $foo;

my $bar = $foo;
my $baz = $foo . 'fooray';

15:30 > perl overload.pl
this is bool at overload.pl line 7.
hi at overload.pl line 16.
hoi at overload.pl line 17.
this is stringify at overload.pl line 8.