package Foo;
use overload qw("" stringify fallback 1 + zero);

sub stringify {
  "overload.pm just ruined your day!"
}

sub zero { 0 }

package main;
my $foo1=bless {},'Foo';
my $foo2=bless {},'Foo';

sub same { "'$_[0]' is ".($_[0] eq $_[1] ? "the same as" : "different to" )." '$_[1]'\n" };


print same(0+$foo1,0+$foo2);
print same($foo1,$foo2);
print same("$foo1","$foo2");
print same(overload::StrVal($foo1),overload::StrVal($foo2));

__END__
'0' is the same as '0'
'overload.pm just ruined your day!' is the same as 'overload.pm just ruined your day!'
'overload.pm just ruined your day!' is the same as 'overload.pm just ruined your day!'
'Foo=HASH(0x1acef84)' is different to 'Foo=HASH(0x1acf038)'