package My;
use fields qw(bar);
sub new {
    return fields::new(shift)
}
1;

##</code><code>##

package Foo;
use fields qw(foo);
sub new {
    return fields::new(shift)
}
1;

##</code><code>##

#!/usr/bin/perl

use My;
use Foo;
use strict;

my $bar = [];
print "\$bar = $bar\n";
my My $my = $bar;

$my->{bar} = 'quux';
print "\$my = $my\n";
print "my bar field: $my->{bar}\n";
print "bar: (",@$bar,")\n";

my $foo = Foo->new();
$foo->{foo} = 'is foo';
print "(1)foo: $foo, foo field = ".$foo->{foo},"\n";

my My $bar = $foo;
$bar->{bar} = 'is bar';

print "(2) bar: $bar, bar field = ".$bar->{bar},"\n";
print "(3) foo: $foo, foo field = ".$foo->{foo},"\n";
print "(4) foo: $foo, foo field = ".$foo->{bar},"\n";
__END__
$bar = ARRAY(0x827ac28)
$my = ARRAY(0x827ac28)
my bar field: quux
bar: (quux)
(1) foo: Foo=ARRAY(0x827ab44), foo field = is foo
(2) bar: Foo=ARRAY(0x827ab44), bar field = is bar
(3) foo: Foo=ARRAY(0x827ab44), foo field = is bar
No such pseudo-hash field "bar" at my.pl line 25.