# User doesn't mind if it is local or remote, he wants the data
package Lookup;
...
sub is_user_in_cache { ... }
sub get_user_data { warn 'You should implement this method!'; }
...
package Lookup::Remote;
use base 'Lookup';
sub get_user_data { ... }
...
package main;
use Lookup::Remote;
my $lookup = Lookup->new({ remote_uri => $uri, });

use User;
# Tell User class the lookup method it will use.
User->set_lookup($lookup);
my $user = User->new({ id => 1234, });