eval {
    no strict "refs";

    require "$fqn_file";

    local $SIG{'__DIE__'};
    $ref = exists ${ $foo . '::' }{ 'f_preferred' } 
         ? \&{$foo . "::f_preferred"} 
         : undef;
};
warn $@ if $@;

##</code><code>##

sub f_preferred;