use UNIVERSAL::require;

my $fetcher_class = choose_fetcher_class();

my $fetcher = $fetcher_class->new;

# this is the good part
# this line of code does not care what driver it's using, as
# long as the subclass of MyApp::URLFetcher is implemented correctly
# isn't polymorphism great?
my $content = $fetcher->get($url);

sub choose_fetcher_class {
    foreach my $driver (qw/LWP NetFTP/){
        my $class = "MyApp::URLFetcher::$driver";
        # UNIVERSAL::require let's us avoid an eval
        return $class if $class->require;
    }
    die "couldn't load any driver";
}