package MyApp::URLFetcher::LWP;
use base qw/MyApp::URLFetcher/;

use LWP::Simple;

# define the most convenient interface you can think of
# if you need just the contents of a URL in a string, do that
sub get_url_to_str {
    my $url = shift;
    get($url); # our chosen interface is simple with LWP
}

##</code><code>##

package MyApp::URLFetcher::NetFTP;
use base qw/MyApp::URLFetcher/;

use Net::FTP;

sub get_url_to_str {
    my $self = shift;
    my $url = shift;

    # I don't know Net::FTP
    # either way, our interface is a bit harder to pull off 
    # with Net::FTP
    # but this complexity will be in the software anyway
    # it's better to hide it here
    my $f = Net::FTP->new; # ...
    # ...
    $f->get("...");
}

##</code><code>##

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";
}