Chapter 3

Add a few more optional parameters, and pretty soon the average call is using 

more undefs than values!

Contrast this to the call with named parameters:

check_mail(imap_sever => $imap_server,

           username   => $username,

           password   => $password,

           retries    => 3);

Named parameter subroutines will automatically treat missing keys as undef so 

there's no need to put them in just for padding.

Return Values

If you need to return multiple values, return a list or a reference to an array. Avoid 

the tendency to slip into C mode and make your users pass in output parameters 

by reference. For example, the hobnob() subroutine sends a message to the BOA 

satellite and retrieves a response. It has two values to return a status flag indi 

cating success or failure and the received message. In C mode, it might look like 

the following:

sub hobnob {

   my ($message, $reply_ref) = @_;

   my $status = _send_message($message);

   $$reply_ref = _get_message();

   return $status;

}

It would be called like this:

$reply = "";

$status = hobnob("Hello out there!", \$reply);

The $reply variable is passed by reference and the retrieved message is filled in.

A simpler and more Perl ish way to do the same thing is to simply return a list 

of two values:

sub hobnob {

   my ($message) = @_;

   my $status = _send_message($message);

   my $reply = _get_message();

   return ($status, $reply);

}

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