Module Design and Implementation

Now the subroutine can be called like this:

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

This style makes it obvious that both $status and $reply are values returned by the 

subroutine.

Consider allowing your routines to behave differently in list and scalar context 

using the wantarray() built in. It's much easier to use a subroutine that knows to 

return a count of its results in scalar context than to have to assign the results to an 

array and take its length. This also allows you to mimic the way many Perl built ins 

use context to determine their behavior (such as localtime and split). Here's a 

subroutine that returns all the values currently in a message queue in list context 

and the number of messages in scalar context:

sub get_messages {

   if (wantarray) {

     return @MESSAGES;             # return all the messages in list context

   } else {

     return $MESSAGE_COUNT;        # return the message count in scalar context

   }

}

Using the Exporter

Many functional modules will use the Exporter to make their subroutines available 

in the user's package. This is very convenient, but doing it in the simplistic way 

presented in the last chapter has some drawbacks. To refresh your memory, the 

simplest way to use the Exporter is to export everything by default:

package BOA::Network;

require Exporter;

@ISA = qw(Exporter);

@EXPORT = qw(open_socket

             send_message

             receive_message

             close_socket

             start_server

             stop_server);

With this setup it's possible to selectively import just the symbols you need:

use BOA::Network qw(open_socket send_message close_socket);

79

79