Chapter 3

But most users of the module will take the path of least resistance and import 

everything:

use BOA::Network;  # imports everything in @BOA::Network::EXPORT

The practice of exporting everything by default is known as namespace pollution

and it has a justifiably bad name for a number of reasons. If a group of modules are 

all exporting symbols by default, there's a good chance some of the symbols will 

conflict. Even worse, upgrading a module that exports everything by default can 

suddenly cause client code to fail by exporting a new symbol that causes a conflict.

Exporting everything by default also makes deciphering code more difficult. 

For example, imagine you've been given the task of debugging this code:

use Some::Module;

use Some::Other::Module;

use Yet::Another::Module;

some_call( ... );

If you're trying to figure out why some_call() is failing, you'll first have to 

search through each used module to determine where some_call() is being 

imported from. Contrast that to this case:

use Some::Module qw(some_call some_other_call);

use Some::Other::Module qw(foo bar);

use Yet::Another::Module qw(BIF BAZ);

some_call( ... );

Now it's immediately obvious that some_call() is being imported from Some::Module.

Fortunately the Exporter comes equipped with an alternative to @EXPORT that 

can be used to enforce the preferred explicit importing. Just change @EXPORT to 

@EXPORT_OK and modules will have to declare their imports explicitly. For example, 

if BOA::Network is changed to use @EXPORT_OK as follows:

package BOA::Network;

require Exporter;

@ISA = qw(Exporter);

@EXPORT_OK = qw(open_socket

                send_message

                receive_message

                close_socket

                start_server

                stop_server);

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