Chapter 2

Here's an example of using the module, which would be placed in a separate 

script file:

use BOA::Logger;

my $logger = BOA::Logger >new( logs/boa.log );

$logger >level(10);

$logger >write(10, "Hello world!");

One thing to notice is that making the module object oriented allows you to sim 

plify the names of the subroutines in BOA::Logger. This is because object oriented 

modules should never export their methods. Thus there's no need to worry about 

confusion with other subroutines called level() and write(). Another advantage 

of the object oriented BOA::Logger is that you can have multiple loggers active at 

the same time with different log files and different log levels.

Accessors and Mutators

The level() method shown earlier is called a mutator it is used to change, or 

mutate, the value of the level attribute. It is not an accessor since it doesn't allow 

the user to query the current value of the level attribute. An accessor for the value 

of level could potentially be useful a user of the module could avoid executing 

costly debugging code if the log level is set too low to show the results. Here's a new 

level() method that functions as both an accessor and a mutator:

sub level {

   my ($self, $level) = @_;

   $self >{level} = $level if @_ == 2;

   return $self >{level};

}

Now it's possible to call the level() method with no arguments to receive the current 

value of the level attribute. For example, this checks the log level before calling write():

if ($logger >level() >= 5) {

   $logger >write(5, "Here s the full state of the system: " . dump_state());

}

This way you can avoid calling dump_state() if the result will never be printed.

Writing accessor mutators for each attribute in your object enables you to 

perform checks on the value being set. For example, it might be useful to verify 

that the level value is a nonnegative integer. One way to do this is to check it with a 

regular expression that only matches digits:

42