Chapter 2

To provide the advertised enhanced functionality, the class will override the 

write() method. Overriding is when a child class replaces a parent class's method. 

Here's a new write() method that puts a timestamp on every log line. This code 

would be placed in BOA/Logger/Enhanced.pm:

sub write {

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

   $message = localtime(time) . " : " . $message;

   $self >{fh} >print($message) if $level <= $self >{level};

}

The method modifies the $message parameter to contain a timestamp and then 

prints out the line in the same way as the original BOA::Logger::write(). Here's an 

example using the new module:

use BOA::Logger::Enhanced;

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

$logger >level(10);

$logger >write(10, "The log level is at least 10!");

When BOA::Logger::Enhanced >new() is called, Perl first looks in the 

BOA::Logger::Enhanced package to see if a subroutine called new() is defined. 

When it finds that there is no BOA::Logger::Enhanced::new(), Perl checks to see if 

@ISA is defined and proceeds to check each package name listed in @ISA for the 

required method. When it finds BOA::Logger::new(), it calls the subroutine with 

two arguments, BOA::Logger::Enhanced and logs/boa.log. BOA::Logger::Enhanced 

gets assigned to $pkg in BOA::Logger::new() and used in the call to bless():

bless($self, $pkg);

The result is that BOA::Logger::new() returns an object in the BOA::Logger::Enhanced 

class without needing to know anything about BOA::Logger::Enhanced! Isn't Perl 

great?

CAUTION Don't be fooled by the similar class names no 

automatic inheritance is happening between BOA::Logger and 

BOA::Logger::Enhanced. Inheritance must be explicitly declared 

through @ISA to be used.

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