Chapter 2

To support this usage, BOA::Logger would need to be modified to initialize a 

$VERSION package variable:

package BOA::Logger;

$VERSION = 1.1;

Since these features are provided as method calls in a parent class, child 

classes can override them and provide their own implementations. This enables 

classes to lie to the rest of the world about their inheritance, capabilities, and even 

version. In Perl, things are not always as they appear.

Overloaded Modules

Object oriented programming can be cumbersome. Everything is a method call, 

and sooner or later all your method calls start to look the same. Overloading your 

modules provides a way to simplify code that uses your module. It allows you to 

express code like the following:

$foo >add(10);

print "My favorite cafe is " . $cafe >name() . "\n";

in a more natural way:

$foo += 10;

print "My favorite cafe is $cafe\n";

Overloading enables your objects to work with Perl's existing math and 

string operators. When a Perl operator is used with an object of an overloaded 

class, a method is called. You specify which operators you are overloading and 

which methods to call using the overload pragma.

16

package My::Adder;

use overload  +  => "add",

                 => \&subtract;

The overload pragma takes a list of key value pairs as an argument. The keys are 

symbols representing the various operators available for overloading. The values 

specify the method to call when the operator is used; this can be expressed as a 

16. A pragma is loosely defined as a module that functions as a compiler directive; it changes the 

way Perl compiles the code that follows. The pragmas that come with Perl all have lowercase 

names.

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