Chapter 3

a class can provide. In the last chapter I demonstrated how to provide accessor 

mutators by writing a method for each attribute. When the method has no param 

eters, it returns the value of the attribute; with one parameter, it sets the value of 

the attribute.

It doesn't take long before writing accessor mutator methods gets old. Every 

one is essentially the same. Fortunately, there are a number of better ways to 

choose from!

Auto Rolling Your Own

The basic problem is simple you have a number of subroutines to generate, and 

they all do the same thing on different data. Fortunately, Perl is a highly dynamic 

language, and it's easy to generate new subroutines at runtime. Here's an example 

that creates a simple accessor mutator for a set of attributes stored in the package 

variable @ATTRIBUTES:

package BOA::Logger;

# initialize array of attribute names

@ATTRIBUTES = qw(filename level format);

# create a subroutine for each attribute

foreach my $attribute (@ATTRIBUTES) {

   *$attribute = sub {

       my $self = shift;

       $self >{$attribute} = shift if @_;

       return $self >{$attribute};

    }

}

This block of code works by assigning a closure to a symbol table entry with the 

same name as the attribute. After this code runs, there will be three new methods 

available in the BOA::Logger package filename(), level(), and format(). If you 

needed to add a new attribute to the package, it would be a simple matter of 

adding it to @ATTRIBUTES.

Another way to accomplish the same effect is to use AUTOLOAD(). When you call 

a method on an object that doesn't exist in the object's class or any parent classes, 

Perl looks to see if the class has a method in it called AUTOLOAD(). If not, Perl will 

traverse the inheritance hierarchy the same way it does when looking for normal 

methods. When Perl finds a suitable AUTOLOAD() method, the package global 

$AUTOLOAD is set to the full name of the method being called, and AUTOLOAD() is called.

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