Perl in a Nutshell, 2nd Edition

Attribute::Handlers

Implements a simpler definition of attribute handlers. When inherited by a package, Attribute::Handlers allows that package’s class to define handler subroutines for specific attributes. When inherited by a package, these handlers will be called by the same names as the original attribute-handling subroutines. Attribute handlers will be called at one of the following compilation phases: BEGIN, CHECK, INIT, or END blocks. Note that Attribute::Handlers is shipped with the Perl source kit as of Version 5.8.

Handlers are defined as subroutines and named as the desired attribute. In the following example, the attribute is :ATTR, which lives in a subroutine that’s called Nate1() in the HandlerBing class:

package HandlerBing;
use Attribute::Handlers;
sub Nate1 :ATTR {
    my(@attrs) = @_; # We simply want to test by dumping the attributes
    print "attributes: \n", 
       join("\n", @attrs), "\n";
}
 # true.
1;

This stub for the HandlerBing class creates a handler for the attribute :Nate1. When you want to use this handler while within HandlerBing, you can do the following:

sub Nate2 :Nate1 {
    my (@stuff) = @_;
        print STDERR "in Nate2 ", join("\n", @stuff), "\n";
}

When you call Nate2, it invokes the Nate1 handler and passes the following elements into the @_ array:

0

The name of the package in which the handler was declared

1

A reference to the symbol table entry (a typeglob) that contains the subroutine

2

A reference to the subroutine

3

The name of the attribute itself

4

Any data associated with ...