There are practical uses for call-backs. One use is to provide some user of a Perl module a way to modify the behavior of that module. Here is a very simple example: 
use strict;

package Foo;
use Carp;

sub new {
   my ($class,$msg) = @_;
   my $self = {msg => $msg};
   return bless $self,$class;
}

sub print_me {
   my ($self,$cb) = @_;
   croak "not a code ref" unless ref $cb eq 'CODE';
   return $cb->($self->{'msg'});
}

package main;

my $foo = Foo->new('hello world');

print $foo->print_me(sub {ucfirst shift}), "\n";

[download]
Now the user can specify how they want the message printed. Like i said, a very simple example, but i am sure you can imagine this module doing a lot more behind the scenes. In these cases, providing a call-back instead of providing a list of choices can make a module more flexible, and keep you from maintaining that list of choices.

UPDATE - drats. Just when i though i knew what a closure was .... perrin pointed out that this is indeed, not a closure ... a good example for a anonymous subs maybe, but not a closure. I stand corrected and apologetic to the 13 people that voted this node up.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)

In reply to (jeffa) Practical Use For What jeffa Thought A Closure Was (3Re: Style Question on Closures) by jeffa
in thread Style Question on Closures by jynx

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