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(jeffa) Practical Use For What jeffa Thought A Closure Was (3Re: Style Question on Closures)

by jeffa (Bishop)
on Jan 01, 2002 at 23:26 UTC ( #135537=note: print w/replies, xml ) Need Help??


in reply to Re: Re: Style Question on Closures
in thread Style Question on Closures

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";
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)
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