Hi v_melnik,

Globals have a bad reputation because they are so commonly misused. But that doesn't make all globally accessible values bad: Will you ever have a need for more than one logger object in your entire application? And you can still use an OO approach and encapsulate the retrieval of the globally accessible value in a method, allowing for you to later change how loggers are retrieved (admittedly, if you make it a class method, that limits it a bit, but luckily in Perl class and instance methods are very similar). Here are just a few examples of the many possibilities:

use warnings;
use strict;
use feature 'state';

package Library;
sub new { bless {}, shift }
sub logger { # Just an example;
    # could be class or instance method / property,
    # could hand out different logger objects.
    state $logger = Library::Logger->new;
    return $logger;
}

package Library::Logger;
sub new { bless {}, shift }
sub log { shift; print "[".gmtime." UTC] @_\n" }

package Library::Foo;
sub new { bless {}, shift }
sub foo { Library->logger->log("access via class method works") }

package Library::Bar;
use parent -norequire, 'Library';
sub bar { shift->logger->log("inheritance works") }

package Library::Quz;
sub new { my $class = shift; bless {@_}, $class }
sub library { shift->{library} }
sub quz { shift->library->logger->log("access via property works") }

package main;
Library::Foo->new->foo;
Library::Bar->new->bar;
my $lib = Library->new;
$lib->logger->log("access via instance method works");
Library::Quz->new(library=>$lib)->quz;

[download]

Update: Added Library::Quz class and updated example code accordingly; added some comments.

Hope this helps,
-- Hauke D

In reply to Re: Passing the logger's object (updated) by haukex
in thread Passing the logger's object by v_melnik

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