Using a log object in another object without passing it as a parameter

thezip has asked for the wisdom of the Perl Monks concerning the following question:

Consider the following toy script that uses a home-grown logging module Log, and the module Foo:

#!/usr/bin/perl

use strict;
use warnings;
use Log;
use Foo;

my $log = Log->new( { 'logfile' => 'log.txt', 'caller' => $0 } );
my $foo = Foo->new();

...
# do some stuff

$foo->printNum(5);
[download]

And the modules Log and Foo:

package Log;
use strict;
use warnings;

sub new {
  my ($class, $args) = @_;
  open (my $fh, ">>", $args->{'logfile'}) || die "Oops...\n";

  my $self = { 
    _LOGFILE => $args->{'logfile'},
    _CALLER  => $args->{'caller'},
    _FH          =>  $fh,
};
  return bless($self, ref($class) || $class);
}

sub writeError {
  my ($self, $msg) = @_;
  print $msg, "\n";
}

sub get_logger {
  ...
  # What should this code be to allow the Log->writeError()
  #  call (below in Foo) to succeed???
  ...
}

1;
[download]

package Foo;

use strict;
use warnings;
use Log;

my $log = Log->get_logger();

sub new {
  my $class = shift;
  my $self = {};
  return bless($self, ref($class) || $class);
}

sub printNum {
  my ($self, $num)  = @_;

  my $correct_num = 4;
  if ($num != $correct_num) {
    $log->writeError("I got a $num instead of a $correct_num!");
  }
}

1;
[download]

Is there a way to do this without passing $log as a parameter into Foo?

Your wish is my commandline.

Comment on Using a log object in another object without passing it as a parameter Select or Download Code

Replies are listed 'Best First'.
Re: Using a log object in another object without passing it as a parameter by pc88mxer (Vicar) on Aug 08, 2008 at 02:54 UTC
You need to use the Singleton pattern. Something like: `package Log; my $instance; ... sub get_logger { unless ($instance) { $instance = ...; # create the Log instance here # another option is to throw an exception } $instance; }` [download]	[reply] [d/l]