Perl Factory Method Pattern?

I am looking for a pattern for a Class Factory Method pattern in perl. I am developing a class that I expect to have at least three subclasses that can be instanciated. The base class will define the interface and each of the subclass will provide a different implementation for the platform where class is invoked. I have written several of these, but each time I wonder if there is a pattern out there that avoids some of the pitfalls or, worse yet, there are pitfalls have yet to encounter!

I know that there is a Package to do this via inheritance: Class::Factory However I do not have access to that Class in our standard Perl installation and I would like to minimize external dependencies.

package ProcInfo;

use Carp;
use strict;
use warnings;


our $VERSION = '0.01';

sub new 
{
  my $class = shift;
  my $self = {};
  bless $self, $class;
  $self->_init();
  return $self;
}

sub _init
{
  my $self = shift;
  my $osModule = "ProcInfo_$^O";

  # Load the subclass if it isn't already loaded.
  eval "require $osModule";
  if($@)
  {
    croak "Could not load OS ProcInfo Module:$osModule. [$@]";
  }
  
  # rebless self using subclass.
  bless $self, $osModule;
  $self->_init(@_);
  
  return $self;
}

sub method_1
{
  return 1;
}

1;
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Some question I have about the base class implementation:

If I know that I'm going to rebless the object to a subclass. Is there any advantage to blessing it in the first place in the new?
Is the rebless in the _init the right way to recast self to another class?

The skeleton for each sublcass would looking like this and it would be stored in ProcInfo_linux.pm:

package ProcInfo_linux;

use strict;
use warnings;
use base qw|ProcInfo|;

our $VERSION = '0.01';

sub _init
{
  my $self = shift;
  return $self;
}

sub method_1
{
  return 1;
}

1;
[download]

Finally, here is my test script (ProcInfo.t):

use Test::More tests => 3;
BEGIN { use_ok('ProcInfo') };


my $pInfo = new ProcInfo;
is(ref($pInfo), "ProcInfo_$^O", "Factory new Works");
ok($pInfo->method_1());
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Re: Perl Factory Method Pattern?
by dragonchild (Archbishop) on Oct 11, 2004 at 19:42 UTC

... and I would like to minimize external dependencies.

That is a feeling that many share, but I don't think it is worthwhile. CPAN exists so that the mainline distribution of Perl doesn't bloat to 10G, 90% any given user will not need. Most of the applications you can think of in Perl require at least 10-20% of their module code to be downloaded from CPAN. For example, one of the most downloaded module from CPAN is DBI. If CGI wasn't in the mainline, it would be the most downloaded module.

Download Class::Factory and just deal with it. CPAN isn't an external dependency - it's one of the primary reasons Perl is worth using.

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