In Perl, how do I put multiple packages in a single .pm file?

Question

I'm pretty sure that I read somewhere that it's possible, but there are a few gotchas that you need to be aware of. Unfortunately, I can't find the tutorial or page that described what you need to do. I looked through the Perl tutorials, and didn't find the one that I remember reading. Could someone point me to a page or document that describes how to put multiple packages into a single .pm file?

Answer 1

You simply start off the new package with another package statement:

package PackageOne;

# ...... code

package PackageTwo;

# .... more code

Problems with this approach

Answer 2

How to do it: just issue multiple package instructions.

Gotchas I can think of: my-variables aren't package-localized, so they're shared anyway. Before you issue any, you're in package main by default.

Answer 3

In general, it is better to stick with the one package per file rule. What are you trying to achieve?

#!/usr/bin/perl

package My::A;
use strict; use warnings;

sub new { my $class = shift; bless \$class => $class }

package My::B;

use base 'My::A';
use strict; use warnings;

sub whoami { ${$_[0]} }

package My::C;

use base 'My::B';
use strict; use warnings;

package main;
use strict; use warnings;

my $x = My::B->new;
my $y = My::C->new;

print $_->whoami,"\n" for $x, $y;

Answer 4

This is how I normally do it:

use strict;
use warnings;
use 5.010;

{
    package A;
    sub new   { my $class = shift; bless \$class => $class }
    sub hello { say 'hello from A' }
}

{
    package B;
    use Data::Dumper;
    sub new   { my $class = shift; bless { @_ } => $class }
    sub hello { say 'Hello from B + ' . shift->dump       }
    sub dump  { Dumper $_[0] }
}

$_->hello for A->new, B->new( foo => 'bar' );

/I3az/