use strict;

my @foo;
push @foo, Foo->new() for (0..4);

package Foo;

{
   my $count = 0;
   sub get_count { return $count }
   sub inc_count { return ++$count }
}

sub new { 
   my $class = shift;

   $class->inc_count();
   print STDERR 'there are ', $class->get_count(), " instances\n";

   my $self  = {
      bar => 42
   };
   return bless $self, $class;
}
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print $Foo::count, "\n";
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jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

Damian's example is fine if you need to hide all variables behind methods, but the use of closures often confuses newbies. The simple answer to this question is to just use a (package-scoped) global:

use strict;

my @foo;
push @foo, Foo->new() for (0..4);

package Foo;
use vars qw($count);

sub new { 
   my $class = shift;

   $count++;
   print STDERR 'there are ', $count, " instances\n";

   my $self  = {
      bar => 42
   };
   return bless $self, $class;
}
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You may also want to look at the following CPAN modules that make management of class data easy:

Class::Data::Inheritable and Class::MethodMaker (see static_get_set method).

Another approach in newer perls gives something that looks very C-like in use. Make foo an lvalue accessor which takes no arguments:

BEGIN {
    my $foo = "default";
    sub foo () : lvalue { $foo }
}
print foo, $/;
foo = "special";
print foo,$/;
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The BEGIN block is only needed to get the "default" value in early (completely unneeded in this simple case). In a module, you can leave 'foo' off the @EXPORT_OK list so it's perlishly private to the module package.

For thread safety, you'd want the 'locked' attribute, besides 'lvalue'.

Update: Added clarification on the BEGIN block, and an unwise adverb.

After Compline,
Zaxo

package baz;
{
my $static=1;
sub new{return bless my $x;}
}
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