list-of-instances.pl

use strict;
use warnings;
use Data::Dumper;

{
	package My::Example;
	use Moose;
	use Scalar::Util qw(weaken);
	use Hash::Util::FieldHash::Compat qw(fieldhash);
	
	has name => (is => 'ro');
	
	{
		fieldhash my %instances;
		sub BUILD {
			my $self = shift;
			weaken( $instances{$self} = $self );
		}
		sub instances {
			# might want to think about sorting them
			# in a non-random order
			values %instances;
		}
	}
}

my $alice = My::Example->new(name => 'Alice');
my $bob   = My::Example->new(name => 'Bob');
my $carol = My::Example->new(name => 'Carol');

print Dumper [ My::Example->instances ];

undef $bob;

print Dumper [ My::Example->instances ];