sub count
{
    my $self=shift;
    if (@_) { $self->{count} += shift }
    return $self->{count};
}

my $value = 5;
$self->counter +=  $value

sub count :lvalue{
     my $self=shift;
     if (@_) { $self->{count} += shift }
     $self->{count};
}

{
    package Class;
    use strict;
    use warnings;
    use Scalar::Util qw(weaken);
    my @objects;

    sub new {
        my ( $class ) = @_;

        # Objekt erstellen
        my $self = bless {}, $class;

        # zum array hinzufügen
        push @objects, $self;
        # Wert weaken
        weaken( $objects[-1] );

        # Object zurück geben
        return $self;
    }

    sub count {
        my ( $self ) = @_;
        return scalar @objects;
    }
}

printf "Anzahl: %d\n", Class::count;

my $new1 = Class->new;
my $new2 = Class->new;

printf "Anzahl: %d\n", $new1->count;

{
    my $new3 = Class->new;
    printf "Anzahl: %d\n", $new3->count;
}

printf "Anzahl: %d\n", $new1->count;