package Dog;

sub new {
    my $pkg = shift;
    bless {
        intelligence => shift,
    }, $pkg;
}

##</code><code>##

sub is_stupid {
    my $self = shift;
    return $self->{inteligence} < 3;
}

##</code><code>##

my $lassie = Dog->new(10);
print "Lassie is " $lassie->is_stupid ? "dumb" : "smart";

##</code><code>##

package Dog;
use fields qw/intelligence/;

sub new {
    my $pkg = shift;
    my $self = $pkg->fields::new();
    $self->{intelligence} = shift;
    $self;
}

##</code><code>##

my Dog $lassie; # perl knows, at compile time, that lassie isa Dog

##</code><code>##

package Dog;
use fields qw/intelligence/;

sub new {
    my $pkg = shift;
    my Dog $self = $pkg->fields::new;
    $self->{inteligence}; # typo again, but this time it doesn't compile
    $self;
}